testagent-transform: Phase-1 trust-chain demo agent (DEV-610)

Minimal CLI agent process that end-to-end demonstrates the Transform step
of the ProofedMesh trust chain:

  1. Fetches an approval attestation from the transparency-log by
     attestation_ref (`sha256:<hex>`).
  2. DSSE-verifies the fetched envelope against a pinned approval-signer
     ed25519 keyring; stops before any signing call on failure.
  3. Builds an in-toto v1 Statement with predicateType
     `basicstack.de/attestations/transform/v1`, operation
     `expense.map_to_sink`, materials[0].attestation_ref = approval_ref,
     and subject[0].digest.sha256 = sha256(canonical(handover_payload)).
  4. Calls signing-service /api/v1/sign/dsse with BOTH identities:
     Authorization: Bearer <pocket-id client_credentials token> AND
     X-Workload-Token: <projected SA token from
     /var/run/secrets/tokens/trust-api>.
  5. Submits the returned DSSE envelope + content_hash to the
     transparency-log /api/v1/log/entries.
  6. POSTs the canonical handover_payload bytes to the dummy-sink
     (schema sink.dummy.v1), carrying the transform content_hash on the
     X-Attestation-Ref header.

Tests use httptest for all four backends:

  - Happy path (verifies the bytes sent to the sink match the signed
    subject digest and that the TLog recorded the same content_hash the
    agent returned).
  - Invalid approval signature -> stops before sign-call; TLog and sink
    untouched.
  - Signing-service returns 403 signing_denied -> surfaced as
    signer.ErrSigningDenied; TLog and sink untouched.
  - Missing Pocket-ID token -> fails before any network call.

Includes PocketID client_credentials TokenSource (OIDC discovery + cache)
and ProjectedSATokenSource (reads kubelet-managed Volume) mirroring
admin-api/approval-service.

Non-scope: no read-side attestations (Phase 2), no K8s/CI image build
wiring (follow-up ticket).

Co-Authored-By: Paperclip <noreply@paperclip.ing>

db/trust/migrations/0004_approval_sessions.down.sql

@@ -0,0 +1,11 @@
+-- Rollback for 0004_approval_sessions.
+-- DESTRUKTIV: entfernt sämtliche Approval-Historie (Sessions, Previews,
+-- bestätigte Approvals). Die in Trillian abgelegten DSSE-Envelopes bleiben
+-- erhalten, aber die Vorlagen und Session-Hintergründe sind weg; Audits,
+-- die auf H_content vs. gespeicherte canonical content zurückgreifen,
+-- verlieren damit ihren lokalen Referenzpunkt. Vor Anwendung IMMER einen
+-- Dump der trust-DB ziehen.
+
+DROP TABLE IF EXISTS approvals;
+DROP TABLE IF EXISTS approval_previews;
+DROP TABLE IF EXISTS approval_sessions;

db/trust/migrations/0004_approval_sessions.up.sql

@@ -0,0 +1,102 @@
+-- Migration: 0004_approval_sessions
+-- Content-gebundene Approvals gemäß docs/architecture/v1.1.md §4.3 und
+-- Phase-1-Spezifikation [DEV-608](/DEV/issues/DEV-608).
+--
+-- Drei Tabellen, strikt in der Reihenfolge der Session → Preview → Confirm
+-- Pipeline des approval-service:
+--
+--   1. `approval_sessions` — eine durch die Pocket-ID-Session gestützte
+--      Approval-Session; sie bindet (session_id, user_sub) an ein Ablauf-
+--      datum und wird vom Approval-UI pro Browser-Login einmal erzeugt.
+--   2. `approval_previews` — ein serverseitig gerendertes Freigabe-Objekt;
+--      Content-Hash (`H_content`), Salt und Challenge-Nonce werden gleich
+--      bei der Vorschau festgenagelt, damit das Confirm-Step eine *andere*
+--      Payload nicht nachträglich unterschieben kann.
+--   3. `approvals` — die bestätigte, DSSE-signierte Approval. `tlog_status`
+--      spiegelt den TLog-Einwurf; `attestation-pending` bedeutet die Row
+--      ist persistiert, der TLog-Submit aber noch nicht quittiert und wird
+--      vom attest-reconciler bzw. einem späteren Worker nachgezogen.
+--
+-- Design-Entscheidungen:
+--   * Alle `*_id`-Spalten sind TEXT (opaque IDs; Service-generiert, nicht
+--     UUID gezwungen) — bleibt kompatibel mit dem bestehenden Stil der
+--     Trust-DB.
+--   * `content_canonical` wird in Preview mitgespeichert, damit Confirm
+--     den Hash deterministisch nachrechnen und das signierte Statement
+--     ohne erneutes Rendern aufbauen kann.
+--   * `tlog_status` ist ein Enum via CHECK statt pg-native ENUM, um die
+--     Migration ohne CREATE TYPE drop-safe zu halten.
+
+CREATE TABLE IF NOT EXISTS approval_sessions (
+    session_id    TEXT PRIMARY KEY
+                     CHECK (length(session_id) BETWEEN 16 AND 128),
+    user_sub      TEXT NOT NULL
+                     CHECK (length(user_sub) BETWEEN 1 AND 256),
+    active_until  TIMESTAMPTZ NOT NULL,
+    created_at    TIMESTAMPTZ NOT NULL DEFAULT NOW()
+);
+
+CREATE INDEX idx_approval_sessions_user
+    ON approval_sessions (user_sub);
+
+CREATE INDEX idx_approval_sessions_active_until
+    ON approval_sessions (active_until);
+
+CREATE TABLE IF NOT EXISTS approval_previews (
+    preview_id          TEXT PRIMARY KEY
+                           CHECK (length(preview_id) BETWEEN 16 AND 128),
+    session_id          TEXT NOT NULL
+                           REFERENCES approval_sessions(session_id)
+                           ON DELETE CASCADE,
+    content_hash        TEXT NOT NULL
+                           CHECK (content_hash ~ '^sha256:[0-9a-f]{64}$'),
+    content_canonical   BYTEA NOT NULL,
+    salt                BYTEA NOT NULL
+                           CHECK (length(salt) BETWEEN 16 AND 64),
+    challenge_nonce     BYTEA NOT NULL
+                           CHECK (length(challenge_nonce) BETWEEN 16 AND 64),
+    verification_digits TEXT NOT NULL
+                           CHECK (verification_digits ~ '^[0-9]{4,12}$'),
+    expires_at          TIMESTAMPTZ NOT NULL,
+    created_at          TIMESTAMPTZ NOT NULL DEFAULT NOW(),
+    consumed_at         TIMESTAMPTZ
+);
+
+CREATE INDEX idx_approval_previews_session
+    ON approval_previews (session_id);
+
+CREATE INDEX idx_approval_previews_expires
+    ON approval_previews (expires_at)
+    WHERE consumed_at IS NULL;
+
+CREATE TABLE IF NOT EXISTS approvals (
+    approval_id      TEXT PRIMARY KEY
+                        CHECK (length(approval_id) BETWEEN 16 AND 128),
+    preview_id       TEXT NOT NULL
+                        REFERENCES approval_previews(preview_id),
+    session_id       TEXT NOT NULL
+                        REFERENCES approval_sessions(session_id),
+    user_sub         TEXT NOT NULL,
+    content_hash     TEXT NOT NULL
+                        CHECK (content_hash ~ '^sha256:[0-9a-f]{64}$'),
+    envelope_json    JSONB NOT NULL,
+    attestation_ref  TEXT NOT NULL
+                        CHECK (attestation_ref ~ '^sha256:[0-9a-f]{64}$'),
+    tlog_status      TEXT NOT NULL DEFAULT 'attestation-pending'
+                        CHECK (tlog_status IN ('attestation-pending',
+                                               'logged',
+                                               'failed')),
+    log_index        BIGINT,
+    tlog_error       TEXT,
+    confirmed_at     TIMESTAMPTZ NOT NULL DEFAULT NOW(),
+    logged_at        TIMESTAMPTZ,
+    CONSTRAINT approvals_log_consistency
+        CHECK ((tlog_status = 'logged') = (log_index IS NOT NULL))
+);
+
+CREATE INDEX idx_approvals_tlog_pending
+    ON approvals (confirmed_at)
+    WHERE tlog_status = 'attestation-pending';
+
+CREATE INDEX idx_approvals_user
+    ON approvals (user_sub, confirmed_at);

deploy/signing-service/00-serviceaccount.yaml

@@ -7,4 +7,7 @@ metadata:
     app.kubernetes.io/name: signing-service
     app.kubernetes.io/part-of: proofedmesh
     app.kubernetes.io/component: trust-core
-automountServiceAccountToken: true
+# The signing-service pod uses an EXPLICIT projected SA token
+# (deploy/signing-service/20-deployment.yaml) rather than the default
+# auto-mount, so this SA opts out of auto-mounting.
+automountServiceAccountToken: false

deploy/signing-service/01-rbac.yaml

@@ -0,0 +1,40 @@
+# RBAC for the signing-service's K8s TokenReview path (DEV-609).
+#
+# The signing-service verifies the caller's workload identity by handing the
+# `X-Workload-Token` header to the Kubernetes API server as a TokenReview.
+# That requires create on `tokenreviews.authentication.k8s.io`, which is
+# NOT part of any default role, so we grant it via a dedicated ClusterRole.
+#
+# The ClusterRole is intentionally narrow: `tokenreviews` + `subjectaccessreviews`
+# so the service can also diagnose "the token authenticated as X, is X allowed
+# Y?" patterns in Phase 2 without a second RBAC update.
+---
+apiVersion: rbac.authorization.k8s.io/v1
+kind: ClusterRole
+metadata:
+  name: signing-service-tokenreview
+  labels:
+    app.kubernetes.io/name: signing-service
+    app.kubernetes.io/part-of: proofedmesh
+    app.kubernetes.io/component: trust-core
+rules:
+  - apiGroups: ["authentication.k8s.io"]
+    resources: ["tokenreviews"]
+    verbs: ["create"]
+---
+apiVersion: rbac.authorization.k8s.io/v1
+kind: ClusterRoleBinding
+metadata:
+  name: signing-service-tokenreview
+  labels:
+    app.kubernetes.io/name: signing-service
+    app.kubernetes.io/part-of: proofedmesh
+    app.kubernetes.io/component: trust-core
+roleRef:
+  apiGroup: rbac.authorization.k8s.io
+  kind: ClusterRole
+  name: signing-service-tokenreview
+subjects:
+  - kind: ServiceAccount
+    name: signing-service
+    namespace: agent-trust

deploy/signing-service/20-deployment.yaml

@@ -26,7 +26,12 @@ spec:
         app.kubernetes.io/component: trust-core
     spec:
       serviceAccountName: signing-service
-      automountServiceAccountToken: true
+      # The signing-service MUST NOT get the default auto-mounted token
+      # because we need a projected token with an explicit `trust-api`
+      # audience so the pod SA token can be used to call the API server
+      # for TokenReview (the audience on the pod's own SA token is what
+      # the K8s API server will accept as Bearer credential).
+      automountServiceAccountToken: false
       securityContext:
         runAsNonRoot: true
         runAsUser: 65532
@@ -41,22 +46,42 @@ spec:
           args:
             - "-listen=:8081"
             - "-backend=memory"
-            - "-keys=trust-api/rate-change-signer-2026-q4"
+            - "-keys=trust-api/approval-signer-2026-q4,trust-api/agent-testagent-transform-2026-q4"
             - "-keys-from-env"
-            - "-bearers=$(SIGNING_BEARERS)"
+            - "-pocket-id-issuer=$(POCKET_ID_ISSUER)"
+            - "-pocket-id-audience=$(POCKET_ID_AUDIENCE)"
+            - "-k8s-tokenreview=on"
+            - "-registry-dsn=$(TRUST_PG_DSN)"
+            - "-policy-bundle=/etc/signing-service/policies/signing_service.rego"
           env:
-            # Pulled from the dev Secret below; see deploy/signing-service/README.md
-            # for the full secret shape and the SealedSecret recipe.
-            - name: SIGNING_BEARERS
+            # ---- Pocket-ID OIDC discovery (DEV-609) ----
+            - name: POCKET_ID_ISSUER
               valueFrom:
                 secretKeyRef:
-                  name: signing-service-dev
-                  key: SIGNING_BEARERS
-            - name: KEY_TRUST_API_RATE_CHANGE_SIGNER_2026_Q4
+                  name: signing-service-prod
+                  key: POCKET_ID_ISSUER
+            - name: POCKET_ID_AUDIENCE
               valueFrom:
                 secretKeyRef:
-                  name: signing-service-dev
-                  key: KEY_TRUST_API_RATE_CHANGE_SIGNER_2026_Q4
+                  name: signing-service-prod
+                  key: POCKET_ID_AUDIENCE
+            # ---- trust-api agent registry DSN (DEV-609) ----
+            - name: TRUST_PG_DSN
+              valueFrom:
+                secretKeyRef:
+                  name: signing-service-prod
+                  key: TRUST_PG_DSN
+            # ---- Signing keys (same shape as dev; swapped to prod Secret) ----
+            - name: KEY_TRUST_API_APPROVAL_SIGNER_2026_Q4
+              valueFrom:
+                secretKeyRef:
+                  name: signing-service-prod
+                  key: KEY_TRUST_API_APPROVAL_SIGNER_2026_Q4
+            - name: KEY_TRUST_API_AGENT_TESTAGENT_TRANSFORM_2026_Q4
+              valueFrom:
+                secretKeyRef:
+                  name: signing-service-prod
+                  key: KEY_TRUST_API_AGENT_TESTAGENT_TRANSFORM_2026_Q4
           ports:
             - name: http
               containerPort: 8081
@@ -77,17 +102,58 @@ spec:
             failureThreshold: 3
           resources:
             requests:
-              cpu: "50m"
-              memory: "64Mi"
+              cpu: "100m"
+              memory: "128Mi"
             limits:
-              cpu: "500m"
-              memory: "256Mi"
+              cpu: "1000m"
+              memory: "512Mi"
           securityContext:
             allowPrivilegeEscalation: false
             readOnlyRootFilesystem: true
             capabilities:
               drop:
                 - ALL
+          volumeMounts:
+            - name: kube-api-token
+              mountPath: /var/run/secrets/kubernetes.io/serviceaccount
+              readOnly: true
+            - name: opa-policy
+              mountPath: /etc/signing-service/policies
+              readOnly: true
+      volumes:
+        # Projected SA token the signing-service presents to the
+        # Kubernetes API server to authorize TokenReview calls. The
+        # projected volume also carries the API server CA, which the
+        # in-cluster TokenReviewer loads from
+        # /var/run/secrets/kubernetes.io/serviceaccount/ca.crt.
+        - name: kube-api-token
+          projected:
+            sources:
+              - serviceAccountToken:
+                  path: token
+                  # The API server audience — pod-SA tokens addressed to
+                  # the api server are what RBAC checks against.
+                  audience: "https://kubernetes.default.svc"
+                  expirationSeconds: 3600
+              - configMap:
+                  name: kube-root-ca.crt
+                  items:
+                    - key: ca.crt
+                      path: ca.crt
+              - downwardAPI:
+                  items:
+                    - path: namespace
+                      fieldRef:
+                        fieldPath: metadata.namespace
+        # OPA Rego policy source, mounted read-only. The ConfigMap is
+        # created from policies/sinks/signing_service.rego by GitOps
+        # (see deploy/signing-service/README.md).
+        - name: opa-policy
+          configMap:
+            name: signing-service-policy
+            items:
+              - key: signing_service.rego
+                path: signing_service.rego
       topologySpreadConstraints:
         - maxSkew: 1
           topologyKey: kubernetes.io/hostname

deploy/signing-service/README.md

@@ -9,7 +9,8 @@ directory assumes that file (or an equivalent) is already applied.
 
 ```
 deploy/signing-service/
-├── 00-serviceaccount.yaml       — ServiceAccount with projected SA token
+├── 00-serviceaccount.yaml       — ServiceAccount (opts out of auto-mount; a projected volume is used)
+├── 01-rbac.yaml                 — ClusterRole + Binding for TokenReview (DEV-609)
 ├── 10-secret-dev.example.yaml   — TEMPLATE for the dev-mode Secret
 ├── 20-deployment.yaml           — Deployment (non-root, read-only rootfs, distroless)
 ├── 30-service.yaml              — ClusterIP Service on :8081
@@ -17,6 +18,27 @@ deploy/signing-service/
 └── README.md                    — this file
 ```
 
+## Prod wiring (DEV-609)
+
+The Deployment reads the following prod flags via env:
+
+| Flag                   | Env                      | Purpose                                                                                   |
+| ---------------------- | ------------------------ | ----------------------------------------------------------------------------------------- |
+| `-pocket-id-issuer`    | `POCKET_ID_ISSUER`       | Pocket-ID OIDC issuer URL — enables JWKS validator (replaces static bearer table).         |
+| `-pocket-id-audience`  | `POCKET_ID_AUDIENCE`     | Expected `aud` claim on Pocket-ID tokens.                                                 |
+| `-k8s-tokenreview=on`  | (flag)                   | Enables K8s TokenReview on `X-Workload-Token` using the pod's projected SA token.         |
+| `-registry-dsn`        | `TRUST_PG_DSN`           | Postgres DSN for the trust-api `agents` table (DEV-607).                                  |
+| `-policy-bundle`       | (flag, file path)        | Rego file mounted at `/etc/signing-service/policies/signing_service.rego`.                |
+
+The OPA policy source lives at `policies/sinks/signing_service.rego`. Create
+the ConfigMap it is mounted from before applying the Deployment:
+
+```bash
+kubectl -n agent-trust create configmap signing-service-policy \
+  --from-file=signing_service.rego=policies/sinks/signing_service.rego \
+  --dry-run=client -o yaml | kubectl apply -f -
+```
+
 ## Apply order
 
 ```bash

policies/sinks/signing_service.rego

@@ -0,0 +1,74 @@
+# METADATA
+# title: Signing-service policy (ProofedMesh Phase 1)
+# description: |
+#   Decides whether an authenticated client may obtain a DSSE signature for a
+#   given key_ref. Enforces two independent conditions:
+#
+#     1. The Pocket-ID client identity (`sub` claim) and the Kubernetes
+#        ServiceAccount identity (`<ns>/<sa>` from TokenReview) resolve to the
+#        same agent row in the trust-api `agents` table.
+#     2. The requested `key_ref` is in the set of key_refs this agent's role
+#        is permitted to sign with.
+#
+#   Both lookups are passed in as `input.registry.by_pocket_id` and
+#   `input.registry.by_k8s`. The signing-service MUST perform both lookups
+#   from the DB and hand the raw rows (or `null` on no match) to OPA — the
+#   policy does not reach out to the DB on its own.
+# authors:
+#   - CTO Agent <cto@basicstack.de>
+# related_resources:
+#   - ref: docs/architecture/v1.1.md#user-content-44-identitaet-und-schluessel
+#   - ref: db/trust/migrations/0002_agents.up.sql
+package proofedmesh.sinks.signing_service
+
+import rego.v1
+
+default allow := false
+
+# Map agent_id → set of allowed key_ref prefixes. Prefixes end at the
+# quarter boundary so we can rotate the suffix (`-2026-q4`, `-2027-q1`, …)
+# without changing the policy. Keep this list in sync with the trust-api
+# agent registry seeds (db/trust/seeds/0001_phase1_agents.sql).
+agent_key_prefixes := {
+	"agent-approval-service": {"trust-api/approval-signer-"},
+	"agent-testagent-transform": {"trust-api/agent-testagent-transform-"},
+	"agent-dummy-sink": {"trust-api/dummy-sink-signer-"},
+}
+
+# Both registry lookups must have returned the SAME agent row and that row
+# must be internally consistent with the identities actually presented by
+# the caller (Pocket-ID `sub` and the K8s ServiceAccount reported by
+# TokenReview). Any null, mismatch, or absent field denies.
+identities_agree if {
+	input.registry.by_pocket_id.agent_id == input.registry.by_k8s.agent_id
+	input.registry.by_pocket_id.pocket_id_client == input.pocket_id_client
+	input.registry.by_pocket_id.k8s_namespace == input.k8s.namespace
+	input.registry.by_pocket_id.k8s_service_account == input.k8s.service_account
+	input.registry.by_k8s.pocket_id_client == input.pocket_id_client
+	input.registry.by_k8s.k8s_namespace == input.k8s.namespace
+	input.registry.by_k8s.k8s_service_account == input.k8s.service_account
+}
+
+key_ref_matches_role if {
+	some prefix in agent_key_prefixes[input.registry.by_pocket_id.agent_id]
+	startswith(input.key_ref, prefix)
+}
+
+allow if {
+	identities_agree
+	key_ref_matches_role
+}
+
+deny_reason contains msg if {
+	not identities_agree
+	msg := "pocket-id and k8s identities do not resolve to the same registry agent"
+}
+
+deny_reason contains msg if {
+	identities_agree
+	not key_ref_matches_role
+	msg := sprintf(
+		"agent %q is not permitted to sign with key_ref %q",
+		[input.registry.by_pocket_id.agent_id, input.key_ref],
+	)
+}

services/approval-service/README.md

@@ -0,0 +1,144 @@
+# approval-service
+
+Phase 1 der ProofedMesh content-gebundenen Approvals ([DEV-608](/DEV/issues/DEV-608),
+siehe `docs/architecture/v1.1.md §4.3`). Der Dienst nimmt menschliche
+Freigaben an, bindet sie kryptographisch an einen deterministisch gerenderten
+JSON-Inhalt (`H_content = sha256(canonical_json)`), verifiziert eine WebAuthn-
+Assertion gegen die Challenge `nonce || H_content` und erzeugt daraus eine
+DSSE-signierte Approval-Attestation, die ins Transparency-Log eingetragen
+wird.
+
+## Endpoints
+
+Alle Routen sind JSON-API, Pocket-ID-Session-Cookie-geschützt.
+
+| Methode | Pfad                        | Zweck                                                                                              |
+| ------- | --------------------------- | -------------------------------------------------------------------------------------------------- |
+| `POST`  | `/api/v1/sessions`          | Startet eine Approval-Session. Antwort: `{session_id, active_until}`.                              |
+| `POST`  | `/api/v1/approvals/preview` | Rendert Freigabe-Inhalt serverseitig, berechnet `H_content`, legt Challenge und Prüfziffer ab.    |
+| `POST`  | `/api/v1/approvals/confirm` | Nimmt die WebAuthn-Assertion entgegen, signiert und loggt die Approval.                            |
+| `GET`   | `/healthz`                  | Liveness.                                                                                          |
+
+### `POST /api/v1/sessions`
+
+Erzeugt eine Approval-Session an die aktuelle Pocket-ID-`sub`. `active_until`
+ist in Phase 1 fest auf `SessionTTL` (Default 15 min).
+
+### `POST /api/v1/approvals/preview`
+
+Request:
+
+```json
+{
+  "session_id": "sess_…",
+  "content": { "...application-defined..." }
+}
+```
+
+Response:
+
+```json
+{
+  "preview_id": "pv_…",
+  "content_hash": "sha256:<hex>",
+  "verification_digits": "734219",
+  "webauthn_challenge": "<b64url>",
+  "expires_at": "2026-01-01T12:00:00Z"
+}
+```
+
+`verification_digits` ist eine 6-stellige Prüfziffer aus `H_content`, die der
+Mensch im UI vor der Freigabe mit der Signaturaufforderung abgleichen MUSS.
+`webauthn_challenge` ist bereits `nonce || H_content` (b64url), damit der
+Browser direkt eine WebAuthn-Assertion anfordern kann.
+
+### `POST /api/v1/approvals/confirm`
+
+Request:
+
+```json
+{
+  "preview_id": "pv_…",
+  "assertion": {
+    "credential_id": "<b64url>",
+    "client_data_json": "<b64url>",
+    "authenticator_data": "<b64url>",
+    "signature": "<b64url>"
+  }
+}
+```
+
+Response:
+
+```json
+{
+  "approval_id": "ap_…",
+  "attestation_ref": "sha256:<hex>",
+  "log_index": 42,
+  "tlog_status": "logged"
+}
+```
+
+Wenn der TLog-Submit scheitert, bleibt die Row `tlog_status =
+"attestation-pending"`; die Antwort meldet dann `log_index: null,
+tlog_status: "attestation-pending"`. Ein späterer Reconciler zieht den
+Submit nach (ADR-0005, idempotent per `content_hash`).
+
+## Fehler
+
+| Zustand                                      | Code | Body `error.code`         |
+| -------------------------------------------- | ---- | ------------------------- |
+| Session abgelaufen / unbekannt               | 403  | `session_expired`         |
+| `H_content`-Mismatch (Assertion vs. Preview) | 400  | `content_hash_mismatch`   |
+| Challenge abgelaufen                         | 403  | `challenge_expired`       |
+| WebAuthn-Assertion ungültig                  | 401  | `assertion_invalid`       |
+| Signing-Service nicht erreichbar             | 502  | `signer_unavailable`      |
+
+## Phase 1 Scope
+
+- Store ist in-memory (`internal/store/memory.go`); Postgres-Impl ist in
+  `internal/store/postgres.go` als Skelett angelegt (Pattern aus
+  `admin-api/internal/store/postgres.go`). Die SQL-Migration liegt bereits
+  in `db/trust/migrations/0004_approval_sessions.*.sql`.
+- WebAuthn-Verifikation ist eine stdlib-only Shim im Stil von
+  `admin-api/internal/auth/pocket_id.go`: In-Memory-`Credential`-Store,
+  Ed25519-Assertion über `authenticator_data || sha256(client_data_json)`,
+  Challenge-Vergleich konstantzeitig. Die Datenformate sind
+  WebAuthn-kompatibel (b64url-encoded `client_data_json` mit `challenge`,
+  `type`, `origin`), damit das Phase-2-Umstieg auf
+  `github.com/go-webauthn/webauthn` ohne API-Bruch möglich bleibt.
+- Keine HTML/UI; nur JSON. Browser-Integration landet in einem Folge-Task.
+
+## Konfiguration
+
+Alle über Flags oder Env (`APPROVAL_*`):
+
+| Env / Flag                      | Default                     | Zweck                                                     |
+| ------------------------------- | --------------------------- | --------------------------------------------------------- |
+| `APPROVAL_LISTEN`               | `:8080`                     | HTTP-Listen-Adresse.                                      |
+| `APPROVAL_SIGNING_URL`          | *(required)*                | Base URL des signing-service (`/api/v1/sign/dsse`).       |
+| `APPROVAL_SIGNING_KEY_REF`      | `trust-api/approval-signer-2026-q4` | DSSE-Signaturschlüssel.                           |
+| `APPROVAL_SIGNING_TOKEN`        | *(optional)*                | Bearer-Token für signing-service (Phase 1 Static).        |
+| `APPROVAL_TLOG_URL`             | *(required)*                | Base URL des transparency-log.                            |
+| `APPROVAL_SESSION_TTL`          | `15m`                       | Lebensdauer einer Approval-Session.                        |
+| `APPROVAL_CHALLENGE_TTL`        | `2m`                        | Max. Zeit zwischen Preview und Confirm.                   |
+| `APPROVAL_WEBAUTHN_RP_ID`       | `trust.basicstack.de`       | WebAuthn relying party ID.                                 |
+| `APPROVAL_WEBAUTHN_RP_ORIGIN`   | `https://trust.basicstack.de` | Erlaubter Origin in `client_data_json`.                 |
+| `APPROVAL_POCKET_ID_ISSUER`     | *(required in prod)*        | Pocket-ID OIDC-Issuer.                                     |
+| `APPROVAL_POCKET_ID_CLIENT`     | *(required in prod)*        | Client-ID des approval-service.                           |
+
+## Tests
+
+```
+cd services/approval-service
+go test ./...
+```
+
+Deckt ab:
+
+- Happy Path (Session → Preview → Confirm → DSSE verifiziert und ins TLog
+  eingetragen).
+- Tampered `H_content` in der Assertion → 400.
+- Abgelaufene Challenge → 403.
+- Signing-Service antwortet nicht (connection refused) → 502.
+- TLog-Submit scheitert → Approval bleibt `attestation-pending`.

services/approval-service/cmd/approval-service/main.go

@@ -0,0 +1,149 @@
+// Command approval-service is the Phase-1 ProofedMesh content-binding
+// approval HTTP server. See services/approval-service/README.md for the
+// endpoint contract and configuration.
+package main
+
+import (
+	"errors"
+	"flag"
+	"log/slog"
+	"net/http"
+	"os"
+	"strings"
+	"time"
+
+	"basicstack.de/proofedmesh/services/approval-service/internal/auth"
+	"basicstack.de/proofedmesh/services/approval-service/internal/httpapi"
+	"basicstack.de/proofedmesh/services/approval-service/internal/service"
+	"basicstack.de/proofedmesh/services/approval-service/internal/sessions"
+	"basicstack.de/proofedmesh/services/approval-service/internal/signer"
+	"basicstack.de/proofedmesh/services/approval-service/internal/store"
+	"basicstack.de/proofedmesh/services/approval-service/internal/tlog"
+	"basicstack.de/proofedmesh/services/approval-service/internal/webauthn"
+)
+
+func main() {
+	cfg := struct {
+		Listen           string
+		SigningURL       string
+		SigningKeyRef    string
+		SigningToken     string
+		TLogURL          string
+		SessionTTL       time.Duration
+		ChallengeTTL     time.Duration
+		WebauthnRPID     string
+		WebauthnOrigins  string
+		AttestationIss   string
+	}{}
+	flag.StringVar(&cfg.Listen, "listen", envOr("APPROVAL_LISTEN", ":8080"), "HTTP listen address")
+	flag.StringVar(&cfg.SigningURL, "signing-url", os.Getenv("APPROVAL_SIGNING_URL"), "signing-service base URL")
+	flag.StringVar(&cfg.SigningKeyRef, "signing-key-ref", envOr("APPROVAL_SIGNING_KEY_REF", "trust-api/approval-signer-2026-q4"), "DSSE signing key reference")
+	flag.StringVar(&cfg.SigningToken, "signing-token", os.Getenv("APPROVAL_SIGNING_TOKEN"), "Bearer token for signing-service (Phase 1 static)")
+	flag.StringVar(&cfg.TLogURL, "tlog-url", os.Getenv("APPROVAL_TLOG_URL"), "transparency-log base URL")
+	flag.DurationVar(&cfg.SessionTTL, "session-ttl", envDur("APPROVAL_SESSION_TTL", 15*time.Minute), "approval session lifetime")
+	flag.DurationVar(&cfg.ChallengeTTL, "challenge-ttl", envDur("APPROVAL_CHALLENGE_TTL", 2*time.Minute), "challenge lifetime between preview and confirm")
+	flag.StringVar(&cfg.WebauthnRPID, "webauthn-rp-id", envOr("APPROVAL_WEBAUTHN_RP_ID", "trust.basicstack.de"), "WebAuthn relying party ID")
+	flag.StringVar(&cfg.WebauthnOrigins, "webauthn-origins", envOr("APPROVAL_WEBAUTHN_RP_ORIGIN", "https://trust.basicstack.de"), "comma-separated allowed WebAuthn origins")
+	flag.StringVar(&cfg.AttestationIss, "attestation-issuer", envOr("APPROVAL_POCKET_ID_ISSUER", "https://auth.basicstack.de"), "issuer embedded in attestations")
+	flag.Parse()
+
+	logger := slog.New(slog.NewJSONHandler(os.Stderr, nil))
+
+	if cfg.SigningURL == "" {
+		fatal(logger, errors.New("APPROVAL_SIGNING_URL (or -signing-url) is required"))
+	}
+	if cfg.TLogURL == "" {
+		fatal(logger, errors.New("APPROVAL_TLOG_URL (or -tlog-url) is required"))
+	}
+
+	st := store.NewMemory()
+	mgr := sessions.New(st)
+	mgr.SessionTTL = cfg.SessionTTL
+	mgr.ChallengeTTL = cfg.ChallengeTTL
+
+	signClient := signer.Client{
+		BaseURL:     cfg.SigningURL,
+		HTTPClient:  &http.Client{Timeout: 10 * time.Second},
+		TokenSource: signer.StaticToken(cfg.SigningToken),
+	}
+	tlogClient := tlog.Client{
+		BaseURL:    cfg.TLogURL,
+		HTTPClient: &http.Client{Timeout: 10 * time.Second},
+	}
+
+	orch := &service.Orchestrator{
+		Store:         st,
+		Sessions:      mgr,
+		Webauthn:      webauthn.NewStore(),
+		WebauthnCfg: webauthn.VerifyConfig{
+			RPID:           cfg.WebauthnRPID,
+			AllowedOrigins: splitAndTrim(cfg.WebauthnOrigins, ","),
+		},
+		Signer:            signClient,
+		Submitter:         tlogClient,
+		SigningKeyRef:     cfg.SigningKeyRef,
+		AttestationIssuer: cfg.AttestationIss,
+	}
+
+	server := &httpapi.Server{
+		// Phase 1 wires an "unauthenticated" dev resolver — the Pocket-ID
+		// cookie middleware (shared with admin-api) attaches in deployment.
+		// This default is deliberately noisy so misconfigured deployments
+		// fail closed rather than silently accepting anonymous callers.
+		Auth: httpapi.AuthFunc(func(_ *http.Request) (auth.Principal, error) {
+			return auth.Principal{}, errors.New("approval-service: no auth middleware mounted; wire Pocket-ID before serving traffic")
+		}),
+		Sessions:     mgr,
+		Orchestrator: orch,
+		Logger:       logger,
+	}
+
+	mux := http.NewServeMux()
+	server.Mount(mux)
+
+	logger.Info("approval-service starting",
+		"listen", cfg.Listen,
+		"signing_url", cfg.SigningURL,
+		"tlog_url", cfg.TLogURL,
+		"webauthn_rp_id", cfg.WebauthnRPID,
+	)
+	if err := http.ListenAndServe(cfg.Listen, mux); err != nil {
+		fatal(logger, err)
+	}
+}
+
+func envOr(key, fallback string) string {
+	if v := os.Getenv(key); v != "" {
+		return v
+	}
+	return fallback
+}
+
+func envDur(key string, fallback time.Duration) time.Duration {
+	v := os.Getenv(key)
+	if v == "" {
+		return fallback
+	}
+	d, err := time.ParseDuration(v)
+	if err != nil {
+		return fallback
+	}
+	return d
+}
+
+func splitAndTrim(s, sep string) []string {
+	parts := strings.Split(s, sep)
+	out := make([]string, 0, len(parts))
+	for _, p := range parts {
+		p = strings.TrimSpace(p)
+		if p != "" {
+			out = append(out, p)
+		}
+	}
+	return out
+}
+
+func fatal(logger *slog.Logger, err error) {
+	logger.Error("approval-service: fatal", "err", err)
+	os.Exit(1)
+}

services/approval-service/go.mod

@@ -0,0 +1,3 @@
+module basicstack.de/proofedmesh/services/approval-service
+
+go 1.23

services/approval-service/internal/auth/context.go

@@ -0,0 +1,62 @@
+// Package auth carries the authenticated principal across the HTTP stack
+// so handlers do not re-decode the Pocket-ID session cookie on each call.
+// The Pocket-ID verification lives in services/admin-api/internal/auth; the
+// approval-service accepts a Principal already stamped by the gateway or
+// its own future middleware wrap (Phase 2).
+package auth
+
+import (
+	"context"
+	"errors"
+)
+
+type ctxKey int
+
+const (
+	principalKey ctxKey = iota
+	sessionKey
+)
+
+// Principal is the subject identifier (Pocket-ID `sub`) of the browser user
+// driving the approval. Attestations will carry it as `performed_by.sub`.
+type Principal struct {
+	Sub    string
+	Groups []string
+}
+
+// ErrNoPrincipal is returned by MustPrincipal when the request context did
+// not carry an authenticated principal.
+var ErrNoPrincipal = errors.New("auth: request is not authenticated")
+
+// WithPrincipal returns a copy of ctx carrying p.
+func WithPrincipal(ctx context.Context, p Principal) context.Context {
+	return context.WithValue(ctx, principalKey, p)
+}
+
+// FromContext returns the Principal stamped by WithPrincipal.
+func FromContext(ctx context.Context) (Principal, bool) {
+	p, ok := ctx.Value(principalKey).(Principal)
+	return p, ok
+}
+
+// MustFromContext is a convenience that returns ErrNoPrincipal when no
+// principal is present.
+func MustFromContext(ctx context.Context) (Principal, error) {
+	p, ok := FromContext(ctx)
+	if !ok || p.Sub == "" {
+		return Principal{}, ErrNoPrincipal
+	}
+	return p, nil
+}
+
+// WithSession binds the Pocket-ID `sid` claim to ctx. Approval-sessions
+// scope themselves to the browser login via this value.
+func WithSession(ctx context.Context, sid string) context.Context {
+	return context.WithValue(ctx, sessionKey, sid)
+}
+
+// SessionFromContext returns the browser sid carried in ctx.
+func SessionFromContext(ctx context.Context) (string, bool) {
+	s, ok := ctx.Value(sessionKey).(string)
+	return s, ok && s != ""
+}

services/approval-service/internal/canonical/canonical.go

@@ -0,0 +1,105 @@
+// Package canonical implements the stable JSON serialisation the
+// approval-service uses to compute H_content. It MUST stay byte-for-byte
+// compatible with services/signing-service/internal/canonical/canonical.go
+// and services/admin-api/internal/attest/hash.go, otherwise the signing
+// service's content_hash of the Statement would not match the H_content we
+// bound into the WebAuthn challenge.
+//
+// Not a full RFC 8785 implementation: all inputs we hash are strings,
+// nulls, bools, numbers (as float64 after a json.Unmarshal round-trip), and
+// nested arrays/maps of those. encoding/json emits stable output for the
+// leaves; we only force deterministic object key ordering.
+package canonical
+
+import (
+	"bytes"
+	"crypto/sha256"
+	"encoding/hex"
+	"encoding/json"
+	"fmt"
+	"sort"
+)
+
+// SHA256Hex returns the hex-encoded SHA-256 of b.
+func SHA256Hex(b []byte) string {
+	sum := sha256.Sum256(b)
+	return hex.EncodeToString(sum[:])
+}
+
+// Marshal returns the canonical JSON encoding of v (sorted object keys).
+func Marshal(v any) ([]byte, error) {
+	first, err := json.Marshal(v)
+	if err != nil {
+		return nil, err
+	}
+	var any_ any
+	if err := json.Unmarshal(first, &any_); err != nil {
+		return nil, err
+	}
+	var buf bytes.Buffer
+	if err := writeSorted(&buf, any_); err != nil {
+		return nil, err
+	}
+	return buf.Bytes(), nil
+}
+
+// Hash returns the sha256:<hex> content hash of v's canonical JSON.
+func Hash(v any) (string, []byte, error) {
+	raw, err := Marshal(v)
+	if err != nil {
+		return "", nil, err
+	}
+	return "sha256:" + SHA256Hex(raw), raw, nil
+}
+
+func writeSorted(buf *bytes.Buffer, v any) error {
+	switch x := v.(type) {
+	case nil:
+		buf.WriteString("null")
+	case bool:
+		if x {
+			buf.WriteString("true")
+		} else {
+			buf.WriteString("false")
+		}
+	case float64:
+		b, _ := json.Marshal(x)
+		buf.Write(b)
+	case string:
+		b, _ := json.Marshal(x)
+		buf.Write(b)
+	case []any:
+		buf.WriteByte('[')
+		for i, el := range x {
+			if i > 0 {
+				buf.WriteByte(',')
+			}
+			if err := writeSorted(buf, el); err != nil {
+				return err
+			}
+		}
+		buf.WriteByte(']')
+	case map[string]any:
+		keys := make([]string, 0, len(x))
+		for k := range x {
+			keys = append(keys, k)
+		}
+		sort.Strings(keys)
+		buf.WriteByte('{')
+		for i, k := range keys {
+			if i > 0 {
+				buf.WriteByte(',')
+			}
+			kb, _ := json.Marshal(k)
+			buf.Write(kb)
+			buf.WriteByte(':')
+			if err := writeSorted(buf, x[k]); err != nil {
+				return err
+			}
+		}
+		buf.WriteByte('}')
+	default:
+		return fmt.Errorf("canonical.writeSorted: unsupported type %T", v)
+	}
+	return nil
+}

services/approval-service/internal/canonical/canonical_test.go

@@ -0,0 +1,40 @@
+package canonical
+
+import "testing"
+
+func TestMarshalSortsKeys(t *testing.T) {
+	got, err := Marshal(map[string]any{"b": 1, "a": 2})
+	if err != nil {
+		t.Fatal(err)
+	}
+	// Both keys must be present and sorted by name
+	want := `{"a":2,"b":1}`
+	if string(got) != want {
+		t.Errorf("got %q want %q", string(got), want)
+	}
+}
+
+func TestMarshalStableAcrossRuns(t *testing.T) {
+	input := map[string]any{
+		"outer": map[string]any{"z": 1, "a": 2, "m": 3},
+		"arr":   []any{"3", "1", "2"},
+	}
+	a, _ := Marshal(input)
+	b, _ := Marshal(input)
+	if string(a) != string(b) {
+		t.Errorf("not stable:\n%s\nvs\n%s", a, b)
+	}
+}
+
+func TestHashReturnsPrefix(t *testing.T) {
+	hash, raw, err := Hash(map[string]any{"k": "v"})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if hash[:7] != "sha256:" {
+		t.Errorf("hash missing sha256: prefix: %q", hash)
+	}
+	if string(raw) != `{"k":"v"}` {
+		t.Errorf("canonical form: %q", raw)
+	}
+}

services/approval-service/internal/content/binding.go

@@ -0,0 +1,117 @@
+// Package content implements the content-binding primitives of the
+// approval-service: the H_content hash of a renderable approval payload,
+// the WebAuthn challenge derivation (nonce || H_content), and the human-
+// readable verification digits an operator cross-checks against the UI.
+//
+// The *content* passed in from the HTTP handler is server-rendered JSON —
+// not the raw request payload. "Server-rendered" means we have already
+// resolved template variables, lookups, and defaults, so H_content is a
+// hash of exactly what the approving human saw. See
+// docs/architecture/v1.1.md §4.3.
+package content
+
+import (
+	"crypto/rand"
+	"crypto/sha256"
+	"encoding/binary"
+	"encoding/hex"
+	"errors"
+	"fmt"
+
+	"basicstack.de/proofedmesh/services/approval-service/internal/canonical"
+)
+
+// Phase1Rendered is the server-rendered approval payload. For Phase 1 the
+// approval-service does not own a template language — the caller hands us
+// the fully resolved object (title, bullets, action, etc.) and we hash it
+// as-is. Phase 2 will introduce typed template kinds.
+type Phase1Rendered = map[string]any
+
+// Binding is everything the preview endpoint persists so the confirm
+// endpoint can verify the WebAuthn assertion unambiguously.
+type Binding struct {
+	// ContentCanonical is the canonical JSON bytes of the rendered content.
+	ContentCanonical []byte
+	// ContentHash is "sha256:<hex>" over ContentCanonical.
+	ContentHash string
+	// Salt is 16 random bytes mixed into VerificationDigits so an attacker
+	// who guesses a content payload cannot pre-compute its digits.
+	Salt []byte
+	// Nonce is 32 random bytes forming the first half of the WebAuthn
+	// challenge; the second half is the raw sha256 of ContentCanonical.
+	Nonce []byte
+	// Challenge is Nonce || sha256(ContentCanonical). Base64url-encoded on
+	// the wire inside the WebAuthn ClientDataJSON `challenge` field.
+	Challenge []byte
+	// VerificationDigits is a short 6-digit number derived from the
+	// H_content + Salt, shown to the human for cross-checking.
+	VerificationDigits string
+}
+
+// Bind computes the full content-binding for rendered. The caller MUST
+// pass server-rendered content (NOT raw user input).
+func Bind(rendered Phase1Rendered) (Binding, error) {
+	if rendered == nil {
+		return Binding{}, errors.New("content: rendered payload is nil")
+	}
+	raw, err := canonical.Marshal(rendered)
+	if err != nil {
+		return Binding{}, fmt.Errorf("canonicalise rendered: %w", err)
+	}
+	sum := sha256.Sum256(raw)
+	salt := make([]byte, 16)
+	if _, err := rand.Read(salt); err != nil {
+		return Binding{}, fmt.Errorf("salt: %w", err)
+	}
+	nonce := make([]byte, 32)
+	if _, err := rand.Read(nonce); err != nil {
+		return Binding{}, fmt.Errorf("nonce: %w", err)
+	}
+	challenge := make([]byte, 0, len(nonce)+len(sum))
+	challenge = append(challenge, nonce...)
+	challenge = append(challenge, sum[:]...)
+	return Binding{
+		ContentCanonical:   raw,
+		ContentHash:        "sha256:" + hex.EncodeToString(sum[:]),
+		Salt:               salt,
+		Nonce:              nonce,
+		Challenge:          challenge,
+		VerificationDigits: digits(sum[:], salt),
+	}, nil
+}
+
+// RehashCanonical takes previously-stored canonical bytes and recomputes
+// the hash. Used on the confirm path to prove the preview's canonical
+// bytes still produce the expected ContentHash — defense-in-depth against
+// store tampering.
+func RehashCanonical(canonicalJSON []byte) string {
+	sum := sha256.Sum256(canonicalJSON)
+	return "sha256:" + hex.EncodeToString(sum[:])
+}
+
+// ChallengeFor returns the canonical WebAuthn challenge bytes given a
+// stored (nonce, canonicalJSON) pair. We re-derive the challenge rather
+// than storing it so a corrupted challenge column cannot smuggle an
+// attacker-chosen value into the signature path.
+func ChallengeFor(nonce, canonicalJSON []byte) []byte {
+	sum := sha256.Sum256(canonicalJSON)
+	out := make([]byte, 0, len(nonce)+len(sum))
+	out = append(out, nonce...)
+	out = append(out, sum[:]...)
+	return out
+}
+
+// digits folds H_content and salt into a 6-digit decimal code. The salt
+// prevents an attacker who knows a candidate rendered payload from pre-
+// computing the digits an operator will see.
+func digits(hContent, salt []byte) string {
+	h := sha256.New()
+	h.Write([]byte("verification-digits/v1\x00"))
+	h.Write(hContent)
+	h.Write([]byte{0x00})
+	h.Write(salt)
+	sum := h.Sum(nil)
+	// take the first 8 bytes as a big-endian uint64, mod 10^6 for 6 digits.
+	n := binary.BigEndian.Uint64(sum[:8]) % 1_000_000
+	return fmt.Sprintf("%06d", n)
+}

services/approval-service/internal/content/binding_test.go

@@ -0,0 +1,89 @@
+package content
+
+import (
+	"bytes"
+	"crypto/sha256"
+	"encoding/hex"
+	"testing"
+)
+
+func TestBindStableHash(t *testing.T) {
+	payload := Phase1Rendered{
+		"title":  "Approve policy change v3",
+		"action": "sign",
+		"detail": map[string]any{"policy_id": "pol-42"},
+	}
+	a, err := Bind(payload)
+	if err != nil {
+		t.Fatalf("Bind: %v", err)
+	}
+	b, err := Bind(payload)
+	if err != nil {
+		t.Fatalf("Bind again: %v", err)
+	}
+	if a.ContentHash != b.ContentHash {
+		t.Errorf("content_hash not stable: %q vs %q", a.ContentHash, b.ContentHash)
+	}
+	if !bytes.Equal(a.ContentCanonical, b.ContentCanonical) {
+		t.Errorf("canonical bytes not stable")
+	}
+	if bytes.Equal(a.Salt, b.Salt) {
+		t.Errorf("salt should be random (equal across two calls)")
+	}
+	if bytes.Equal(a.Nonce, b.Nonce) {
+		t.Errorf("nonce should be random (equal across two calls)")
+	}
+}
+
+func TestBindRejectsNil(t *testing.T) {
+	if _, err := Bind(nil); err == nil {
+		t.Fatalf("Bind(nil) must error")
+	}
+}
+
+func TestVerificationDigitsFormat(t *testing.T) {
+	b, err := Bind(Phase1Rendered{"k": "v"})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if l := len(b.VerificationDigits); l != 6 {
+		t.Errorf("want 6 digits, got %d (%q)", l, b.VerificationDigits)
+	}
+	for _, r := range b.VerificationDigits {
+		if r < '0' || r > '9' {
+			t.Errorf("non-digit %q in verification digits %q", r, b.VerificationDigits)
+		}
+	}
+}
+
+func TestChallengeFor_Deterministic(t *testing.T) {
+	b, err := Bind(Phase1Rendered{"k": "v"})
+	if err != nil {
+		t.Fatal(err)
+	}
+	got := ChallengeFor(b.Nonce, b.ContentCanonical)
+	if !bytes.Equal(got, b.Challenge) {
+		t.Errorf("ChallengeFor must reproduce the challenge")
+	}
+	// Flip a byte in canonical content — challenge must change.
+	alt := append([]byte(nil), b.ContentCanonical...)
+	alt[0] ^= 0xff
+	if bytes.Equal(ChallengeFor(b.Nonce, alt), b.Challenge) {
+		t.Errorf("challenge did not change when canonical content was tampered")
+	}
+}
+
+func TestRehashCanonicalMatchesBind(t *testing.T) {
+	b, err := Bind(Phase1Rendered{"foo": "bar"})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if got := RehashCanonical(b.ContentCanonical); got != b.ContentHash {
+		t.Errorf("RehashCanonical=%q want %q", got, b.ContentHash)
+	}
+	// Sanity: computed independently
+	sum := sha256.Sum256(b.ContentCanonical)
+	if "sha256:"+hex.EncodeToString(sum[:]) != b.ContentHash {
+		t.Errorf("ContentHash does not match computed sha256")
+	}
+}

services/approval-service/internal/httpapi/server.go

@@ -0,0 +1,245 @@
+// Package httpapi mounts the approval-service HTTP endpoints.
+package httpapi
+
+import (
+	"context"
+	"encoding/base64"
+	"encoding/json"
+	"errors"
+	"log/slog"
+	"net/http"
+	"time"
+
+	"basicstack.de/proofedmesh/services/approval-service/internal/auth"
+	"basicstack.de/proofedmesh/services/approval-service/internal/content"
+	"basicstack.de/proofedmesh/services/approval-service/internal/service"
+	"basicstack.de/proofedmesh/services/approval-service/internal/sessions"
+	"basicstack.de/proofedmesh/services/approval-service/internal/signer"
+	"basicstack.de/proofedmesh/services/approval-service/internal/store"
+	"basicstack.de/proofedmesh/services/approval-service/internal/webauthn"
+	pkgapi "basicstack.de/proofedmesh/services/approval-service/pkg/httpapi"
+)
+
+// AuthResolver resolves the authenticated principal from the request.
+// Prod wires it to the Pocket-ID cookie middleware; tests inject a
+// fixed principal via a shim.
+type AuthResolver interface {
+	Resolve(r *http.Request) (auth.Principal, error)
+}
+
+// AuthFunc adapts a plain function to AuthResolver.
+type AuthFunc func(r *http.Request) (auth.Principal, error)
+
+// Resolve calls f.
+func (f AuthFunc) Resolve(r *http.Request) (auth.Principal, error) { return f(r) }
+
+// Server is the HTTP handler for the approval-service.
+type Server struct {
+	Auth         AuthResolver
+	Sessions     *sessions.Manager
+	Orchestrator *service.Orchestrator
+	Logger       *slog.Logger
+	Now          func() time.Time
+}
+
+// Mount registers the three API routes plus /healthz on mux.
+func (s *Server) Mount(mux *http.ServeMux) {
+	mux.HandleFunc("POST /api/v1/sessions", s.handleCreateSession)
+	mux.HandleFunc("POST /api/v1/approvals/preview", s.handlePreview)
+	mux.HandleFunc("POST /api/v1/approvals/confirm", s.handleConfirm)
+	mux.HandleFunc("GET /healthz", s.handleHealth)
+}
+
+func (s *Server) handleHealth(w http.ResponseWriter, _ *http.Request) {
+	w.Header().Set("Content-Type", "application/json")
+	w.WriteHeader(http.StatusOK)
+	_, _ = w.Write([]byte(`{"status":"ok"}`))
+}
+
+func (s *Server) handleCreateSession(w http.ResponseWriter, r *http.Request) {
+	p, err := s.resolve(r)
+	if err != nil {
+		writeErr(w, http.StatusUnauthorized, "unauthorized", err.Error())
+		return
+	}
+	// POST /sessions has no body in Phase 1; the Pocket-ID principal
+	// alone identifies the user.
+	sess, err := s.Sessions.StartSession(r.Context(), p.Sub)
+	if err != nil {
+		s.logError("start session failed", err)
+		writeErr(w, http.StatusInternalServerError, "session_create_failed", err.Error())
+		return
+	}
+	writeJSON(w, http.StatusCreated, pkgapi.CreateSessionResponse{
+		SessionID:   sess.ID,
+		UserSub:     sess.UserSub,
+		ActiveUntil: sess.ActiveUntil,
+	})
+}
+
+func (s *Server) handlePreview(w http.ResponseWriter, r *http.Request) {
+	p, err := s.resolve(r)
+	if err != nil {
+		writeErr(w, http.StatusUnauthorized, "unauthorized", err.Error())
+		return
+	}
+	var req pkgapi.PreviewRequest
+	if err := decodeJSON(r, &req); err != nil {
+		writeErr(w, http.StatusBadRequest, "bad_request", err.Error())
+		return
+	}
+	if req.SessionID == "" {
+		writeErr(w, http.StatusBadRequest, "bad_request", "session_id is required")
+		return
+	}
+	if len(req.Content) == 0 {
+		writeErr(w, http.StatusBadRequest, "bad_request", "content is required")
+		return
+	}
+
+	sess, err := s.Sessions.GetActiveSession(r.Context(), req.SessionID, p.Sub)
+	switch {
+	case errors.Is(err, store.ErrNotFound):
+		writeErr(w, http.StatusNotFound, "session_not_found", "session_id unknown")
+		return
+	case errors.Is(err, sessions.ErrSessionExpired):
+		writeErr(w, http.StatusForbidden, "session_expired", "approval session expired")
+		return
+	case err != nil:
+		s.logError("session lookup failed", err)
+		writeErr(w, http.StatusInternalServerError, "session_lookup_failed", err.Error())
+		return
+	}
+
+	bind, err := content.Bind(req.Content)
+	if err != nil {
+		writeErr(w, http.StatusBadRequest, "bad_request", "content: "+err.Error())
+		return
+	}
+	previewID, err := s.Orchestrator.NewID("pv")
+	if err != nil {
+		writeErr(w, http.StatusInternalServerError, "id_gen_failed", err.Error())
+		return
+	}
+	now := s.now()
+	pv := store.Preview{
+		ID:                 previewID,
+		SessionID:          sess.ID,
+		UserSub:            p.Sub,
+		ContentHash:        bind.ContentHash,
+		ContentCanonical:   bind.ContentCanonical,
+		Salt:               bind.Salt,
+		Nonce:              bind.Nonce,
+		VerificationDigits: bind.VerificationDigits,
+		ExpiresAt:          now.Add(s.Sessions.ChallengeTTL),
+		CreatedAt:          now,
+	}
+	if err := s.Orchestrator.Store.SavePreview(r.Context(), pv); err != nil {
+		s.logError("save preview failed", err)
+		writeErr(w, http.StatusInternalServerError, "save_preview_failed", err.Error())
+		return
+	}
+	writeJSON(w, http.StatusOK, pkgapi.PreviewResponse{
+		PreviewID:          pv.ID,
+		ContentHash:        pv.ContentHash,
+		VerificationDigits: pv.VerificationDigits,
+		WebauthnChallenge:  base64.RawURLEncoding.EncodeToString(bind.Challenge),
+		ExpiresAt:          pv.ExpiresAt,
+	})
+}
+
+func (s *Server) handleConfirm(w http.ResponseWriter, r *http.Request) {
+	p, err := s.resolve(r)
+	if err != nil {
+		writeErr(w, http.StatusUnauthorized, "unauthorized", err.Error())
+		return
+	}
+	var req pkgapi.ConfirmRequest
+	if err := decodeJSON(r, &req); err != nil {
+		writeErr(w, http.StatusBadRequest, "bad_request", err.Error())
+		return
+	}
+	if req.PreviewID == "" {
+		writeErr(w, http.StatusBadRequest, "bad_request", "preview_id is required")
+		return
+	}
+	assertion := webauthn.Assertion(req.Assertion)
+	res, err := s.Orchestrator.Confirm(r.Context(), req.PreviewID, assertion, p.Sub)
+	if err != nil {
+		s.mapConfirmError(w, err)
+		return
+	}
+	writeJSON(w, http.StatusOK, pkgapi.ConfirmResponse{
+		ApprovalID:     res.ApprovalID,
+		AttestationRef: res.AttestationRef,
+		LogIndex:       res.LogIndex,
+		TLogStatus:     string(res.TLogStatus),
+	})
+}
+
+func (s *Server) mapConfirmError(w http.ResponseWriter, err error) {
+	switch {
+	case errors.Is(err, store.ErrNotFound):
+		writeErr(w, http.StatusNotFound, "preview_not_found", "preview_id unknown")
+	case errors.Is(err, store.ErrAlreadyConsumed):
+		writeErr(w, http.StatusConflict, "preview_consumed", "preview already consumed")
+	case errors.Is(err, service.ErrChallengeExpired):
+		writeErr(w, http.StatusForbidden, "challenge_expired", "approval challenge expired")
+	case errors.Is(err, service.ErrContentHashMismatch):
+		writeErr(w, http.StatusBadRequest, "content_hash_mismatch", err.Error())
+	case errors.Is(err, webauthn.ErrChallengeMismatch):
+		writeErr(w, http.StatusBadRequest, "content_hash_mismatch", err.Error())
+	case errors.Is(err, webauthn.ErrCredentialUnknown):
+		writeErr(w, http.StatusUnauthorized, "credential_unknown", "credential_id not registered")
+	case errors.Is(err, webauthn.ErrAssertionInvalid):
+		writeErr(w, http.StatusUnauthorized, "assertion_invalid", "webauthn assertion verification failed")
+	case errors.Is(err, signer.ErrSignerUnavailable):
+		writeErr(w, http.StatusBadGateway, "signer_unavailable", err.Error())
+	default:
+		s.logError("confirm failed", err)
+		writeErr(w, http.StatusInternalServerError, "confirm_failed", err.Error())
+	}
+}
+
+func (s *Server) resolve(r *http.Request) (auth.Principal, error) {
+	if s.Auth == nil {
+		return auth.Principal{}, errors.New("no auth resolver configured")
+	}
+	return s.Auth.Resolve(r)
+}
+
+func (s *Server) now() time.Time {
+	if s.Now != nil {
+		return s.Now()
+	}
+	return time.Now()
+}
+
+func (s *Server) logError(msg string, err error) {
+	if s.Logger != nil {
+		s.Logger.Error("approval-service: "+msg, "err", err)
+	}
+}
+
+func decodeJSON(r *http.Request, v any) error {
+	dec := json.NewDecoder(http.MaxBytesReader(nil, r.Body, 1<<20))
+	dec.DisallowUnknownFields()
+	if err := dec.Decode(v); err != nil {
+		return err
+	}
+	return nil
+}
+
+func writeJSON(w http.ResponseWriter, status int, v any) {
+	w.Header().Set("Content-Type", "application/json")
+	w.WriteHeader(status)
+	_ = json.NewEncoder(w).Encode(v)
+}
+
+func writeErr(w http.ResponseWriter, status int, code, msg string) {
+	writeJSON(w, status, pkgapi.Error{Error: pkgapi.ErrorBody{Code: code, Message: msg}})
+}
+
+// Context sanity: ensure we never return a canceled error as a 500 just
+// because the client disconnected mid-flight.
+var _ context.Context = context.Background()

services/approval-service/internal/httpapi/server_test.go

@@ -0,0 +1,463 @@
+package httpapi_test
+
+import (
+	"bytes"
+	"context"
+	"crypto/ed25519"
+	"crypto/rand"
+	"crypto/sha256"
+	"encoding/base64"
+	"encoding/json"
+	"errors"
+	"io"
+	"net/http"
+	"net/http/httptest"
+	"strings"
+	"sync"
+	"testing"
+	"time"
+
+	"basicstack.de/proofedmesh/services/approval-service/internal/auth"
+	"basicstack.de/proofedmesh/services/approval-service/internal/httpapi"
+	"basicstack.de/proofedmesh/services/approval-service/internal/service"
+	"basicstack.de/proofedmesh/services/approval-service/internal/sessions"
+	"basicstack.de/proofedmesh/services/approval-service/internal/signer"
+	"basicstack.de/proofedmesh/services/approval-service/internal/store"
+	"basicstack.de/proofedmesh/services/approval-service/internal/tlog"
+	"basicstack.de/proofedmesh/services/approval-service/internal/webauthn"
+	pkgapi "basicstack.de/proofedmesh/services/approval-service/pkg/httpapi"
+)
+
+// fixture bundles everything a test needs to drive the HTTP server.
+type fixture struct {
+	t             *testing.T
+	server        *httptest.Server
+	userSub       string
+	credID        string
+	credPriv      ed25519.PrivateKey
+	rpID          string
+	origin        string
+	fakeSigner    *fakeSigner
+	fakeTLog      *fakeTLog
+	store         *store.Memory
+}
+
+type fakeSigner struct {
+	mu            sync.Mutex
+	err           error
+	wantKeyRef    string
+	seenStatement signer.Statement
+}
+
+func (f *fakeSigner) SignDSSE(_ context.Context, keyRef string, stmt signer.Statement) (signer.Envelope, string, error) {
+	f.mu.Lock()
+	defer f.mu.Unlock()
+	if f.err != nil {
+		return signer.Envelope{}, "", f.err
+	}
+	if f.wantKeyRef != "" && keyRef != f.wantKeyRef {
+		return signer.Envelope{}, "", errors.New("unexpected keyRef")
+	}
+	f.seenStatement = stmt
+	// Produce a deterministic envelope so tests can assert on it.
+	payload := base64.RawURLEncoding.EncodeToString([]byte("payload-bytes"))
+	env := signer.Envelope{
+		PayloadType: "application/vnd.in-toto+json",
+		Payload:     payload,
+		Signatures:  []signer.EnvelopeSignature{{KeyID: keyRef, Sig: "AA"}},
+	}
+	envBytes, _ := json.Marshal(env)
+	sum := sha256.Sum256(envBytes)
+	return env, "sha256:" + hex(sum[:]), nil
+}
+
+type fakeTLog struct {
+	mu       sync.Mutex
+	err      error
+	submits  int
+	lastHash string
+}
+
+func (f *fakeTLog) Submit(_ context.Context, _ signer.Envelope, contentHash string) (tlog.Receipt, error) {
+	f.mu.Lock()
+	defer f.mu.Unlock()
+	f.submits++
+	f.lastHash = contentHash
+	if f.err != nil {
+		return tlog.Receipt{}, f.err
+	}
+	return tlog.Receipt{
+		LogIndex:    42,
+		ContentHash: contentHash,
+		LoggedAt:    time.Now().UTC(),
+	}, nil
+}
+
+// newFixture wires a Server backed by an in-memory store + fakes. A single
+// WebAuthn credential is pre-registered for userSub so tests can confirm
+// previews without going through a real enrollment ceremony.
+func newFixture(t *testing.T, opts ...func(*service.Orchestrator)) *fixture {
+	t.Helper()
+	st := store.NewMemory()
+	mgr := sessions.New(st)
+	mgr.SessionTTL = 15 * time.Minute
+	mgr.ChallengeTTL = 2 * time.Minute
+
+	userSub := "user-alice"
+	pub, priv, err := ed25519.GenerateKey(rand.Reader)
+	if err != nil {
+		t.Fatalf("gen key: %v", err)
+	}
+	idBytes := make([]byte, 16)
+	_, _ = rand.Read(idBytes)
+	credID := base64.RawURLEncoding.EncodeToString(idBytes)
+	webStore := webauthn.NewStore()
+	if err := webStore.AddCredential(webauthn.Credential{
+		ID:        credID,
+		UserSub:   userSub,
+		PublicKey: pub,
+	}); err != nil {
+		t.Fatalf("register credential: %v", err)
+	}
+
+	rpID := "trust.basicstack.de"
+	origin := "https://trust.basicstack.de"
+
+	sig := &fakeSigner{wantKeyRef: "trust-api/approval-signer-2026-q4"}
+	submitter := &fakeTLog{}
+
+	orch := &service.Orchestrator{
+		Store:    st,
+		Sessions: mgr,
+		Webauthn: webStore,
+		WebauthnCfg: webauthn.VerifyConfig{
+			RPID:           rpID,
+			AllowedOrigins: []string{origin},
+		},
+		Signer:            sig,
+		Submitter:         submitter,
+		SigningKeyRef:     "trust-api/approval-signer-2026-q4",
+		AttestationIssuer: "https://auth.basicstack.de",
+	}
+	for _, o := range opts {
+		o(orch)
+	}
+
+	srv := &httpapi.Server{
+		Auth: httpapi.AuthFunc(func(_ *http.Request) (auth.Principal, error) {
+			return auth.Principal{Sub: userSub, Groups: []string{"proofedmesh-admin"}}, nil
+		}),
+		Sessions:     mgr,
+		Orchestrator: orch,
+	}
+	mux := http.NewServeMux()
+	srv.Mount(mux)
+	ts := httptest.NewServer(mux)
+	t.Cleanup(ts.Close)
+
+	return &fixture{
+		t:          t,
+		server:     ts,
+		userSub:    userSub,
+		credID:     credID,
+		credPriv:   priv,
+		rpID:       rpID,
+		origin:     origin,
+		fakeSigner: sig,
+		fakeTLog:   submitter,
+		store:      st,
+	}
+}
+
+func (f *fixture) startSession() pkgapi.CreateSessionResponse {
+	f.t.Helper()
+	var out pkgapi.CreateSessionResponse
+	f.do("POST", "/api/v1/sessions", nil, http.StatusCreated, &out)
+	return out
+}
+
+func (f *fixture) preview(sessionID string, content map[string]any, want int) pkgapi.PreviewResponse {
+	f.t.Helper()
+	var out pkgapi.PreviewResponse
+	f.do("POST", "/api/v1/approvals/preview", pkgapi.PreviewRequest{
+		SessionID: sessionID,
+		Content:   content,
+	}, want, &out)
+	return out
+}
+
+func (f *fixture) confirm(req pkgapi.ConfirmRequest, want int) (*pkgapi.ConfirmResponse, *pkgapi.Error) {
+	f.t.Helper()
+	resp := f.doRaw("POST", "/api/v1/approvals/confirm", req)
+	defer resp.Body.Close()
+	body, _ := io.ReadAll(resp.Body)
+	if resp.StatusCode != want {
+		f.t.Fatalf("confirm: status %d want %d: %s", resp.StatusCode, want, string(body))
+	}
+	if want >= 200 && want < 300 {
+		var out pkgapi.ConfirmResponse
+		if err := json.Unmarshal(body, &out); err != nil {
+			f.t.Fatalf("decode confirm: %v (%s)", err, string(body))
+		}
+		return &out, nil
+	}
+	var ebody pkgapi.Error
+	if err := json.Unmarshal(body, &ebody); err != nil {
+		f.t.Fatalf("decode confirm error: %v (%s)", err, string(body))
+	}
+	return nil, &ebody
+}
+
+func (f *fixture) do(method, path string, body any, want int, out any) {
+	f.t.Helper()
+	resp := f.doRaw(method, path, body)
+	defer resp.Body.Close()
+	raw, _ := io.ReadAll(resp.Body)
+	if resp.StatusCode != want {
+		f.t.Fatalf("%s %s: status %d want %d: %s", method, path, resp.StatusCode, want, string(raw))
+	}
+	if out != nil {
+		if err := json.Unmarshal(raw, out); err != nil {
+			f.t.Fatalf("decode %s: %v (%s)", path, err, string(raw))
+		}
+	}
+}
+
+func (f *fixture) doRaw(method, path string, body any) *http.Response {
+	f.t.Helper()
+	var r io.Reader
+	if body != nil {
+		b, err := json.Marshal(body)
+		if err != nil {
+			f.t.Fatalf("marshal body: %v", err)
+		}
+		r = bytes.NewReader(b)
+	}
+	req, err := http.NewRequest(method, f.server.URL+path, r)
+	if err != nil {
+		f.t.Fatalf("new request: %v", err)
+	}
+	if body != nil {
+		req.Header.Set("Content-Type", "application/json")
+	}
+	resp, err := f.server.Client().Do(req)
+	if err != nil {
+		f.t.Fatalf("do: %v", err)
+	}
+	return resp
+}
+
+func (f *fixture) signAssertion(challenge []byte) pkgapi.Assertion {
+	f.t.Helper()
+	cd := map[string]string{
+		"type":      "webauthn.get",
+		"challenge": base64.RawURLEncoding.EncodeToString(challenge),
+		"origin":    f.origin,
+	}
+	cdBytes, _ := json.Marshal(cd)
+	authData := webauthn.MakeAuthenticatorData(f.rpID)
+	cdHash := sha256.Sum256(cdBytes)
+	signed := append(append([]byte(nil), authData...), cdHash[:]...)
+	sig := ed25519.Sign(f.credPriv, signed)
+	return pkgapi.Assertion{
+		CredentialID:      f.credID,
+		ClientDataJSON:    base64.RawURLEncoding.EncodeToString(cdBytes),
+		AuthenticatorData: base64.RawURLEncoding.EncodeToString(authData),
+		Signature:         base64.RawURLEncoding.EncodeToString(sig),
+	}
+}
+
+func hex(b []byte) string {
+	const hexchars = "0123456789abcdef"
+	out := make([]byte, len(b)*2)
+	for i, c := range b {
+		out[i*2] = hexchars[c>>4]
+		out[i*2+1] = hexchars[c&0x0f]
+	}
+	return string(out)
+}
+
+// --- actual tests ---------------------------------------------------------
+
+func TestHappyPath(t *testing.T) {
+	f := newFixture(t)
+	sess := f.startSession()
+	if sess.SessionID == "" {
+		t.Fatalf("no session_id returned")
+	}
+	if sess.UserSub != f.userSub {
+		t.Errorf("session.user_sub = %q want %q", sess.UserSub, f.userSub)
+	}
+
+	pv := f.preview(sess.SessionID, map[string]any{
+		"title":  "Approve rate change",
+		"action": "sign",
+	}, http.StatusOK)
+	if !strings.HasPrefix(pv.ContentHash, "sha256:") {
+		t.Errorf("preview content_hash: %q", pv.ContentHash)
+	}
+	if pv.VerificationDigits == "" {
+		t.Errorf("empty verification digits")
+	}
+
+	challenge, err := base64.RawURLEncoding.DecodeString(pv.WebauthnChallenge)
+	if err != nil {
+		t.Fatalf("decode challenge: %v", err)
+	}
+	assertion := f.signAssertion(challenge)
+	ok, _ := f.confirm(pkgapi.ConfirmRequest{PreviewID: pv.PreviewID, Assertion: assertion}, http.StatusOK)
+	if ok.TLogStatus != "logged" {
+		t.Errorf("tlog status: %q want logged", ok.TLogStatus)
+	}
+	if ok.LogIndex == nil || *ok.LogIndex != 42 {
+		t.Errorf("log_index = %v want 42", ok.LogIndex)
+	}
+	if ok.AttestationRef == "" || !strings.HasPrefix(ok.AttestationRef, "sha256:") {
+		t.Errorf("attestation_ref: %q", ok.AttestationRef)
+	}
+
+	// Assert the signer saw a Statement whose subject.digest.sha256 is
+	// the H_content of the preview (no "sha256:" prefix per in-toto).
+	f.fakeSigner.mu.Lock()
+	stmt := f.fakeSigner.seenStatement
+	f.fakeSigner.mu.Unlock()
+	subj, _ := stmt["subject"].([]any)
+	if len(subj) != 1 {
+		t.Fatalf("statement subject: %+v", subj)
+	}
+	first, _ := subj[0].(map[string]any)
+	digest, _ := first["digest"].(map[string]any)
+	gotDigest, _ := digest["sha256"].(string)
+	wantDigest := strings.TrimPrefix(pv.ContentHash, "sha256:")
+	if gotDigest != wantDigest {
+		t.Errorf("signed subject digest=%q want %q", gotDigest, wantDigest)
+	}
+}
+
+func TestConfirm_TamperedHContent(t *testing.T) {
+	f := newFixture(t)
+	sess := f.startSession()
+	pv := f.preview(sess.SessionID, map[string]any{"k": "v"}, http.StatusOK)
+
+	challenge, _ := base64.RawURLEncoding.DecodeString(pv.WebauthnChallenge)
+	// Flip the last byte of the challenge (equivalent to signing with a
+	// different H_content), the signature will be over wrong data.
+	tampered := append([]byte(nil), challenge...)
+	tampered[len(tampered)-1] ^= 0xff
+	assertion := f.signAssertion(tampered)
+	_, errBody := f.confirm(pkgapi.ConfirmRequest{PreviewID: pv.PreviewID, Assertion: assertion}, http.StatusBadRequest)
+	if errBody.Error.Code != "content_hash_mismatch" {
+		t.Errorf("error code = %q want content_hash_mismatch", errBody.Error.Code)
+	}
+}
+
+func TestConfirm_ExpiredChallenge(t *testing.T) {
+	// Force a short challenge TTL so we can race the clock.
+	f := newFixture(t)
+	sess := f.startSession()
+	pv := f.preview(sess.SessionID, map[string]any{"k": "v"}, http.StatusOK)
+
+	// Walk the preview's ExpiresAt backward directly in the store to
+	// simulate an expired challenge without a sleep.
+	prev, err := f.store.GetPreview(context.Background(), pv.PreviewID)
+	if err != nil {
+		t.Fatalf("GetPreview: %v", err)
+	}
+	prev.ExpiresAt = time.Now().Add(-1 * time.Second)
+	if err := f.store.SavePreview(context.Background(), prev); err != nil {
+		t.Fatalf("SavePreview: %v", err)
+	}
+
+	challenge, _ := base64.RawURLEncoding.DecodeString(pv.WebauthnChallenge)
+	assertion := f.signAssertion(challenge)
+	_, errBody := f.confirm(pkgapi.ConfirmRequest{PreviewID: pv.PreviewID, Assertion: assertion}, http.StatusForbidden)
+	if errBody.Error.Code != "challenge_expired" {
+		t.Errorf("error code = %q want challenge_expired", errBody.Error.Code)
+	}
+}
+
+func TestConfirm_SignerUnavailable(t *testing.T) {
+	f := newFixture(t, func(o *service.Orchestrator) {
+		o.Signer = &fakeSigner{err: signer.ErrSignerUnavailable}
+	})
+	sess := f.startSession()
+	pv := f.preview(sess.SessionID, map[string]any{"k": "v"}, http.StatusOK)
+
+	challenge, _ := base64.RawURLEncoding.DecodeString(pv.WebauthnChallenge)
+	assertion := f.signAssertion(challenge)
+	_, errBody := f.confirm(pkgapi.ConfirmRequest{PreviewID: pv.PreviewID, Assertion: assertion}, http.StatusBadGateway)
+	if errBody.Error.Code != "signer_unavailable" {
+		t.Errorf("error code = %q want signer_unavailable", errBody.Error.Code)
+	}
+}
+
+func TestConfirm_TLogFailureStaysPending(t *testing.T) {
+	f := newFixture(t, func(o *service.Orchestrator) {
+		o.Submitter = &fakeTLog{err: tlog.ErrTLogUnavailable}
+	})
+	sess := f.startSession()
+	pv := f.preview(sess.SessionID, map[string]any{"k": "v"}, http.StatusOK)
+
+	challenge, _ := base64.RawURLEncoding.DecodeString(pv.WebauthnChallenge)
+	assertion := f.signAssertion(challenge)
+	ok, _ := f.confirm(pkgapi.ConfirmRequest{PreviewID: pv.PreviewID, Assertion: assertion}, http.StatusOK)
+	if ok.TLogStatus != "attestation-pending" {
+		t.Errorf("tlog status = %q want attestation-pending", ok.TLogStatus)
+	}
+	if ok.LogIndex != nil {
+		t.Errorf("log_index = %v want nil", ok.LogIndex)
+	}
+	// Approval must still have been persisted.
+	appr, ok2 := f.store.GetApproval(ok.ApprovalID)
+	if !ok2 {
+		t.Fatalf("approval not persisted after tlog failure")
+	}
+	if appr.TLogStatus != store.TLogPending {
+		t.Errorf("stored tlog status = %q want attestation-pending", appr.TLogStatus)
+	}
+	if appr.TLogError == "" {
+		t.Errorf("expected tlog_error to be recorded")
+	}
+}
+
+func TestPreview_SessionExpired(t *testing.T) {
+	f := newFixture(t)
+	sess := f.startSession()
+	// Simulate session expiry.
+	raw, err := f.store.GetSession(context.Background(), sess.SessionID)
+	if err != nil {
+		t.Fatalf("GetSession: %v", err)
+	}
+	raw.ActiveUntil = time.Now().Add(-1 * time.Second)
+	if err := f.store.CreateSession(context.Background(), raw); err != nil {
+		t.Fatalf("CreateSession: %v", err)
+	}
+	resp := f.doRaw("POST", "/api/v1/approvals/preview", pkgapi.PreviewRequest{
+		SessionID: sess.SessionID,
+		Content:   map[string]any{"k": "v"},
+	})
+	defer resp.Body.Close()
+	raw2, _ := io.ReadAll(resp.Body)
+	if resp.StatusCode != http.StatusForbidden {
+		t.Fatalf("status %d want 403: %s", resp.StatusCode, raw2)
+	}
+	var ebody pkgapi.Error
+	_ = json.Unmarshal(raw2, &ebody)
+	if ebody.Error.Code != "session_expired" {
+		t.Errorf("error code = %q want session_expired", ebody.Error.Code)
+	}
+}
+
+func TestConfirm_PreviewConsumedTwice(t *testing.T) {
+	f := newFixture(t)
+	sess := f.startSession()
+	pv := f.preview(sess.SessionID, map[string]any{"k": "v"}, http.StatusOK)
+	challenge, _ := base64.RawURLEncoding.DecodeString(pv.WebauthnChallenge)
+	assertion := f.signAssertion(challenge)
+	_, _ = f.confirm(pkgapi.ConfirmRequest{PreviewID: pv.PreviewID, Assertion: assertion}, http.StatusOK)
+	// Second confirm must be refused.
+	_, errBody := f.confirm(pkgapi.ConfirmRequest{PreviewID: pv.PreviewID, Assertion: assertion}, http.StatusConflict)
+	if errBody.Error.Code != "preview_consumed" {
+		t.Errorf("error code = %q want preview_consumed", errBody.Error.Code)
+	}
+}

services/approval-service/internal/service/orchestrator.go

@@ -0,0 +1,236 @@
+// Package service wires the approval pipeline components (sessions,
+// content binding, webauthn, DSSE signing, Transparency Log) into one
+// Confirm orchestrator. Keeping it HTTP-free lets unit tests drive the
+// whole flow without an httptest server.
+package service
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"time"
+
+	"basicstack.de/proofedmesh/services/approval-service/internal/content"
+	"basicstack.de/proofedmesh/services/approval-service/internal/sessions"
+	"basicstack.de/proofedmesh/services/approval-service/internal/signer"
+	"basicstack.de/proofedmesh/services/approval-service/internal/store"
+	"basicstack.de/proofedmesh/services/approval-service/internal/tlog"
+	"basicstack.de/proofedmesh/services/approval-service/internal/webauthn"
+)
+
+// Signer is the signing-service client the orchestrator depends on.
+type Signer interface {
+	SignDSSE(ctx context.Context, keyRef string, stmt signer.Statement) (signer.Envelope, string, error)
+}
+
+// Submitter is the transparency-log client the orchestrator depends on.
+type Submitter interface {
+	Submit(ctx context.Context, env signer.Envelope, contentHash string) (tlog.Receipt, error)
+}
+
+// Orchestrator holds everything a Confirm needs. Fields are populated
+// from main.go; the HTTP handler just calls Confirm.
+type Orchestrator struct {
+	Store         store.Store
+	Sessions      *sessions.Manager
+	Webauthn      *webauthn.Store
+	WebauthnCfg   webauthn.VerifyConfig
+	Signer        Signer
+	Submitter     Submitter
+	SigningKeyRef string
+	// AttestationIssuer is embedded as predicate.performed_by.iss so
+	// verifiers can match the approval against our Pocket-ID issuer.
+	AttestationIssuer string
+	Now               func() time.Time
+	GenID             sessions.IDGenerator
+}
+
+// ErrContentHashMismatch is surfaced by Confirm when the preview's
+// stored canonical content no longer hashes to its stored content_hash
+// (store corruption) OR when the webauthn challenge the browser signed
+// does not match the challenge we expected for this preview. In both
+// cases the HTTP layer returns 400 per DEV-608.
+var ErrContentHashMismatch = errors.New("service: content hash mismatch")
+
+// ErrChallengeExpired is surfaced by Confirm when the preview's
+// expires_at is in the past. The HTTP layer returns 403.
+var ErrChallengeExpired = errors.New("service: challenge expired")
+
+// ConfirmResult is what Confirm returns to the HTTP handler.
+type ConfirmResult struct {
+	ApprovalID     string
+	AttestationRef string
+	LogIndex       *int64
+	TLogStatus     store.TLogStatus
+}
+
+// Confirm runs the full end-of-pipeline sequence:
+//
+//  1. Load the preview (must exist, must not be consumed, must still be
+//     within expires_at).
+//  2. Re-derive the WebAuthn challenge from the stored (nonce,
+//     canonical) and verify the assertion against it.
+//  3. Build the DSSE Statement with H_content as the subject digest.
+//  4. Call the signing-service.
+//  5. Persist the Approval row (status = attestation-pending).
+//  6. Submit to the Transparency Log. On success, flip status to
+//     "logged" and attach log_index. On TLog failure, leave the row at
+//     attestation-pending so the reconciler can retry; the HTTP response
+//     still returns ApprovalID + attestation_ref so the UI can carry on.
+//
+// The order (persist → submit) is deliberate: we never return a
+// log_index to the caller for an approval that was not durably stored,
+// and we never lose a signed envelope because we failed to log it.
+func (o *Orchestrator) Confirm(ctx context.Context, previewID string, assertion webauthn.Assertion, userSub string) (ConfirmResult, error) {
+	if previewID == "" {
+		return ConfirmResult{}, errors.New("service: previewID is empty")
+	}
+	if userSub == "" {
+		return ConfirmResult{}, errors.New("service: userSub is empty")
+	}
+	now := o.now()
+
+	pv, err := o.Store.GetPreview(ctx, previewID)
+	if err != nil {
+		return ConfirmResult{}, err
+	}
+	if pv.UserSub != userSub {
+		return ConfirmResult{}, store.ErrNotFound
+	}
+	if pv.ConsumedAt != nil {
+		return ConfirmResult{}, store.ErrAlreadyConsumed
+	}
+	if !now.Before(pv.ExpiresAt) {
+		return ConfirmResult{}, ErrChallengeExpired
+	}
+
+	// Defense-in-depth: recompute H_content from the stored canonical
+	// content and make sure it still equals the stored content_hash.
+	if content.RehashCanonical(pv.ContentCanonical) != pv.ContentHash {
+		return ConfirmResult{}, fmt.Errorf("%w: stored canonical content does not match stored content_hash", ErrContentHashMismatch)
+	}
+
+	expectedChallenge := content.ChallengeFor(pv.Nonce, pv.ContentCanonical)
+	cred, err := webauthn.Verify(o.WebauthnCfg, o.Webauthn, assertion, expectedChallenge)
+	if err != nil {
+		if errors.Is(err, webauthn.ErrChallengeMismatch) {
+			return ConfirmResult{}, fmt.Errorf("%w: %v", ErrContentHashMismatch, err)
+		}
+		return ConfirmResult{}, err
+	}
+	if cred.UserSub != userSub {
+		return ConfirmResult{}, webauthn.ErrAssertionInvalid
+	}
+
+	// Atomically mark the preview consumed so a parallel confirm cannot
+	// reuse the same signed envelope. If this fails ErrAlreadyConsumed
+	// we lose the race and must not continue.
+	if _, err := o.Store.ConsumePreview(ctx, pv.ID, now); err != nil {
+		return ConfirmResult{}, err
+	}
+
+	stmt := buildStatement(pv, userSub, o.AttestationIssuer, now)
+	env, envHash, err := o.Signer.SignDSSE(ctx, o.SigningKeyRef, stmt)
+	if err != nil {
+		return ConfirmResult{}, err
+	}
+
+	approvalID, err := o.genID("ap")
+	if err != nil {
+		return ConfirmResult{}, err
+	}
+
+	appr := store.Approval{
+		ID:             approvalID,
+		PreviewID:      pv.ID,
+		SessionID:      pv.SessionID,
+		UserSub:        userSub,
+		ContentHash:    pv.ContentHash,
+		Envelope:       env,
+		AttestationRef: envHash,
+		TLogStatus:     store.TLogPending,
+		ConfirmedAt:    now,
+	}
+	if err := o.Store.SaveApproval(ctx, appr); err != nil {
+		return ConfirmResult{}, err
+	}
+
+	receipt, submitErr := o.Submitter.Submit(ctx, env, envHash)
+	if submitErr != nil {
+		// Approval row stays at attestation-pending; record the error
+		// for diagnostics but return success-with-pending to the client.
+		_ = o.Store.MarkApprovalTLogError(ctx, approvalID, submitErr.Error())
+		return ConfirmResult{
+			ApprovalID:     approvalID,
+			AttestationRef: envHash,
+			TLogStatus:     store.TLogPending,
+		}, nil
+	}
+	loggedAt := receipt.LoggedAt
+	if loggedAt.IsZero() {
+		loggedAt = now
+	}
+	if err := o.Store.MarkApprovalLogged(ctx, approvalID, receipt.LogIndex, loggedAt); err != nil {
+		return ConfirmResult{}, err
+	}
+	idx := receipt.LogIndex
+	return ConfirmResult{
+		ApprovalID:     approvalID,
+		AttestationRef: envHash,
+		LogIndex:       &idx,
+		TLogStatus:     store.TLogLogged,
+	}, nil
+}
+
+func (o *Orchestrator) now() time.Time {
+	if o.Now != nil {
+		return o.Now()
+	}
+	return time.Now()
+}
+
+// NewID returns an opaque ID with the given prefix. Exposed so the HTTP
+// layer can mint preview_ids with the same injectable generator.
+func (o *Orchestrator) NewID(prefix string) (string, error) {
+	if o.GenID != nil {
+		return o.GenID(prefix)
+	}
+	return sessions.DefaultIDGenerator(prefix)
+}
+
+func (o *Orchestrator) genID(prefix string) (string, error) { return o.NewID(prefix) }
+
+// buildStatement renders the in-toto v1 Statement for an approval. The
+// subject.digest IS the H_content of the preview; verifiers rehash the
+// stored canonical content to prove the signature covers it.
+func buildStatement(pv store.Preview, userSub, issuer string, performedAt time.Time) signer.Statement {
+	// Strip the "sha256:" prefix for the digest map, per in-toto convention.
+	digest := pv.ContentHash
+	if len(digest) > 7 && digest[:7] == "sha256:" {
+		digest = digest[7:]
+	}
+	predicate := map[string]any{
+		"approval_schema": "basicstack.de/attestations/approval/v1",
+		"preview_id":      pv.ID,
+		"session_id":      pv.SessionID,
+		"content_hash":    pv.ContentHash,
+		"performed_by": map[string]any{
+			"iss":        issuer,
+			"sub":        userSub,
+			"session_id": pv.SessionID,
+		},
+		"performed_at":        performedAt.UTC().Format(time.RFC3339),
+		"verification_digits": pv.VerificationDigits,
+	}
+	return signer.Statement{
+		"_type": "https://in-toto.io/Statement/v1",
+		"subject": []any{
+			map[string]any{
+				"name":   "approval/" + pv.ID,
+				"digest": map[string]any{"sha256": digest},
+			},
+		},
+		"predicateType": "https://basicstack.de/attestations/approval/v1",
+		"predicate":     predicate,
+	}
+}

services/approval-service/internal/sessions/sessions.go

@@ -0,0 +1,97 @@
+// Package sessions implements the Session → Preview → Confirm pipeline on
+// top of a Store. Keeping it one layer above the HTTP handlers lets the
+// unit tests exercise business logic without an httptest server.
+package sessions
+
+import (
+	"context"
+	"crypto/rand"
+	"encoding/base64"
+	"errors"
+	"fmt"
+	"time"
+
+	"basicstack.de/proofedmesh/services/approval-service/internal/store"
+)
+
+// IDGenerator returns opaque collision-resistant IDs. The default
+// implementation uses crypto/rand; tests inject a deterministic one.
+type IDGenerator func(prefix string) (string, error)
+
+// DefaultIDGenerator produces "<prefix>_" + 24 random base64url chars.
+func DefaultIDGenerator(prefix string) (string, error) {
+	b := make([]byte, 18)
+	if _, err := rand.Read(b); err != nil {
+		return "", fmt.Errorf("id: %w", err)
+	}
+	return prefix + "_" + base64.RawURLEncoding.EncodeToString(b), nil
+}
+
+// Manager orchestrates sessions on top of a Store. Its only state is the
+// clock and ID generator; all persistence happens through Store.
+type Manager struct {
+	Store       store.Store
+	Now         func() time.Time
+	GenID       IDGenerator
+	SessionTTL  time.Duration
+	ChallengeTTL time.Duration
+}
+
+// New constructs a Manager with safe defaults for Now, GenID, SessionTTL
+// (15m) and ChallengeTTL (2m) when the caller leaves them zero.
+func New(s store.Store) *Manager {
+	return &Manager{
+		Store:        s,
+		Now:          time.Now,
+		GenID:        DefaultIDGenerator,
+		SessionTTL:   15 * time.Minute,
+		ChallengeTTL: 2 * time.Minute,
+	}
+}
+
+// StartSession creates a fresh approval_session for userSub.
+func (m *Manager) StartSession(ctx context.Context, userSub string) (store.Session, error) {
+	if userSub == "" {
+		return store.Session{}, errors.New("sessions: userSub is empty")
+	}
+	id, err := m.GenID("sess")
+	if err != nil {
+		return store.Session{}, err
+	}
+	now := m.Now()
+	s := store.Session{
+		ID:          id,
+		UserSub:     userSub,
+		ActiveUntil: now.Add(m.SessionTTL),
+		CreatedAt:   now,
+	}
+	if err := m.Store.CreateSession(ctx, s); err != nil {
+		return store.Session{}, err
+	}
+	return s, nil
+}
+
+// ErrSessionExpired is returned by GetActiveSession when the session
+// row exists but active_until is in the past.
+var ErrSessionExpired = errors.New("sessions: session expired")
+
+// GetActiveSession returns the session when it is still within
+// active_until. Enforces session_id ↔ user_sub binding (the caller passes
+// the authenticated userSub so a leaked session_id cannot be used from
+// another account).
+func (m *Manager) GetActiveSession(ctx context.Context, sessionID, userSub string) (store.Session, error) {
+	s, err := m.Store.GetSession(ctx, sessionID)
+	if err != nil {
+		return store.Session{}, err
+	}
+	if s.UserSub != userSub {
+		// Explicit NotFound so handlers return 404 instead of leaking the
+		// mismatch — a probing attacker cannot distinguish "wrong user"
+		// from "unknown session".
+		return store.Session{}, store.ErrNotFound
+	}
+	if !m.Now().Before(s.ActiveUntil) {
+		return store.Session{}, ErrSessionExpired
+	}
+	return s, nil
+}

services/approval-service/internal/sessions/sessions_test.go

@@ -0,0 +1,59 @@
+package sessions
+
+import (
+	"context"
+	"errors"
+	"testing"
+	"time"
+
+	"basicstack.de/proofedmesh/services/approval-service/internal/store"
+)
+
+func TestStartSession_UsesTTL(t *testing.T) {
+	st := store.NewMemory()
+	m := New(st)
+	m.SessionTTL = 5 * time.Minute
+	m.Now = func() time.Time { return time.Date(2026, 1, 1, 12, 0, 0, 0, time.UTC) }
+	s, err := m.StartSession(context.Background(), "alice")
+	if err != nil {
+		t.Fatalf("StartSession: %v", err)
+	}
+	want := time.Date(2026, 1, 1, 12, 5, 0, 0, time.UTC)
+	if !s.ActiveUntil.Equal(want) {
+		t.Errorf("ActiveUntil = %v want %v", s.ActiveUntil, want)
+	}
+	if s.UserSub != "alice" {
+		t.Errorf("UserSub = %q", s.UserSub)
+	}
+}
+
+func TestGetActiveSession_WrongUser(t *testing.T) {
+	st := store.NewMemory()
+	m := New(st)
+	m.Now = func() time.Time { return time.Date(2026, 1, 1, 12, 0, 0, 0, time.UTC) }
+	s, err := m.StartSession(context.Background(), "alice")
+	if err != nil {
+		t.Fatalf("StartSession: %v", err)
+	}
+	_, err = m.GetActiveSession(context.Background(), s.ID, "bob")
+	if !errors.Is(err, store.ErrNotFound) {
+		t.Fatalf("want ErrNotFound, got %v", err)
+	}
+}
+
+func TestGetActiveSession_Expired(t *testing.T) {
+	st := store.NewMemory()
+	m := New(st)
+	m.SessionTTL = time.Minute
+	t0 := time.Date(2026, 1, 1, 12, 0, 0, 0, time.UTC)
+	m.Now = func() time.Time { return t0 }
+	s, err := m.StartSession(context.Background(), "alice")
+	if err != nil {
+		t.Fatal(err)
+	}
+	m.Now = func() time.Time { return t0.Add(2 * time.Minute) }
+	_, err = m.GetActiveSession(context.Background(), s.ID, "alice")
+	if !errors.Is(err, ErrSessionExpired) {
+		t.Fatalf("want ErrSessionExpired, got %v", err)
+	}
+}

services/approval-service/internal/signer/signer.go

@@ -0,0 +1,134 @@
+// Package signer calls the signing-service's POST /api/v1/sign/dsse
+// endpoint per ADR-0005. The wire types are duplicated here (not imported
+// from the signing-service's internal package) so the approval-service
+// stays an independent module.
+package signer
+
+import (
+	"bytes"
+	"context"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"io"
+	"net/http"
+	"net/url"
+	"time"
+)
+
+// Statement is the in-toto v1 Statement handed to the signing-service.
+// Loosely typed via `map[string]any` so arbitrary predicate payloads can
+// flow through without an approval-service-local schema definition.
+type Statement map[string]any
+
+// EnvelopeSignature mirrors the DSSE spec.
+type EnvelopeSignature struct {
+	KeyID string `json:"keyid"`
+	Sig   string `json:"sig"`
+}
+
+// Envelope is the DSSE envelope returned by the signing-service.
+type Envelope struct {
+	PayloadType string              `json:"payloadType"`
+	Payload     string              `json:"payload"`
+	Signatures  []EnvelopeSignature `json:"signatures"`
+}
+
+// TokenSource supplies the Bearer token the signing-service expects. The
+// production wiring will plug in a Pocket-ID client-credentials source;
+// tests use StaticToken.
+type TokenSource interface {
+	Token(ctx context.Context) (string, error)
+}
+
+// StaticToken is a trivial constant TokenSource.
+type StaticToken string
+
+// Token returns s.
+func (s StaticToken) Token(_ context.Context) (string, error) { return string(s), nil }
+
+// ErrSignerUnavailable is returned when the signing-service refuses the
+// connection, times out, or answers 5xx. The HTTP layer maps this to 502
+// as DEV-608 requires.
+var ErrSignerUnavailable = errors.New("signer: signing-service unavailable")
+
+// Client is the DSSE sign client.
+type Client struct {
+	BaseURL     string
+	HTTPClient  *http.Client
+	TokenSource TokenSource
+}
+
+type signRequest struct {
+	KeyRef    string    `json:"key_ref"`
+	Statement Statement `json:"statement"`
+}
+
+type signResponse struct {
+	Envelope    Envelope  `json:"envelope"`
+	ContentHash string    `json:"content_hash"`
+	SignedAt    time.Time `json:"signed_at"`
+}
+
+// SignDSSE calls the signing-service and returns the DSSE envelope plus
+// its content hash. A connection-level or 5xx response from the signing-
+// service is reported as ErrSignerUnavailable.
+func (c Client) SignDSSE(ctx context.Context, keyRef string, stmt Statement) (Envelope, string, error) {
+	if c.BaseURL == "" {
+		return Envelope{}, "", errors.New("signer.Client: BaseURL is empty")
+	}
+	hc := c.HTTPClient
+	if hc == nil {
+		hc = &http.Client{Timeout: 10 * time.Second}
+	}
+	body, err := json.Marshal(signRequest{KeyRef: keyRef, Statement: stmt})
+	if err != nil {
+		return Envelope{}, "", fmt.Errorf("marshal sign request: %w", err)
+	}
+	endpoint, err := url.JoinPath(c.BaseURL, "/api/v1/sign/dsse")
+	if err != nil {
+		return Envelope{}, "", fmt.Errorf("join signing-service url: %w", err)
+	}
+	req, err := http.NewRequestWithContext(ctx, http.MethodPost, endpoint, bytes.NewReader(body))
+	if err != nil {
+		return Envelope{}, "", err
+	}
+	req.Header.Set("Content-Type", "application/json")
+	req.Header.Set("Accept", "application/json")
+	if c.TokenSource != nil {
+		tok, err := c.TokenSource.Token(ctx)
+		if err != nil {
+			return Envelope{}, "", fmt.Errorf("token: %w", err)
+		}
+		if tok != "" {
+			req.Header.Set("Authorization", "Bearer "+tok)
+		}
+	}
+	resp, err := hc.Do(req)
+	if err != nil {
+		return Envelope{}, "", fmt.Errorf("%w: %v", ErrSignerUnavailable, err)
+	}
+	defer resp.Body.Close()
+	raw, _ := io.ReadAll(io.LimitReader(resp.Body, 1<<20))
+	if resp.StatusCode >= 500 {
+		return Envelope{}, "", fmt.Errorf("%w: status %d: %s", ErrSignerUnavailable, resp.StatusCode, truncate(raw, 256))
+	}
+	if resp.StatusCode != http.StatusOK {
+		return Envelope{}, "", fmt.Errorf("signer: status %d: %s", resp.StatusCode, truncate(raw, 256))
+	}
+	var out signResponse
+	if err := json.Unmarshal(raw, &out); err != nil {
+		return Envelope{}, "", fmt.Errorf("decode sign response: %w", err)
+	}
+	if out.ContentHash == "" {
+		return Envelope{}, "", errors.New("signer: response missing content_hash")
+	}
+	return out.Envelope, out.ContentHash, nil
+}
+
+func truncate(b []byte, n int) string {
+	if len(b) <= n {
+		return string(b)
+	}
+	return string(b[:n]) + "…"
+}

services/approval-service/internal/signer/signer_test.go

@@ -0,0 +1,88 @@
+package signer
+
+import (
+	"context"
+	"encoding/json"
+	"errors"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+	"time"
+)
+
+func TestSignDSSE_HappyPath(t *testing.T) {
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		if r.URL.Path != "/api/v1/sign/dsse" {
+			t.Errorf("unexpected path %q", r.URL.Path)
+		}
+		if got := r.Header.Get("Authorization"); got != "Bearer tok" {
+			t.Errorf("auth header = %q", got)
+		}
+		var body signRequest
+		if err := json.NewDecoder(r.Body).Decode(&body); err != nil {
+			t.Fatalf("decode: %v", err)
+		}
+		if body.KeyRef != "key-x" {
+			t.Errorf("keyRef = %q", body.KeyRef)
+		}
+		resp := signResponse{
+			Envelope:    Envelope{PayloadType: "application/vnd.in-toto+json", Payload: "aGk"},
+			ContentHash: "sha256:deadbeef",
+			SignedAt:    time.Now(),
+		}
+		w.Header().Set("Content-Type", "application/json")
+		_ = json.NewEncoder(w).Encode(resp)
+	}))
+	defer srv.Close()
+
+	c := Client{BaseURL: srv.URL, TokenSource: StaticToken("tok")}
+	env, hash, err := c.SignDSSE(context.Background(), "key-x", Statement{"_type": "x"})
+	if err != nil {
+		t.Fatalf("SignDSSE: %v", err)
+	}
+	if hash != "sha256:deadbeef" {
+		t.Errorf("hash = %q", hash)
+	}
+	if env.PayloadType != "application/vnd.in-toto+json" {
+		t.Errorf("payloadType = %q", env.PayloadType)
+	}
+}
+
+func TestSignDSSE_5xxMapsToUnavailable(t *testing.T) {
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, _ *http.Request) {
+		http.Error(w, "boom", http.StatusInternalServerError)
+	}))
+	defer srv.Close()
+	c := Client{BaseURL: srv.URL}
+	_, _, err := c.SignDSSE(context.Background(), "k", Statement{"_type": "x"})
+	if !errors.Is(err, ErrSignerUnavailable) {
+		t.Fatalf("want ErrSignerUnavailable, got %v", err)
+	}
+}
+
+func TestSignDSSE_ConnRefusedMapsToUnavailable(t *testing.T) {
+	// Nonexistent address — the dial will fail immediately.
+	c := Client{
+		BaseURL:    "http://127.0.0.1:1", // reserved, almost always refused
+		HTTPClient: &http.Client{Timeout: 500 * time.Millisecond},
+	}
+	_, _, err := c.SignDSSE(context.Background(), "k", Statement{"_type": "x"})
+	if !errors.Is(err, ErrSignerUnavailable) {
+		t.Fatalf("want ErrSignerUnavailable, got %v", err)
+	}
+}
+
+func TestSignDSSE_4xxDoesNotLookUnavailable(t *testing.T) {
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, _ *http.Request) {
+		w.WriteHeader(http.StatusForbidden)
+	}))
+	defer srv.Close()
+	c := Client{BaseURL: srv.URL}
+	_, _, err := c.SignDSSE(context.Background(), "k", Statement{"_type": "x"})
+	if err == nil {
+		t.Fatalf("expected error")
+	}
+	if errors.Is(err, ErrSignerUnavailable) {
+		t.Fatalf("4xx must not be reported as ErrSignerUnavailable: %v", err)
+	}
+}

services/approval-service/internal/store/memory.go

@@ -0,0 +1,136 @@
+package store
+
+import (
+	"context"
+	"sync"
+	"time"
+)
+
+// Memory is the Phase-1 in-process Store. Thread-safe via a single RWMutex;
+// each call is cheap enough that per-table locks would be over-engineering.
+type Memory struct {
+	mu        sync.RWMutex
+	sessions  map[string]Session
+	previews  map[string]Preview
+	approvals map[string]Approval
+}
+
+// NewMemory returns an empty Memory store.
+func NewMemory() *Memory {
+	return &Memory{
+		sessions:  map[string]Session{},
+		previews:  map[string]Preview{},
+		approvals: map[string]Approval{},
+	}
+}
+
+func (m *Memory) CreateSession(_ context.Context, s Session) error {
+	m.mu.Lock()
+	defer m.mu.Unlock()
+	m.sessions[s.ID] = s
+	return nil
+}
+
+func (m *Memory) GetSession(_ context.Context, id string) (Session, error) {
+	m.mu.RLock()
+	defer m.mu.RUnlock()
+	s, ok := m.sessions[id]
+	if !ok {
+		return Session{}, ErrNotFound
+	}
+	return s, nil
+}
+
+func (m *Memory) SavePreview(_ context.Context, p Preview) error {
+	m.mu.Lock()
+	defer m.mu.Unlock()
+	m.previews[p.ID] = p
+	return nil
+}
+
+func (m *Memory) GetPreview(_ context.Context, id string) (Preview, error) {
+	m.mu.RLock()
+	defer m.mu.RUnlock()
+	p, ok := m.previews[id]
+	if !ok {
+		return Preview{}, ErrNotFound
+	}
+	// Return a copy so callers cannot mutate our byte slices.
+	return clonePreview(p), nil
+}
+
+// ConsumePreview marks the preview as consumed if it is still valid and
+// unconsumed. The returned Preview is the pre-mutation copy.
+func (m *Memory) ConsumePreview(_ context.Context, id string, now time.Time) (Preview, error) {
+	m.mu.Lock()
+	defer m.mu.Unlock()
+	p, ok := m.previews[id]
+	if !ok {
+		return Preview{}, ErrNotFound
+	}
+	if p.ConsumedAt != nil {
+		return Preview{}, ErrAlreadyConsumed
+	}
+	snapshot := clonePreview(p)
+	ts := now
+	p.ConsumedAt = &ts
+	m.previews[id] = p
+	return snapshot, nil
+}
+
+func (m *Memory) SaveApproval(_ context.Context, a Approval) error {
+	m.mu.Lock()
+	defer m.mu.Unlock()
+	m.approvals[a.ID] = a
+	return nil
+}
+
+func (m *Memory) MarkApprovalLogged(_ context.Context, id string, logIndex int64, loggedAt time.Time) error {
+	m.mu.Lock()
+	defer m.mu.Unlock()
+	a, ok := m.approvals[id]
+	if !ok {
+		return ErrNotFound
+	}
+	a.TLogStatus = TLogLogged
+	a.LogIndex = &logIndex
+	a.LoggedAt = &loggedAt
+	a.TLogError = ""
+	m.approvals[id] = a
+	return nil
+}
+
+func (m *Memory) MarkApprovalTLogError(_ context.Context, id string, errorMsg string) error {
+	m.mu.Lock()
+	defer m.mu.Unlock()
+	a, ok := m.approvals[id]
+	if !ok {
+		return ErrNotFound
+	}
+	// Keep status at attestation-pending — a reconciler will retry. We
+	// only record the last error message for diagnostics.
+	a.TLogError = errorMsg
+	m.approvals[id] = a
+	return nil
+}
+
+// GetApproval is a test-side accessor; not part of the Store interface
+// because the HTTP handlers never need it.
+func (m *Memory) GetApproval(id string) (Approval, bool) {
+	m.mu.RLock()
+	defer m.mu.RUnlock()
+	a, ok := m.approvals[id]
+	return a, ok
+}
+
+func clonePreview(p Preview) Preview {
+	out := p
+	out.ContentCanonical = append([]byte(nil), p.ContentCanonical...)
+	out.Salt = append([]byte(nil), p.Salt...)
+	out.Nonce = append([]byte(nil), p.Nonce...)
+	if p.ConsumedAt != nil {
+		t := *p.ConsumedAt
+		out.ConsumedAt = &t
+	}
+	return out
+}

services/approval-service/internal/store/postgres.go

@@ -0,0 +1,41 @@
+package store
+
+import (
+	"context"
+	"errors"
+	"time"
+)
+
+// Postgres is the production Store. **Skeleton** mirroring the pattern used
+// by services/admin-api/internal/store/postgres.go: every method returns
+// errPGUnimplemented until the pgxpool wiring lands. The schema is
+// authoritative in db/trust/migrations/0004_approval_sessions.*.sql.
+type Postgres struct {
+	// pool *pgxpool.Pool // kept out of go.mod in the skeleton
+}
+
+var errPGUnimplemented = errors.New("postgres store is a skeleton; use NewMemory for Phase 1")
+
+// NewPostgres returns a zero-value Postgres. Real wiring is Phase 2.
+func NewPostgres( /* conn string, logger */ ) (*Postgres, error) {
+	return &Postgres{}, nil
+}
+
+func (p *Postgres) CreateSession(_ context.Context, _ Session) error { return errPGUnimplemented }
+func (p *Postgres) GetSession(_ context.Context, _ string) (Session, error) {
+	return Session{}, errPGUnimplemented
+}
+func (p *Postgres) SavePreview(_ context.Context, _ Preview) error { return errPGUnimplemented }
+func (p *Postgres) GetPreview(_ context.Context, _ string) (Preview, error) {
+	return Preview{}, errPGUnimplemented
+}
+func (p *Postgres) ConsumePreview(_ context.Context, _ string, _ time.Time) (Preview, error) {
+	return Preview{}, errPGUnimplemented
+}
+func (p *Postgres) SaveApproval(_ context.Context, _ Approval) error { return errPGUnimplemented }
+func (p *Postgres) MarkApprovalLogged(_ context.Context, _ string, _ int64, _ time.Time) error {
+	return errPGUnimplemented
+}
+func (p *Postgres) MarkApprovalTLogError(_ context.Context, _ string, _ string) error {
+	return errPGUnimplemented
+}

services/approval-service/internal/store/store.go

@@ -0,0 +1,90 @@
+// Package store defines the persistence contract for approval_sessions,
+// approval_previews, and approvals. Phase 1 ships an in-memory impl; the
+// Postgres schema is in db/trust/migrations/0004_approval_sessions.*.sql
+// and wired via a skeleton Postgres type (see postgres.go) so the HTTP
+// layer stays unchanged when the real pgxpool wiring lands.
+package store
+
+import (
+	"context"
+	"errors"
+	"time"
+
+	"basicstack.de/proofedmesh/services/approval-service/internal/signer"
+)
+
+// ErrNotFound is returned by lookup methods when the row does not exist
+// or has expired.
+var ErrNotFound = errors.New("store: not found")
+
+// ErrAlreadyConsumed is returned by ConsumePreview when the preview has
+// already been consumed — the confirm endpoint MUST reject a replay.
+var ErrAlreadyConsumed = errors.New("store: preview already consumed")
+
+// Session is a per-browser-login approval session. active_until bounds
+// how long previews may be created against it.
+type Session struct {
+	ID          string
+	UserSub     string
+	ActiveUntil time.Time
+	CreatedAt   time.Time
+}
+
+// Preview is a server-rendered approval payload that has not yet been
+// confirmed. ContentCanonical lets the confirm endpoint recompute
+// H_content deterministically from the stored row.
+type Preview struct {
+	ID                 string
+	SessionID          string
+	UserSub            string
+	ContentHash        string
+	ContentCanonical   []byte
+	Salt               []byte
+	Nonce              []byte
+	VerificationDigits string
+	ExpiresAt          time.Time
+	CreatedAt          time.Time
+	ConsumedAt         *time.Time
+}
+
+// TLogStatus is the three-valued state of the Transparency-Log submit.
+type TLogStatus string
+
+const (
+	TLogPending TLogStatus = "attestation-pending"
+	TLogLogged  TLogStatus = "logged"
+	TLogFailed  TLogStatus = "failed"
+)
+
+// Approval is the confirmed, DSSE-signed approval record. If TLogStatus
+// is TLogPending/TLogFailed, log_index is nil and the attest-reconciler
+// (or a future worker) will replay the Transparency-Log submit against
+// the server's idempotent /api/v1/log/entries contract.
+type Approval struct {
+	ID             string
+	PreviewID      string
+	SessionID      string
+	UserSub        string
+	ContentHash    string
+	Envelope       signer.Envelope
+	AttestationRef string
+	TLogStatus     TLogStatus
+	LogIndex       *int64
+	TLogError      string
+	ConfirmedAt    time.Time
+	LoggedAt       *time.Time
+}
+
+// Store is the full persistence surface the HTTP service depends on.
+type Store interface {
+	CreateSession(ctx context.Context, s Session) error
+	GetSession(ctx context.Context, id string) (Session, error)
+
+	SavePreview(ctx context.Context, p Preview) error
+	GetPreview(ctx context.Context, id string) (Preview, error)
+	ConsumePreview(ctx context.Context, id string, now time.Time) (Preview, error)
+
+	SaveApproval(ctx context.Context, a Approval) error
+	MarkApprovalLogged(ctx context.Context, id string, logIndex int64, loggedAt time.Time) error
+	MarkApprovalTLogError(ctx context.Context, id string, errorMsg string) error
+}

services/approval-service/internal/tlog/submitter.go

@@ -0,0 +1,122 @@
+// Package tlog calls the transparency-log's POST /api/v1/log/entries
+// endpoint. Idempotent on the server side: resubmitting the same
+// (envelope, content_hash) returns the same log_index + inclusion proof.
+// See DEV-600 and services/transparency-log for the server-side contract.
+package tlog
+
+import (
+	"bytes"
+	"context"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"io"
+	"net/http"
+	"net/url"
+	"time"
+
+	"basicstack.de/proofedmesh/services/approval-service/internal/signer"
+)
+
+// InclusionProof mirrors the server-side ADR-0005 inclusion proof.
+type InclusionProof struct {
+	TreeSize          int64    `json:"tree_size"`
+	TreeRootHash      string   `json:"tree_root_hash"`
+	SignedTreeHeadRef string   `json:"signed_tree_head_ref"`
+	Hashes            []string `json:"hashes"`
+}
+
+// Receipt is what the transparency-log hands back on a successful submit.
+type Receipt struct {
+	LogIndex       int64          `json:"log_index"`
+	ContentHash    string         `json:"content_hash"`
+	LoggedAt       time.Time      `json:"logged_at"`
+	InclusionProof InclusionProof `json:"inclusion_proof"`
+}
+
+// ErrTLogUnavailable classifies connection errors and 5xx responses from
+// the transparency-log. Callers (the HTTP /confirm handler) use this to
+// decide between returning a logged approval and an attestation-pending
+// one — the Approval row is persisted either way.
+var ErrTLogUnavailable = errors.New("tlog: transparency-log unavailable")
+
+// Client is the tlog submit client.
+type Client struct {
+	BaseURL     string
+	HTTPClient  *http.Client
+	TokenSource signer.TokenSource
+}
+
+type submitRequest struct {
+	Envelope    signer.Envelope `json:"envelope"`
+	ContentHash string          `json:"content_hash"`
+}
+
+// Submit sends env + its contentHash to the transparency-log. Returns the
+// server receipt on 200/201 (idempotent repeat / fresh insert) and
+// ErrTLogUnavailable on any transport-level or 5xx failure. All other
+// non-2xx responses are reported with the raw status.
+func (c Client) Submit(ctx context.Context, env signer.Envelope, contentHash string) (Receipt, error) {
+	if c.BaseURL == "" {
+		return Receipt{}, errors.New("tlog.Client: BaseURL is empty")
+	}
+	hc := c.HTTPClient
+	if hc == nil {
+		hc = &http.Client{Timeout: 10 * time.Second}
+	}
+	body, err := json.Marshal(submitRequest{Envelope: env, ContentHash: contentHash})
+	if err != nil {
+		return Receipt{}, fmt.Errorf("marshal submit: %w", err)
+	}
+	endpoint, err := url.JoinPath(c.BaseURL, "/api/v1/log/entries")
+	if err != nil {
+		return Receipt{}, fmt.Errorf("join tlog url: %w", err)
+	}
+	req, err := http.NewRequestWithContext(ctx, http.MethodPost, endpoint, bytes.NewReader(body))
+	if err != nil {
+		return Receipt{}, err
+	}
+	req.Header.Set("Content-Type", "application/json")
+	req.Header.Set("Accept", "application/json")
+	if c.TokenSource != nil {
+		tok, err := c.TokenSource.Token(ctx)
+		if err != nil {
+			return Receipt{}, fmt.Errorf("token: %w", err)
+		}
+		if tok != "" {
+			req.Header.Set("Authorization", "Bearer "+tok)
+		}
+	}
+	resp, err := hc.Do(req)
+	if err != nil {
+		return Receipt{}, fmt.Errorf("%w: %v", ErrTLogUnavailable, err)
+	}
+	defer resp.Body.Close()
+	raw, _ := io.ReadAll(io.LimitReader(resp.Body, 1<<20))
+	switch {
+	case resp.StatusCode == http.StatusOK, resp.StatusCode == http.StatusCreated:
+		// ok
+	case resp.StatusCode >= 500:
+		return Receipt{}, fmt.Errorf("%w: status %d: %s", ErrTLogUnavailable, resp.StatusCode, truncate(raw, 256))
+	default:
+		return Receipt{}, fmt.Errorf("tlog: status %d: %s", resp.StatusCode, truncate(raw, 256))
+	}
+	var out Receipt
+	if err := json.Unmarshal(raw, &out); err != nil {
+		return Receipt{}, fmt.Errorf("decode receipt: %w", err)
+	}
+	if out.ContentHash != contentHash {
+		return out, fmt.Errorf("tlog returned content_hash %q != sent %q", out.ContentHash, contentHash)
+	}
+	if out.LogIndex < 0 {
+		return out, fmt.Errorf("tlog returned negative log_index %d", out.LogIndex)
+	}
+	return out, nil
+}
+
+func truncate(b []byte, n int) string {
+	if len(b) <= n {
+		return string(b)
+	}
+	return string(b[:n]) + "…"
+}

services/approval-service/internal/webauthn/webauthn.go

@@ -0,0 +1,225 @@
+// Package webauthn is the approval-service's Phase-1 WebAuthn verifier.
+//
+// It is NOT the full go-webauthn/webauthn library — Phase 1 only needs to
+// verify assertions against mock credentials registered in-memory for the
+// test agent. The data types on the wire (`client_data_json`,
+// `authenticator_data`, `signature`, `credential_id`) stay WebAuthn
+// compatible so a Phase-2 swap to github.com/go-webauthn/webauthn is a
+// pure dependency change, not an API break for the browser.
+//
+// Threat model this implementation addresses:
+//
+//   - The challenge the browser signs is bound to H_content via
+//     content.ChallengeFor (nonce || sha256(canonical content)). An
+//     attacker rewriting the preview payload after the human saw it would
+//     have to find a hash collision, so we check the stored challenge
+//     bytes-for-bytes.
+//   - The authenticator type field (`type` in clientDataJSON) MUST be
+//     "webauthn.get", so a reused registration ceremony signature is
+//     rejected.
+//   - The RP ID hash in authenticator_data MUST match our configured RP;
+//     otherwise an assertion scoped to a different origin would be accepted.
+//
+// What this implementation deliberately does NOT do:
+//
+//   - It does not enforce user verification flags (UV bit). Phase 2 will.
+//   - It does not implement the WebAuthn attestation path (registration);
+//     credentials are inserted directly via Store.AddCredential.
+//   - It only knows about Ed25519 public keys — all our mock credentials
+//     use Ed25519. ES256/RS256 land with the library swap in Phase 2.
+package webauthn
+
+import (
+	"crypto/ed25519"
+	"crypto/sha256"
+	"crypto/subtle"
+	"encoding/base64"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"strings"
+	"sync"
+)
+
+// Assertion mirrors the WebAuthn PublicKeyCredential assertion response
+// (base64url-encoded fields; raw bytes are decoded by Verify).
+type Assertion struct {
+	CredentialID      string `json:"credential_id"`
+	ClientDataJSON    string `json:"client_data_json"`
+	AuthenticatorData string `json:"authenticator_data"`
+	Signature         string `json:"signature"`
+}
+
+// Credential is a registered WebAuthn credential bound to a user sub.
+type Credential struct {
+	ID        string              // base64url, matches assertion.credential_id
+	UserSub   string              // Pocket-ID subject
+	PublicKey ed25519.PublicKey   // Phase 1: only Ed25519.
+}
+
+// Store is the in-memory credential registry.
+type Store struct {
+	mu    sync.RWMutex
+	creds map[string]Credential // key = CredentialID
+}
+
+// NewStore constructs an empty in-memory credential store.
+func NewStore() *Store {
+	return &Store{creds: map[string]Credential{}}
+}
+
+// AddCredential registers c. Used by test agents and the Phase-2 passkey
+// enrollment flow.
+func (s *Store) AddCredential(c Credential) error {
+	if c.ID == "" {
+		return errors.New("webauthn: credential ID is empty")
+	}
+	if c.UserSub == "" {
+		return errors.New("webauthn: credential has no user sub")
+	}
+	if len(c.PublicKey) != ed25519.PublicKeySize {
+		return errors.New("webauthn: credential public key must be Ed25519 (32 bytes)")
+	}
+	s.mu.Lock()
+	defer s.mu.Unlock()
+	s.creds[c.ID] = c
+	return nil
+}
+
+// Get returns the credential registered under id.
+func (s *Store) Get(id string) (Credential, bool) {
+	s.mu.RLock()
+	defer s.mu.RUnlock()
+	c, ok := s.creds[id]
+	return c, ok
+}
+
+// VerifyConfig configures Verify's RP and origin checks.
+type VerifyConfig struct {
+	// RPID is the hostname the authenticator scoped the credential to.
+	// authenticator_data starts with sha256(RPID).
+	RPID string
+	// AllowedOrigins is the exact set of accepted browser origins (e.g.
+	// "https://trust.basicstack.de"). The assertion's clientDataJSON
+	// `origin` MUST be one of these.
+	AllowedOrigins []string
+}
+
+// ErrChallengeMismatch means the challenge in clientDataJSON did not match
+// what the preview endpoint stored — i.e. H_content was tampered with.
+var ErrChallengeMismatch = errors.New("webauthn: challenge in clientDataJSON does not match stored challenge")
+
+// ErrCredentialUnknown means the asserted credential is not registered.
+var ErrCredentialUnknown = errors.New("webauthn: credential not registered")
+
+// ErrAssertionInvalid is returned for any lower-level verification failure
+// (bad origin, wrong type, bad signature). The caller maps this to HTTP
+// 401 to avoid leaking which specific check failed to a probing attacker.
+var ErrAssertionInvalid = errors.New("webauthn: assertion invalid")
+
+// Verify checks a WebAuthn assertion against (a) the expected challenge
+// bytes and (b) a registered credential. On success it returns the
+// matched credential.
+func Verify(cfg VerifyConfig, store *Store, a Assertion, expectedChallenge []byte) (Credential, error) {
+	if store == nil {
+		return Credential{}, errors.New("webauthn: store is nil")
+	}
+	if cfg.RPID == "" {
+		return Credential{}, errors.New("webauthn: RPID is empty")
+	}
+	if len(cfg.AllowedOrigins) == 0 {
+		return Credential{}, errors.New("webauthn: no allowed origins configured")
+	}
+
+	cred, ok := store.Get(a.CredentialID)
+	if !ok {
+		return Credential{}, ErrCredentialUnknown
+	}
+
+	cdJSON, err := base64.RawURLEncoding.DecodeString(stripB64Pad(a.ClientDataJSON))
+	if err != nil {
+		return cred, fmt.Errorf("%w: client_data_json b64: %v", ErrAssertionInvalid, err)
+	}
+	authData, err := base64.RawURLEncoding.DecodeString(stripB64Pad(a.AuthenticatorData))
+	if err != nil {
+		return cred, fmt.Errorf("%w: authenticator_data b64: %v", ErrAssertionInvalid, err)
+	}
+	sig, err := base64.RawURLEncoding.DecodeString(stripB64Pad(a.Signature))
+	if err != nil {
+		return cred, fmt.Errorf("%w: signature b64: %v", ErrAssertionInvalid, err)
+	}
+
+	var cd clientData
+	if err := json.Unmarshal(cdJSON, &cd); err != nil {
+		return cred, fmt.Errorf("%w: client_data decode: %v", ErrAssertionInvalid, err)
+	}
+	if cd.Type != "webauthn.get" {
+		return cred, fmt.Errorf("%w: type %q", ErrAssertionInvalid, cd.Type)
+	}
+	if !originAllowed(cfg.AllowedOrigins, cd.Origin) {
+		return cred, fmt.Errorf("%w: origin %q not allowed", ErrAssertionInvalid, cd.Origin)
+	}
+
+	gotChal, err := base64.RawURLEncoding.DecodeString(stripB64Pad(cd.Challenge))
+	if err != nil {
+		return cred, fmt.Errorf("%w: challenge b64: %v", ErrAssertionInvalid, err)
+	}
+	if subtle.ConstantTimeCompare(gotChal, expectedChallenge) != 1 {
+		return cred, ErrChallengeMismatch
+	}
+
+	// authenticator_data layout per the WebAuthn spec:
+	//   rpIdHash (32) || flags (1) || signCount (4) || <attested cred data>?
+	if len(authData) < 37 {
+		return cred, fmt.Errorf("%w: authenticator_data too short", ErrAssertionInvalid)
+	}
+	rpHash := sha256.Sum256([]byte(cfg.RPID))
+	if subtle.ConstantTimeCompare(authData[:32], rpHash[:]) != 1 {
+		return cred, fmt.Errorf("%w: rpIdHash mismatch", ErrAssertionInvalid)
+	}
+
+	// Signed-over bytes per the spec: authenticator_data || sha256(clientDataJSON).
+	cdHash := sha256.Sum256(cdJSON)
+	signed := make([]byte, 0, len(authData)+len(cdHash))
+	signed = append(signed, authData...)
+	signed = append(signed, cdHash[:]...)
+
+	if !ed25519.Verify(cred.PublicKey, signed, sig) {
+		return cred, fmt.Errorf("%w: ed25519 signature verification failed", ErrAssertionInvalid)
+	}
+	return cred, nil
+}
+
+// clientData is the subset of CollectedClientData we care about.
+type clientData struct {
+	Type      string `json:"type"`
+	Challenge string `json:"challenge"`
+	Origin    string `json:"origin"`
+}
+
+func originAllowed(allowed []string, got string) bool {
+	for _, o := range allowed {
+		if strings.EqualFold(o, got) {
+			return true
+		}
+	}
+	return false
+}
+
+// stripB64Pad lets us accept both padded (`...==`) and unpadded base64url
+// since different browsers emit different forms.
+func stripB64Pad(s string) string {
+	return strings.TrimRight(s, "=")
+}
+
+// MakeAuthenticatorData is a test helper: builds a minimal
+// authenticator_data (rpIdHash || flags=0x01 || signCount=0) for the
+// given RP ID. Production enrollment never comes through this path.
+func MakeAuthenticatorData(rpID string) []byte {
+	sum := sha256.Sum256([]byte(rpID))
+	buf := make([]byte, 32+1+4)
+	copy(buf, sum[:])
+	buf[32] = 0x01 // UP (user present); UV left zero for the Phase-1 shim.
+	// sign count stays zero
+	return buf
+}

services/approval-service/internal/webauthn/webauthn_test.go

@@ -0,0 +1,134 @@
+package webauthn
+
+import (
+	"crypto/ed25519"
+	"crypto/rand"
+	"crypto/sha256"
+	"encoding/base64"
+	"encoding/json"
+	"errors"
+	"testing"
+)
+
+func TestVerify_HappyPath(t *testing.T) {
+	pub, priv, cred, store := setupCredential(t, "alice")
+	_ = pub
+	challenge := []byte("challenge-bytes-just-for-the-test")
+	a := makeAssertion(t, priv, cred.ID, "trust.basicstack.de", "https://trust.basicstack.de", challenge)
+
+	cfg := VerifyConfig{RPID: "trust.basicstack.de", AllowedOrigins: []string{"https://trust.basicstack.de"}}
+	got, err := Verify(cfg, store, a, challenge)
+	if err != nil {
+		t.Fatalf("Verify: %v", err)
+	}
+	if got.ID != cred.ID {
+		t.Errorf("credential id mismatch")
+	}
+}
+
+func TestVerify_WrongChallenge(t *testing.T) {
+	_, priv, cred, store := setupCredential(t, "alice")
+	challenge := []byte("original-challenge-bytes-xxxxxxxx")
+	a := makeAssertion(t, priv, cred.ID, "trust.basicstack.de", "https://trust.basicstack.de", challenge)
+
+	cfg := VerifyConfig{RPID: "trust.basicstack.de", AllowedOrigins: []string{"https://trust.basicstack.de"}}
+	_, err := Verify(cfg, store, a, []byte("different-challenge-bytes-yyyyyy"))
+	if !errors.Is(err, ErrChallengeMismatch) {
+		t.Fatalf("want ErrChallengeMismatch, got %v", err)
+	}
+}
+
+func TestVerify_UnknownCredential(t *testing.T) {
+	store := NewStore()
+	cfg := VerifyConfig{RPID: "trust.basicstack.de", AllowedOrigins: []string{"https://trust.basicstack.de"}}
+	_, err := Verify(cfg, store, Assertion{CredentialID: "nope"}, []byte("c"))
+	if !errors.Is(err, ErrCredentialUnknown) {
+		t.Fatalf("want ErrCredentialUnknown, got %v", err)
+	}
+}
+
+func TestVerify_WrongOrigin(t *testing.T) {
+	_, priv, cred, store := setupCredential(t, "alice")
+	challenge := []byte("challenge-xxx-xxx-xxx-xxx")
+	a := makeAssertion(t, priv, cred.ID, "trust.basicstack.de", "https://evil.example", challenge)
+	cfg := VerifyConfig{RPID: "trust.basicstack.de", AllowedOrigins: []string{"https://trust.basicstack.de"}}
+	_, err := Verify(cfg, store, a, challenge)
+	if err == nil || !errors.Is(err, ErrAssertionInvalid) {
+		t.Fatalf("want ErrAssertionInvalid, got %v", err)
+	}
+}
+
+func TestVerify_WrongType(t *testing.T) {
+	_, priv, cred, store := setupCredential(t, "alice")
+	challenge := []byte("challenge-xxx-xxx-xxx-xxx")
+	a := makeAssertionWithType(t, priv, cred.ID, "trust.basicstack.de", "https://trust.basicstack.de", challenge, "webauthn.create")
+	cfg := VerifyConfig{RPID: "trust.basicstack.de", AllowedOrigins: []string{"https://trust.basicstack.de"}}
+	_, err := Verify(cfg, store, a, challenge)
+	if !errors.Is(err, ErrAssertionInvalid) {
+		t.Fatalf("want ErrAssertionInvalid, got %v", err)
+	}
+}
+
+func TestVerify_BadSignature(t *testing.T) {
+	_, priv, cred, store := setupCredential(t, "alice")
+	challenge := []byte("challenge-xxx-xxx-xxx-xxx")
+	a := makeAssertion(t, priv, cred.ID, "trust.basicstack.de", "https://trust.basicstack.de", challenge)
+	// Tamper with the signature.
+	sig, _ := base64.RawURLEncoding.DecodeString(a.Signature)
+	sig[0] ^= 0xff
+	a.Signature = base64.RawURLEncoding.EncodeToString(sig)
+
+	cfg := VerifyConfig{RPID: "trust.basicstack.de", AllowedOrigins: []string{"https://trust.basicstack.de"}}
+	_, err := Verify(cfg, store, a, challenge)
+	if !errors.Is(err, ErrAssertionInvalid) {
+		t.Fatalf("want ErrAssertionInvalid, got %v", err)
+	}
+}
+
+// --- helpers --------------------------------------------------------------
+
+func setupCredential(t *testing.T, userSub string) (ed25519.PublicKey, ed25519.PrivateKey, Credential, *Store) {
+	t.Helper()
+	pub, priv, err := ed25519.GenerateKey(rand.Reader)
+	if err != nil {
+		t.Fatalf("gen key: %v", err)
+	}
+	idBytes := make([]byte, 16)
+	_, _ = rand.Read(idBytes)
+	cred := Credential{
+		ID:        base64.RawURLEncoding.EncodeToString(idBytes),
+		UserSub:   userSub,
+		PublicKey: pub,
+	}
+	store := NewStore()
+	if err := store.AddCredential(cred); err != nil {
+		t.Fatalf("AddCredential: %v", err)
+	}
+	return pub, priv, cred, store
+}
+
+// makeAssertion signs a mock WebAuthn assertion with the given private
+// key over the standard authenticator_data || sha256(clientDataJSON).
+func makeAssertion(t *testing.T, priv ed25519.PrivateKey, credID, rpID, origin string, challenge []byte) Assertion {
+	return makeAssertionWithType(t, priv, credID, rpID, origin, challenge, "webauthn.get")
+}
+
+func makeAssertionWithType(t *testing.T, priv ed25519.PrivateKey, credID, rpID, origin string, challenge []byte, typ string) Assertion {
+	t.Helper()
+	cd := map[string]string{
+		"type":      typ,
+		"challenge": base64.RawURLEncoding.EncodeToString(challenge),
+		"origin":    origin,
+	}
+	cdBytes, _ := json.Marshal(cd)
+	authData := MakeAuthenticatorData(rpID)
+	cdHash := sha256.Sum256(cdBytes)
+	signed := append(append([]byte(nil), authData...), cdHash[:]...)
+	sig := ed25519.Sign(priv, signed)
+	return Assertion{
+		CredentialID:      credID,
+		ClientDataJSON:    base64.RawURLEncoding.EncodeToString(cdBytes),
+		AuthenticatorData: base64.RawURLEncoding.EncodeToString(authData),
+		Signature:         base64.RawURLEncoding.EncodeToString(sig),
+	}
+}

services/approval-service/pkg/httpapi/types.go

@@ -0,0 +1,65 @@
+// Package httpapi exposes the stable wire types of the approval-service.
+// Clients (admin UIs, CLI integrations, Phase-2 webauthn library adapters)
+// import this package; the internal/httpapi handlers reuse these same
+// structs so the on-wire shape matches the exported contract.
+package httpapi
+
+import "time"
+
+// CreateSessionResponse is returned by POST /api/v1/sessions.
+type CreateSessionResponse struct {
+	SessionID   string    `json:"session_id"`
+	UserSub     string    `json:"user_sub"`
+	ActiveUntil time.Time `json:"active_until"`
+}
+
+// PreviewRequest is the body of POST /api/v1/approvals/preview.
+type PreviewRequest struct {
+	SessionID string         `json:"session_id"`
+	Content   map[string]any `json:"content"`
+}
+
+// PreviewResponse is returned by POST /api/v1/approvals/preview.
+type PreviewResponse struct {
+	PreviewID          string    `json:"preview_id"`
+	ContentHash        string    `json:"content_hash"`
+	VerificationDigits string    `json:"verification_digits"`
+	WebauthnChallenge  string    `json:"webauthn_challenge"`
+	ExpiresAt          time.Time `json:"expires_at"`
+}
+
+// Assertion mirrors the WebAuthn PublicKeyCredentialAssertionResponse.
+// All fields are base64url-encoded.
+type Assertion struct {
+	CredentialID      string `json:"credential_id"`
+	ClientDataJSON    string `json:"client_data_json"`
+	AuthenticatorData string `json:"authenticator_data"`
+	Signature         string `json:"signature"`
+}
+
+// ConfirmRequest is the body of POST /api/v1/approvals/confirm.
+type ConfirmRequest struct {
+	PreviewID string    `json:"preview_id"`
+	Assertion Assertion `json:"assertion"`
+}
+
+// ConfirmResponse is returned by POST /api/v1/approvals/confirm. LogIndex
+// is nil (and TLogStatus is "attestation-pending") when the TLog submit
+// failed; the Approval row is persisted either way.
+type ConfirmResponse struct {
+	ApprovalID     string `json:"approval_id"`
+	AttestationRef string `json:"attestation_ref"`
+	LogIndex       *int64 `json:"log_index"`
+	TLogStatus     string `json:"tlog_status"`
+}
+
+// Error is the stable error envelope.
+type Error struct {
+	Error ErrorBody `json:"error"`
+}
+
+// ErrorBody is the inner typed error.
+type ErrorBody struct {
+	Code    string `json:"code"`
+	Message string `json:"message"`
+}

services/signing-service/Dockerfile

@@ -9,17 +9,21 @@ ENV CGO_ENABLED=0 \
 
 WORKDIR /src
 
-# Only the signing-service module is needed. Copy the module files first so
-# the dependency download layer is cacheable independently of source edits.
-COPY services/signing-service/go.mod ./
-# go.sum will be copied in when the module gains external deps; today the
-# module is stdlib-only.
+# The image reproduces the repo layout under /src so Go module paths and
+# the OPA policy's relative location (`../../../../policies/sinks/...`
+# in tests) line up both in CI and inside the image.
+COPY services/signing-service/go.mod services/signing-service/go.sum ./services/signing-service/
 RUN --mount=type=cache,target=/root/.cache/go-build \
     --mount=type=cache,target=/go/pkg/mod \
-    go mod download || true
+    cd services/signing-service && go mod download
 
-COPY services/signing-service/ ./
+COPY services/signing-service/ ./services/signing-service/
+# The OPA Rego policy ships with the image for dev / smoke runs. GitOps
+# mounts it from a ConfigMap at /etc/signing-service/policies at runtime
+# and wins over the baked-in copy.
+COPY policies/sinks/signing_service.rego ./policies/sinks/signing_service.rego
 
+WORKDIR /src/services/signing-service
 RUN --mount=type=cache,target=/root/.cache/go-build \
     --mount=type=cache,target=/go/pkg/mod \
     go vet ./... && \

services/signing-service/cmd/signing-service/main.go

@@ -1,9 +1,13 @@
 // Command signing-service exposes POST /api/v1/sign/dsse per ADR-0005.
 //
-// Dev mode is self-contained: in-memory Ed25519 keyring, AllowAll policy,
-// static bearer-to-subject table. Prod wiring (OpenBao Transit, OPA, Pocket
-// ID JWKS) is in follow-up subtasks; the interfaces are already in place so
-// swapping backends does not touch the HTTP layer.
+// Modes
+//
+//   - Dev (default): memory signer, AllowAll policy, static bearer table.
+//     Still used by CI and local integration tests.
+//   - Prod: Pocket-ID JWKS validator, K8s TokenReview-backed workload
+//     identity, trust-api Postgres agent registry, OPA Rego policy. Any
+//     combination of the four may be enabled via flags; main.go flips the
+//     Server composition accordingly.
 package main
 
 import (
@@ -23,6 +27,7 @@ import (
 
 	"basicstack.de/proofedmesh/services/signing-service/internal/httpapi"
 	"basicstack.de/proofedmesh/services/signing-service/internal/policy"
+	"basicstack.de/proofedmesh/services/signing-service/internal/registry"
 	"basicstack.de/proofedmesh/services/signing-service/internal/signer"
 	"basicstack.de/proofedmesh/services/signing-service/internal/token"
 )
@@ -35,8 +40,21 @@ func main() {
 	keysFromEnv := flag.Bool("keys-from-env", false,
 		"when true (memory backend), read KEY_<slug>=<hex> env for each key_ref instead of generating")
 	bearers := flag.String("bearers", "dev-token=agent-admin-api",
-		"comma-separated bearer=subject pairs for the static token validator")
+		"comma-separated bearer=subject pairs for the static token validator (ignored when -pocket-id-issuer is set)")
 	genDevKeyAndExit := flag.Bool("gen-dev-key", false, "generate one dev Ed25519 key and exit (prints hex)")
+
+	// Prod wiring flags (DEV-609):
+	pocketIDIssuer := flag.String("pocket-id-issuer", "",
+		"Pocket-ID issuer URL for OIDC discovery; when set, the Pocket-ID JWKS validator replaces the static bearer table")
+	pocketIDAudience := flag.String("pocket-id-audience", "",
+		"expected `aud` claim on Pocket-ID tokens; empty disables aud check")
+	k8sTokenReview := flag.String("k8s-tokenreview", "off",
+		"on|off: when on, require X-Workload-Token and perform TokenReview against the Kubernetes API server (via in-cluster SA credentials)")
+	registryDSN := flag.String("registry-dsn", "",
+		"Postgres DSN for the trust-api agent registry (e.g. postgres://signing-service:...@trust-pg.agent-trust/trust?sslmode=verify-full); empty disables the structured policy path")
+	policyBundle := flag.String("policy-bundle", "",
+		"path to the OPA Rego policy file for the signing-service (e.g. /etc/signing-service/policies/signing_service.rego); empty disables the structured policy path")
+
 	flag.Parse()
 
 	logger := slog.New(slog.NewJSONHandler(os.Stdout, nil))
@@ -51,52 +69,75 @@ func main() {
 		return
 	}
 
-	var sgn signer.Signer
-	switch *backend {
-	case "memory":
-		mem := signer.NewInMemory()
-		for _, kr := range splitCSV(*keyRefs) {
-			var priv ed25519.PrivateKey
-			if *keysFromEnv {
-				envName := envNameForKey(kr)
-				raw := os.Getenv(envName)
-				if raw == "" {
-					logger.Error("missing env for key", "env", envName)
-					os.Exit(1)
-				}
-				p, err := signer.DecodeHexEd25519Key(raw)
-				if err != nil {
-					logger.Error("bad env key", "env", envName, "err", err)
-					os.Exit(1)
-				}
-				priv = p
-			} else {
-				_, p, err := ed25519.GenerateKey(rand.Reader)
-				if err != nil {
-					logger.Error("gen key", "err", err)
-					os.Exit(1)
-				}
-				priv = p
-				logger.Warn("generated ephemeral dev key — not safe for prod", "key_ref", kr)
-			}
-			mem.AddKey(kr, priv)
-		}
-		sgn = mem
-	case "openbao":
-		logger.Error("openbao backend not wired yet; use -backend=memory for dev")
+	ctx, stop := signal.NotifyContext(context.Background(), syscall.SIGINT, syscall.SIGTERM)
+	defer stop()
+
+	sgn, err := buildSigner(*backend, *keyRefs, *keysFromEnv, logger)
+	if err != nil {
+		logger.Error("signer init", "err", err)
 		os.Exit(1)
-	default:
-		fmt.Fprintln(os.Stderr, "unknown -backend; expected memory|openbao")
-		os.Exit(2)
+	}
+
+	var validator token.Validator
+	if *pocketIDIssuer != "" {
+		pv, err := token.NewPocketIDValidator(ctx, *pocketIDIssuer, *pocketIDAudience)
+		if err != nil {
+			logger.Error("pocket-id init", "err", err)
+			os.Exit(1)
+		}
+		validator = pv
+		logger.Info("pocket-id validator wired", "issuer", *pocketIDIssuer, "audience", *pocketIDAudience)
+	} else {
+		validator = parseBearers(*bearers)
+		logger.Warn("signing-service: static bearer table in use — DEV ONLY")
+	}
+
+	var reviewer token.TokenReviewer
+	if strings.EqualFold(*k8sTokenReview, "on") {
+		tr, err := token.NewInClusterTokenReviewer()
+		if err != nil {
+			logger.Error("in-cluster tokenreview init", "err", err)
+			os.Exit(1)
+		}
+		reviewer = tr
+		logger.Info("k8s tokenreview wired")
+	}
+
+	var reg registry.Resolver
+	var pgReg *registry.Postgres
+	if *registryDSN != "" {
+		pr, err := registry.NewPostgres(ctx, *registryDSN)
+		if err != nil {
+			logger.Error("registry init", "err", err)
+			os.Exit(1)
+		}
+		reg = pr
+		pgReg = pr
+		logger.Info("trust-api registry wired")
+	}
+
+	var structured policy.StructuredDecider
+	if *policyBundle != "" {
+		opa, err := policy.NewOPAEvaluator(ctx, *policyBundle)
+		if err != nil {
+			logger.Error("opa policy init", "err", err)
+			os.Exit(1)
+		}
+		structured = opa
+		logger.Info("opa policy wired", "bundle", *policyBundle)
 	}
 
 	srv := httpapi.Server{
-		Signer:    sgn,
-		Policy:    policy.AllowAll{},
-		Validator: parseBearers(*bearers),
-		Logger:    logger,
-		Now:       time.Now,
+		Signer:           sgn,
+		Validator:        validator,
+		TokenReviewer:    reviewer,
+		Registry:         reg,
+		StructuredPolicy: structured,
+		Policy:           policy.AllowAll{},
+		Logger:           logger,
+		Now:              time.Now,
 	}
+
 	mux := http.NewServeMux()
 	srv.Mount(mux)
 
@@ -106,18 +147,64 @@ func main() {
 		ReadHeaderTimeout: 5 * time.Second,
 	}
 	go func() {
-		logger.Warn("signing-service: AllowAll policy and static bearers are DEV ONLY")
-		logger.Info("signing-service listening", "addr", *listen, "backend", *backend)
+		logger.Info("signing-service listening",
+			"addr", *listen,
+			"backend", *backend,
+			"pocket_id", *pocketIDIssuer != "",
+			"k8s_tokenreview", reviewer != nil,
+			"registry", reg != nil,
+			"opa", structured != nil,
+		)
+		if structured == nil || reg == nil || reviewer == nil {
+			logger.Warn("signing-service: structured double-identity path NOT fully wired",
+				"opa", structured != nil, "registry", reg != nil, "tokenreview", reviewer != nil)
+		}
 		if err := hsrv.ListenAndServe(); err != nil && err != http.ErrServerClosed {
 			logger.Error("http serve", "err", err)
 		}
 	}()
-	stop := make(chan os.Signal, 1)
-	signal.Notify(stop, syscall.SIGINT, syscall.SIGTERM)
-	<-stop
-	ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
+	<-ctx.Done()
+	shutdownCtx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
 	defer cancel()
-	_ = hsrv.Shutdown(ctx)
+	_ = hsrv.Shutdown(shutdownCtx)
+	if pgReg != nil {
+		pgReg.Close()
+	}
+}
+
+func buildSigner(backend, keyRefs string, keysFromEnv bool, logger *slog.Logger) (signer.Signer, error) {
+	switch backend {
+	case "memory":
+		mem := signer.NewInMemory()
+		for _, kr := range splitCSV(keyRefs) {
+			var priv ed25519.PrivateKey
+			if keysFromEnv {
+				envName := envNameForKey(kr)
+				raw := os.Getenv(envName)
+				if raw == "" {
+					return nil, fmt.Errorf("missing env %q for key_ref %q", envName, kr)
+				}
+				p, err := signer.DecodeHexEd25519Key(raw)
+				if err != nil {
+					return nil, fmt.Errorf("bad env key %q: %w", envName, err)
+				}
+				priv = p
+			} else {
+				_, p, err := ed25519.GenerateKey(rand.Reader)
+				if err != nil {
+					return nil, fmt.Errorf("gen key %q: %w", kr, err)
+				}
+				priv = p
+				logger.Warn("generated ephemeral dev key — not safe for prod", "key_ref", kr)
+			}
+			mem.AddKey(kr, priv)
+		}
+		return mem, nil
+	case "openbao":
+		return nil, fmt.Errorf("openbao backend not wired yet; use -backend=memory")
+	default:
+		return nil, fmt.Errorf("unknown -backend %q; expected memory|openbao", backend)
+	}
 }
 
 func splitCSV(s string) []string {

services/signing-service/go.mod

@@ -1,3 +1,45 @@
 module basicstack.de/proofedmesh/services/signing-service
 
-go 1.23
+go 1.26.0
+
+require (
+	github.com/coreos/go-oidc/v3 v3.21.0
+	github.com/jackc/pgx/v5 v5.11.0
+	github.com/open-policy-agent/opa v1.21.4
+)
+
+require (
+	github.com/agnivade/levenshtein v1.2.1 // indirect
+	github.com/cespare/xxhash/v2 v2.3.0 // indirect
+	github.com/decred/dcrd/dcrec/secp256k1/v4 v4.4.1 // indirect
+	github.com/go-jose/go-jose/v4 v4.1.4 // indirect
+	github.com/gobwas/glob v1.0.0 // indirect
+	github.com/goccy/go-json v0.10.6 // indirect
+	github.com/google/uuid v1.6.0 // indirect
+	github.com/jackc/pgpassfile v1.0.0 // indirect
+	github.com/jackc/pgservicefile v0.0.0-20240606120523-5a60cdf6a761 // indirect
+	github.com/jackc/puddle/v2 v2.2.2 // indirect
+	github.com/lestrrat-go/blackmagic v1.0.4 // indirect
+	github.com/lestrrat-go/dsig v1.4.0 // indirect
+	github.com/lestrrat-go/dsig-secp256k1 v1.0.0 // indirect
+	github.com/lestrrat-go/httpcc v1.0.1 // indirect
+	github.com/lestrrat-go/httprc/v3 v3.0.6 // indirect
+	github.com/lestrrat-go/jwx/v3 v3.3.0 // indirect
+	github.com/lestrrat-go/option/v2 v2.0.0 // indirect
+	github.com/rcrowley/go-metrics v0.0.0-20250401214520-65e299d6c5c9 // indirect
+	github.com/segmentio/asm v1.2.1 // indirect
+	github.com/sirupsen/logrus v1.10.2 // indirect
+	github.com/tchap/go-patricia/v2 v2.3.3 // indirect
+	github.com/valyala/fastjson v1.6.10 // indirect
+	github.com/vektah/gqlparser/v2 v2.5.37 // indirect
+	github.com/xeipuuv/gojsonpointer v0.0.0-20190905194746-02993c407bfb // indirect
+	github.com/xeipuuv/gojsonreference v0.0.0-20180127040603-bd5ef7bd5415 // indirect
+	github.com/yashtewari/glob-intersection v0.2.0 // indirect
+	go.yaml.in/yaml/v3 v3.0.5 // indirect
+	golang.org/x/crypto v0.57.0 // indirect
+	golang.org/x/oauth2 v0.36.0 // indirect
+	golang.org/x/sync v0.23.0 // indirect
+	golang.org/x/sys v0.48.0 // indirect
+	golang.org/x/text v0.42.0 // indirect
+	google.golang.org/protobuf v1.36.12 // indirect
+)

services/signing-service/go.sum

@@ -0,0 +1,144 @@
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+go.yaml.in/yaml/v3 v3.0.5 h1:N6y/pJk8buWs9NY5ERU2HSMfm+IuD/OtfdAnq6kESPw=
+go.yaml.in/yaml/v3 v3.0.5/go.mod h1:HVTZu1O7/Vkt2N+BFy8Zza+lnLsABggaTM2ZpNIGuKg=
+golang.org/x/crypto v0.57.0 h1:3ZVCjf8Ggz7zneR/EHRVx68Ctf+2pmIMP2UFhh9cC6M=
+golang.org/x/crypto v0.57.0/go.mod h1:Fdz0i5U6CoizGwLda9DttjSk6qlZo25zYNtR+ycvuZA=
+golang.org/x/mod v0.41.0 h1:qJmnOUb4YB+FsEuM3HcWucdZASCPGhsX6uljO6pog0c=
+golang.org/x/mod v0.41.0/go.mod h1:Ek9pY8RKWXwsWvd3rQiHYtMqkjSUV+s1Rj7j4H5Ur6o=
+golang.org/x/net v0.60.0 h1:79p50tfZlm0J9YfoDsSi639qSXNGVwEzOPLCxM2FsYU=
+golang.org/x/net v0.60.0/go.mod h1:2DA/G1UfVbCpQPeWTmMPGY7Cs2PkBkwu743bVX5PIVg=
+golang.org/x/oauth2 v0.36.0 h1:peZ/1z27fi9hUOFCAZaHyrpWG5lwe0RJEEEeH0ThlIs=
+golang.org/x/oauth2 v0.36.0/go.mod h1:YDBUJMTkDnJS+A4BP4eZBjCqtokkg1hODuPjwiGPO7Q=
+golang.org/x/sync v0.23.0 h1:KameEIfc1IkluZyXWLn39Wd4tURc6GbCiISGiZm2bQk=
+golang.org/x/sync v0.23.0/go.mod h1:sUUOizhqBxiL6pEWpqNLUiaJn1ShEbZ6BBqskPbjZm0=
+golang.org/x/sys v0.48.0 h1:bbX/i/6MgT9BVLM9RT1thmxL04yeTAhbEz4SyadbXoo=
+golang.org/x/sys v0.48.0/go.mod h1:hNLxWAXmnKAxqDtdwIYC4bM9oQPEecfsnNMuSxOs3og=
+golang.org/x/text v0.42.0 h1:JbOZXgfeCPU9gacVtYliJqOhD+zhrEqK4LfdpmlUZqI=
+golang.org/x/text v0.42.0/go.mod h1:ojzP1Z+2QtioaF8DTtO8K5q7JWVVYwZKenzujK0Zd0E=
+golang.org/x/tools v0.49.0 h1:3NI7VXzL9+1WZD52Dx2ttoPwD5DWrFGpl9mFZDlmisI=
+golang.org/x/tools v0.49.0/go.mod h1:SJNXV9DBKT0UbdttsQjbfJlAE/q+y36++zo3uL3N0Oo=
+google.golang.org/protobuf v1.36.12 h1:pJOKDDOyeXErUroCihFAd5LQuwXBSpVnKGrj5o/fwxc=
+google.golang.org/protobuf v1.36.12/go.mod h1:HTf+CrKn2C3g5S8VImy6tdcUvCska2kB7j23XfzDpco=
+gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
+gopkg.in/check.v1 v1.0.0-20201130134442-10cb98267c6c h1:Hei/4ADfdWqJk1ZMxUNpqntNwaWcugrBjAiHlqqRiVk=
+gopkg.in/check.v1 v1.0.0-20201130134442-10cb98267c6c/go.mod h1:JHkPIbrfpd72SG/EVd6muEfDQjcINNoR0C8j2r3qZ4Q=
+gopkg.in/yaml.v3 v3.0.0-20200313102051-9f266ea9e77c/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=

services/signing-service/internal/httpapi/sign.go

@@ -3,6 +3,7 @@
 package httpapi
 
 import (
+	"context"
 	"encoding/json"
 	"errors"
 	"fmt"
@@ -11,16 +12,49 @@ import (
 	"time"
 
 	"basicstack.de/proofedmesh/services/signing-service/internal/policy"
+	"basicstack.de/proofedmesh/services/signing-service/internal/registry"
 	"basicstack.de/proofedmesh/services/signing-service/internal/signer"
 	"basicstack.de/proofedmesh/services/signing-service/internal/token"
 )
 
+// Server composes the per-request pipeline:
+//
+//  1. Parse the Pocket-ID JWT from Authorization and resolve `sub`.
+//  2. If a TokenReviewer is configured, pull X-Workload-Token and resolve
+//     the authenticated (ns, sa). Omitted TokenReviewer disables the K8s
+//     side of the double-identity check — only useful for dev/CI.
+//  3. Resolve both identities against the agent registry; feed both rows
+//     to the structured policy. If no structured policy is wired, the
+//     legacy subject+keyRef Decider is used instead.
+//  4. Sign.
+//
+// Fields are plumbed through the struct so main.go can decide at startup
+// which backends to install.
 type Server struct {
 	Signer    signer.Signer
-	Policy    policy.Decider
 	Validator token.Validator
-	Logger    *slog.Logger
-	Now       func() time.Time
+
+	// TokenReviewer is OPTIONAL. When nil, the double-identity path is
+	// skipped and the policy input carries only the Pocket-ID side (the
+	// legacy Decider path is used instead).
+	TokenReviewer token.TokenReviewer
+
+	// Registry is OPTIONAL (and only consulted when both TokenReviewer
+	// and StructuredPolicy are present). The structured policy evaluates
+	// the two lookups it receives via Input.Registry.
+	Registry registry.Resolver
+
+	// StructuredPolicy is OPTIONAL. When present AND Registry/TokenReviewer
+	// are present, the handler uses the full double-identity flow. When
+	// nil, the handler falls back to the subject+keyRef Policy below.
+	StructuredPolicy policy.StructuredDecider
+
+	// Policy is the legacy subject+keyRef decider (AllowAll in dev,
+	// StructuredAdapter for prod wiring).
+	Policy policy.Decider
+
+	Logger *slog.Logger
+	Now    func() time.Time
 }
 
 func (s Server) Mount(mux *http.ServeMux) {
@@ -29,7 +63,7 @@ func (s Server) Mount(mux *http.ServeMux) {
 }
 
 type signRequest struct {
-	KeyRef    string          `json:"key_ref"`
+	KeyRef    string           `json:"key_ref"`
 	Statement signer.Statement `json:"statement"`
 }
 
@@ -89,14 +123,32 @@ func (s Server) handleSign(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
-	dec, err := s.Policy.Allow(ctx, subject, req.KeyRef)
-	if err != nil {
-		writeErr(w, http.StatusInternalServerError, "policy_eval_error", err.Error())
-		return
-	}
-	if !dec.Allow {
-		writeErr(w, http.StatusForbidden, "signing_denied", dec.Reason)
-		return
+	// Decide: structured double-identity path, or legacy subject+keyRef.
+	if s.useStructuredPath() {
+		dec, err := s.decideStructured(ctx, subject, req.KeyRef, r)
+		if err != nil {
+			var statusErr *httpStatusError
+			if errors.As(err, &statusErr) {
+				writeErr(w, statusErr.Status, statusErr.Code, statusErr.Message)
+				return
+			}
+			writeErr(w, http.StatusInternalServerError, "policy_eval_error", err.Error())
+			return
+		}
+		if !dec.Allow {
+			writeErr(w, http.StatusForbidden, "signing_denied", dec.Reason)
+			return
+		}
+	} else {
+		dec, err := s.Policy.Allow(ctx, subject, req.KeyRef)
+		if err != nil {
+			writeErr(w, http.StatusInternalServerError, "policy_eval_error", err.Error())
+			return
+		}
+		if !dec.Allow {
+			writeErr(w, http.StatusForbidden, "signing_denied", dec.Reason)
+			return
+		}
 	}
 
 	signed, err := signer.SignStatement(ctx, s.Signer, req.KeyRef, req.Statement)
@@ -114,7 +166,11 @@ func (s Server) handleSign(w http.ResponseWriter, r *http.Request) {
 	}
 
 	if s.Logger != nil {
-		s.Logger.Info("signed", "subject", subject, "key_ref", req.KeyRef, "content_hash", signed.ContentHash)
+		s.Logger.Info("signed",
+			"subject", subject,
+			"key_ref", req.KeyRef,
+			"content_hash", signed.ContentHash,
+		)
 	}
 
 	now := time.Now().UTC()
@@ -129,6 +185,66 @@ func (s Server) handleSign(w http.ResponseWriter, r *http.Request) {
 	})
 }
 
+func (s Server) useStructuredPath() bool {
+	return s.StructuredPolicy != nil && s.TokenReviewer != nil && s.Registry != nil
+}
+
+// decideStructured runs the full double-identity flow and hands the two
+// registry rows + both identities to the structured policy.
+func (s Server) decideStructured(ctx context.Context, pocketIDSub, keyRef string, r *http.Request) (policy.Decision, error) {
+	workloadToken, err := token.FromWorkloadHeader(r)
+	if err != nil {
+		return policy.Decision{}, &httpStatusError{
+			Status: http.StatusUnauthorized, Code: "unauthorized",
+			Message: "missing X-Workload-Token header",
+		}
+	}
+	k8sID, err := s.TokenReviewer.Review(ctx, workloadToken)
+	if err != nil {
+		if errors.Is(err, token.ErrWorkloadAuthFailed) || errors.Is(err, token.ErrNoWorkloadToken) {
+			return policy.Decision{}, &httpStatusError{
+				Status: http.StatusUnauthorized, Code: "unauthorized",
+				Message: fmt.Sprintf("workload token: %v", err),
+			}
+		}
+		return policy.Decision{}, fmt.Errorf("tokenreview: %w", err)
+	}
+
+	input := policy.Input{
+		PocketIDClient: pocketIDSub,
+		K8s: policy.InputK8s{
+			Namespace:      k8sID.Namespace,
+			ServiceAccount: k8sID.ServiceAccount,
+		},
+		KeyRef:   keyRef,
+		Registry: policy.InputRegistry{},
+	}
+
+	if byP, err := s.Registry.ByPocketID(ctx, pocketIDSub); err == nil {
+		input.Registry.ByPocketID = policy.FromAgent(byP)
+	} else if !errors.Is(err, registry.ErrNotFound) {
+		return policy.Decision{}, fmt.Errorf("registry.ByPocketID: %w", err)
+	}
+
+	if byK, err := s.Registry.ByK8sIdentity(ctx, k8sID.Namespace, k8sID.ServiceAccount); err == nil {
+		input.Registry.ByK8s = policy.FromAgent(byK)
+	} else if !errors.Is(err, registry.ErrNotFound) {
+		return policy.Decision{}, fmt.Errorf("registry.ByK8sIdentity: %w", err)
+	}
+
+	return s.StructuredPolicy.Decide(ctx, input)
+}
+
+// httpStatusError lets decideStructured return a 401 (not 500) when the
+// workload-identity side of the double-check fails.
+type httpStatusError struct {
+	Status  int
+	Code    string
+	Message string
+}
+
+func (e *httpStatusError) Error() string { return e.Message }
+
 func writeErr(w http.ResponseWriter, status int, code, message string) {
 	w.Header().Set("Content-Type", "application/json")
 	w.WriteHeader(status)

services/signing-service/internal/httpapi/sign_prod_test.go

@@ -0,0 +1,381 @@
+package httpapi
+
+import (
+	"bytes"
+	"context"
+	"crypto"
+	"crypto/ed25519"
+	"crypto/rand"
+	"crypto/rsa"
+	"crypto/sha256"
+	"encoding/base64"
+	"encoding/json"
+	"fmt"
+	"math/big"
+	"net/http"
+	"net/http/httptest"
+	"path/filepath"
+	"strings"
+	"testing"
+	"time"
+
+	"basicstack.de/proofedmesh/services/signing-service/internal/policy"
+	"basicstack.de/proofedmesh/services/signing-service/internal/registry"
+	"basicstack.de/proofedmesh/services/signing-service/internal/signer"
+	"basicstack.de/proofedmesh/services/signing-service/internal/token"
+)
+
+// mockPocketID issues RS256 JWTs and serves OIDC discovery + JWKS over
+// httptest so the signing-service's Pocket-ID validator thinks it is
+// talking to real Pocket ID. The suite exercises OIDC-Discovery +
+// JWK-Cache + kid rotation.
+type mockPocketID struct {
+	srv  *httptest.Server
+	keys map[string]*rsa.PrivateKey // active kid → key
+	// activeKIDs returns the order in which keys appear in the JWKS.
+	activeKIDs []string
+}
+
+func newMockPocketID(t *testing.T) *mockPocketID {
+	t.Helper()
+	m := &mockPocketID{keys: map[string]*rsa.PrivateKey{}}
+	k1, err := rsa.GenerateKey(rand.Reader, 2048)
+	if err != nil {
+		t.Fatal(err)
+	}
+	m.keys["k1"] = k1
+	m.activeKIDs = []string{"k1"}
+
+	mux := http.NewServeMux()
+	mux.HandleFunc("/.well-known/openid-configuration", func(w http.ResponseWriter, r *http.Request) {
+		w.Header().Set("Content-Type", "application/json")
+		fmt.Fprintf(w, `{
+			"issuer":"%s",
+			"authorization_endpoint":"%s/auth",
+			"token_endpoint":"%s/token",
+			"jwks_uri":"%s/jwks",
+			"id_token_signing_alg_values_supported":["RS256"]
+		}`, m.issuer(), m.issuer(), m.issuer(), m.issuer())
+	})
+	mux.HandleFunc("/jwks", func(w http.ResponseWriter, r *http.Request) {
+		w.Header().Set("Content-Type", "application/json")
+		var keys []map[string]any
+		for _, kid := range m.activeKIDs {
+			k := m.keys[kid]
+			n := base64.RawURLEncoding.EncodeToString(k.N.Bytes())
+			e := base64.RawURLEncoding.EncodeToString(big.NewInt(int64(k.E)).Bytes())
+			keys = append(keys, map[string]any{
+				"kty": "RSA", "use": "sig", "kid": kid, "alg": "RS256", "n": n, "e": e,
+			})
+		}
+		_ = json.NewEncoder(w).Encode(map[string]any{"keys": keys})
+	})
+	m.srv = httptest.NewServer(mux)
+	return m
+}
+
+func (m *mockPocketID) issuer() string { return m.srv.URL }
+
+func (m *mockPocketID) close() { m.srv.Close() }
+
+func (m *mockPocketID) rotateAddKey(t *testing.T, kid string) {
+	t.Helper()
+	k, err := rsa.GenerateKey(rand.Reader, 2048)
+	if err != nil {
+		t.Fatal(err)
+	}
+	m.keys[kid] = k
+	m.activeKIDs = append(m.activeKIDs, kid)
+}
+
+func (m *mockPocketID) signToken(t *testing.T, kid, sub, aud string) string {
+	t.Helper()
+	k, ok := m.keys[kid]
+	if !ok {
+		t.Fatalf("no key %q", kid)
+	}
+	header := map[string]any{"alg": "RS256", "typ": "JWT", "kid": kid}
+	claims := map[string]any{
+		"iss": m.issuer(),
+		"sub": sub,
+		"aud": aud,
+		"iat": time.Now().Unix(),
+		"exp": time.Now().Add(10 * time.Minute).Unix(),
+	}
+	hJ, _ := json.Marshal(header)
+	cJ, _ := json.Marshal(claims)
+	signingInput := base64.RawURLEncoding.EncodeToString(hJ) + "." + base64.RawURLEncoding.EncodeToString(cJ)
+	h := sha256.Sum256([]byte(signingInput))
+	sig, err := rsa.SignPKCS1v15(rand.Reader, k, crypto.SHA256, h[:])
+	if err != nil {
+		t.Fatal(err)
+	}
+	return signingInput + "." + base64.RawURLEncoding.EncodeToString(sig)
+}
+
+// ----- fake TokenReviewer -----
+
+func newFakeTokenReviewer(table map[string]token.K8sIdentity) token.TokenReviewer {
+	return token.StaticTokenReviewer(table)
+}
+
+// ----- fake registry seeded with Phase-1 Phase 1 agents -----
+
+func newPhase1Registry() registry.Resolver {
+	return registry.NewStatic([]registry.Agent{
+		{
+			AgentID:           "agent-approval-service",
+			PocketIDClient:    "agent-approval-service",
+			K8sNamespace:      "agent-trust",
+			K8sServiceAccount: "approval-service",
+			AllowedActions:    []string{"expense.submit"},
+		},
+		{
+			AgentID:           "agent-testagent-transform",
+			PocketIDClient:    "agent-testagent-transform",
+			K8sNamespace:      "agent-trust",
+			K8sServiceAccount: "testagent-transform",
+			AllowedActions:    []string{"expense.normalize", "expense.map_to_sink"},
+		},
+	})
+}
+
+func loadPolicy(t *testing.T) policy.StructuredDecider {
+	t.Helper()
+	p := filepath.Join("..", "..", "..", "..", "policies", "sinks", "signing_service.rego")
+	opa, err := policy.NewOPAEvaluator(context.Background(), p)
+	if err != nil {
+		t.Fatalf("load policy: %v", err)
+	}
+	return opa
+}
+
+// ----- harness wiring everything together -----
+
+type prodHarness struct {
+	hsrv            *httptest.Server
+	mockPID         *mockPocketID
+	approvalPub     ed25519.PublicKey
+	transformPub    ed25519.PublicKey
+	workloadToken   map[string]token.K8sIdentity
+	approvalBearer  string
+	transformBearer string
+}
+
+func newProdHarness(t *testing.T) *prodHarness {
+	t.Helper()
+	m := newMockPocketID(t)
+	t.Cleanup(m.close)
+
+	ctx := context.Background()
+	pv, err := token.NewPocketIDValidator(ctx, m.issuer(), "trust-api")
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	signerBackend := signer.NewInMemory()
+	_, approvalPriv, _ := ed25519.GenerateKey(rand.Reader)
+	signerBackend.AddKey("trust-api/approval-signer-2026-q4", approvalPriv)
+	_, transformPriv, _ := ed25519.GenerateKey(rand.Reader)
+	signerBackend.AddKey("trust-api/agent-testagent-transform-2026-q4", transformPriv)
+
+	wl := map[string]token.K8sIdentity{
+		"wl-approval":  {Namespace: "agent-trust", ServiceAccount: "approval-service"},
+		"wl-transform": {Namespace: "agent-trust", ServiceAccount: "testagent-transform"},
+	}
+
+	srv := Server{
+		Signer:           signerBackend,
+		Validator:        pv,
+		TokenReviewer:    newFakeTokenReviewer(wl),
+		Registry:         newPhase1Registry(),
+		StructuredPolicy: loadPolicy(t),
+		Policy:           policy.AllowAll{}, // unused in the structured path
+		Now:              func() time.Time { return time.Date(2026, 10, 25, 20, 0, 0, 0, time.UTC) },
+	}
+	mux := http.NewServeMux()
+	srv.Mount(mux)
+	hsrv := httptest.NewServer(mux)
+	t.Cleanup(hsrv.Close)
+
+	return &prodHarness{
+		hsrv:            hsrv,
+		mockPID:         m,
+		approvalPub:     approvalPriv.Public().(ed25519.PublicKey),
+		transformPub:    transformPriv.Public().(ed25519.PublicKey),
+		workloadToken:   wl,
+		approvalBearer:  m.signToken(t, "k1", "agent-approval-service", "trust-api"),
+		transformBearer: m.signToken(t, "k1", "agent-testagent-transform", "trust-api"),
+	}
+}
+
+func sign(h *prodHarness, bearer, workloadToken, body string) (*http.Response, error) {
+	req, _ := http.NewRequest("POST", h.hsrv.URL+"/api/v1/sign/dsse", bytes.NewBufferString(body))
+	req.Header.Set("Content-Type", "application/json")
+	req.Header.Set("Authorization", "Bearer "+bearer)
+	if workloadToken != "" {
+		req.Header.Set(token.WorkloadTokenHeader, workloadToken)
+	}
+	return http.DefaultClient.Do(req)
+}
+
+const approvalStatement = `{
+  "key_ref":"trust-api/approval-signer-2026-q4",
+  "statement":{
+    "_type":"https://in-toto.io/Statement/v1",
+    "subject":[{"name":"approval/APR-1","digest":{"sha256":"abcdef"}}],
+    "predicateType":"https://basicstack.de/attestations/approval/v1",
+    "predicate":{"approval_id":"APR-1"}
+  }
+}`
+
+const transformStatement = `{
+  "key_ref":"trust-api/agent-testagent-transform-2026-q4",
+  "statement":{
+    "_type":"https://in-toto.io/Statement/v1",
+    "subject":[{"name":"transform/TR-1","digest":{"sha256":"abcdef"}}],
+    "predicateType":"https://basicstack.de/attestations/transform/v1",
+    "predicate":{"transform_id":"TR-1"}
+  }
+}`
+
+// --- happy paths ---
+
+func TestProd_HappyPath_ApprovalService(t *testing.T) {
+	h := newProdHarness(t)
+	resp, err := sign(h, h.approvalBearer, "wl-approval", approvalStatement)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer resp.Body.Close()
+	if resp.StatusCode != http.StatusOK {
+		b, _ := jsonBody(resp)
+		t.Fatalf("status %d: %s", resp.StatusCode, b)
+	}
+	assertSignatureVerifies(t, resp, h.approvalPub, "application/vnd.in-toto+json")
+}
+
+func TestProd_HappyPath_TestAgentTransform(t *testing.T) {
+	h := newProdHarness(t)
+	resp, err := sign(h, h.transformBearer, "wl-transform", transformStatement)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer resp.Body.Close()
+	if resp.StatusCode != http.StatusOK {
+		b, _ := jsonBody(resp)
+		t.Fatalf("status %d: %s", resp.StatusCode, b)
+	}
+	assertSignatureVerifies(t, resp, h.transformPub, "application/vnd.in-toto+json")
+}
+
+// --- denies ---
+
+func TestProd_DeniesOnRegistryMismatch(t *testing.T) {
+	h := newProdHarness(t)
+	// Pocket-ID says Approval Service, but the X-Workload-Token is the
+	// transform agent's. Registry lookups land on different rows → 403.
+	resp, _ := sign(h, h.approvalBearer, "wl-transform", approvalStatement)
+	defer resp.Body.Close()
+	if resp.StatusCode != http.StatusForbidden {
+		t.Fatalf("expected 403 got %d", resp.StatusCode)
+	}
+	var e errResponse
+	_ = json.NewDecoder(resp.Body).Decode(&e)
+	if e.Error.Code != "signing_denied" {
+		t.Errorf("expected signing_denied code, got %q (%s)", e.Error.Code, e.Error.Message)
+	}
+}
+
+func TestProd_DeniesOnPolicyWrongKeyRef(t *testing.T) {
+	h := newProdHarness(t)
+	// Approval service identity on both sides, but asks for the transform
+	// agent's key_ref. Policy must deny.
+	body := strings.ReplaceAll(approvalStatement,
+		"trust-api/approval-signer-2026-q4",
+		"trust-api/agent-testagent-transform-2026-q4")
+	resp, _ := sign(h, h.approvalBearer, "wl-approval", body)
+	defer resp.Body.Close()
+	if resp.StatusCode != http.StatusForbidden {
+		t.Fatalf("expected 403 got %d", resp.StatusCode)
+	}
+}
+
+func TestProd_RejectsMissingWorkloadToken(t *testing.T) {
+	h := newProdHarness(t)
+	resp, _ := sign(h, h.approvalBearer, "", approvalStatement)
+	defer resp.Body.Close()
+	if resp.StatusCode != http.StatusUnauthorized {
+		t.Fatalf("expected 401 got %d", resp.StatusCode)
+	}
+}
+
+func TestProd_RejectsBadWorkloadToken(t *testing.T) {
+	h := newProdHarness(t)
+	resp, _ := sign(h, h.approvalBearer, "wl-does-not-exist", approvalStatement)
+	defer resp.Body.Close()
+	if resp.StatusCode != http.StatusUnauthorized {
+		t.Fatalf("expected 401 got %d", resp.StatusCode)
+	}
+}
+
+func TestProd_RejectsBadPocketIDToken(t *testing.T) {
+	h := newProdHarness(t)
+	resp, _ := sign(h, "not.a.jwt", "wl-approval", approvalStatement)
+	defer resp.Body.Close()
+	if resp.StatusCode != http.StatusUnauthorized {
+		t.Fatalf("expected 401 got %d", resp.StatusCode)
+	}
+}
+
+// --- kid rotation ---
+
+func TestProd_PocketID_KidRotation(t *testing.T) {
+	h := newProdHarness(t)
+	// Baseline works with k1.
+	resp, _ := sign(h, h.approvalBearer, "wl-approval", approvalStatement)
+	resp.Body.Close()
+	if resp.StatusCode != http.StatusOK {
+		t.Fatalf("baseline: expected 200 got %d", resp.StatusCode)
+	}
+	// Rotate: new kid k2 appears in JWKS. A token signed with k2 must verify
+	// after the validator refreshes the JWKS (go-oidc does this on kid miss).
+	h.mockPID.rotateAddKey(t, "k2")
+	bearer := h.mockPID.signToken(t, "k2", "agent-approval-service", "trust-api")
+	resp2, _ := sign(h, bearer, "wl-approval", approvalStatement)
+	defer resp2.Body.Close()
+	if resp2.StatusCode != http.StatusOK {
+		b, _ := jsonBody(resp2)
+		t.Fatalf("after rotation: expected 200 got %d: %s", resp2.StatusCode, b)
+	}
+}
+
+// --- helpers ---
+
+func jsonBody(resp *http.Response) (string, error) {
+	var buf bytes.Buffer
+	_, err := buf.ReadFrom(resp.Body)
+	return buf.String(), err
+}
+
+func assertSignatureVerifies(t *testing.T, resp *http.Response, pub ed25519.PublicKey, payloadType string) {
+	t.Helper()
+	var out signResponse
+	if err := json.NewDecoder(resp.Body).Decode(&out); err != nil {
+		t.Fatalf("decode: %v", err)
+	}
+	payload, err := base64.RawURLEncoding.DecodeString(out.Envelope.Payload)
+	if err != nil {
+		t.Fatalf("decode payload: %v", err)
+	}
+	pae := []byte(fmt.Sprintf("DSSEv1 %d %s %d ", len(payloadType), payloadType, len(payload)))
+	pae = append(pae, payload...)
+	sig, err := base64.RawURLEncoding.DecodeString(out.Envelope.Signatures[0].Sig)
+	if err != nil {
+		t.Fatalf("decode sig: %v", err)
+	}
+	if !ed25519.Verify(pub, pae, sig) {
+		t.Fatal("returned signature does not verify")
+	}
+}
+

services/signing-service/internal/policy/opa.go

@@ -0,0 +1,192 @@
+// OPA-backed policy decider for the signing-service.
+//
+// Loads a Rego policy file (default: policies/sinks/signing_service.rego)
+// at startup, compiles it once with the OPA Go SDK, and evaluates it per
+// request against the input the HTTP handler assembles from the two
+// identity lookups + the requested key_ref.
+package policy
+
+import (
+	"context"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"os"
+
+	"basicstack.de/proofedmesh/services/signing-service/internal/registry"
+	"github.com/open-policy-agent/opa/rego"
+)
+
+// Input is the structured input the signing-service HTTP handler builds
+// for every /api/v1/sign/dsse call. It is passed verbatim to Rego under
+// the top-level `input` document.
+type Input struct {
+	PocketIDClient string          `json:"pocket_id_client"`
+	K8s            InputK8s        `json:"k8s"`
+	KeyRef         string          `json:"key_ref"`
+	Registry       InputRegistry   `json:"registry"`
+}
+
+// InputK8s is the authenticated Kubernetes identity (from TokenReview).
+type InputK8s struct {
+	Namespace      string `json:"namespace"`
+	ServiceAccount string `json:"service_account"`
+}
+
+// InputRegistry carries both registry lookups (by pocket id + by k8s).
+// Each may be nil if the lookup returned ErrNotFound; the policy treats
+// a nil row as a hard identity failure.
+type InputRegistry struct {
+	ByPocketID *InputRegistryRow `json:"by_pocket_id"`
+	ByK8s      *InputRegistryRow `json:"by_k8s"`
+}
+
+// InputRegistryRow is a stripped-down `agents` row.
+type InputRegistryRow struct {
+	AgentID           string   `json:"agent_id"`
+	PocketIDClient    string   `json:"pocket_id_client"`
+	K8sNamespace      string   `json:"k8s_namespace"`
+	K8sServiceAccount string   `json:"k8s_service_account"`
+	AllowedActions    []string `json:"allowed_actions"`
+}
+
+// FromAgent builds a non-nil InputRegistryRow from a registry.Agent.
+func FromAgent(a registry.Agent) *InputRegistryRow {
+	return &InputRegistryRow{
+		AgentID:           a.AgentID,
+		PocketIDClient:    a.PocketIDClient,
+		K8sNamespace:      a.K8sNamespace,
+		K8sServiceAccount: a.K8sServiceAccount,
+		AllowedActions:    a.AllowedActions,
+	}
+}
+
+// StructuredDecider is a lower-level decider interface that policies that
+// need the full Input (not just subject/keyRef) implement. The signing
+// handler uses this when a StructuredDecider is wired; otherwise it falls
+// back to the subject/keyRef Decider.
+type StructuredDecider interface {
+	Decide(ctx context.Context, in Input) (Decision, error)
+}
+
+// OPAEvaluator is a StructuredDecider backed by an in-process Rego engine.
+type OPAEvaluator struct {
+	allow     rego.PreparedEvalQuery
+	denyReas  rego.PreparedEvalQuery
+	modulePkg string
+	src       string
+}
+
+// NewOPAEvaluator loads and compiles the Rego policy at path.
+// The policy package MUST be `proofedmesh.sinks.signing_service` (the
+// default policy file ships with that package name).
+func NewOPAEvaluator(ctx context.Context, path string) (*OPAEvaluator, error) {
+	src, err := os.ReadFile(path)
+	if err != nil {
+		return nil, fmt.Errorf("policy: read rego: %w", err)
+	}
+	return newOPAEvaluatorFromSource(ctx, path, string(src))
+}
+
+func newOPAEvaluatorFromSource(ctx context.Context, name, src string) (*OPAEvaluator, error) {
+	pkg := "proofedmesh.sinks.signing_service"
+	allowQ, err := rego.New(
+		rego.Query("data."+pkg+".allow"),
+		rego.Module(name, src),
+	).PrepareForEval(ctx)
+	if err != nil {
+		return nil, fmt.Errorf("policy: prepare allow: %w", err)
+	}
+	denyQ, err := rego.New(
+		rego.Query("data."+pkg+".deny_reason"),
+		rego.Module(name, src),
+	).PrepareForEval(ctx)
+	if err != nil {
+		return nil, fmt.Errorf("policy: prepare deny_reason: %w", err)
+	}
+	return &OPAEvaluator{allow: allowQ, denyReas: denyQ, modulePkg: pkg, src: src}, nil
+}
+
+// Decide evaluates the Rego policy against the given input.
+func (o *OPAEvaluator) Decide(ctx context.Context, in Input) (Decision, error) {
+	// Rego evaluates `input` as the parsed JSON-like document. Marshal
+	// through json tags to get deterministic snake_case keys.
+	raw, err := toRegoInput(in)
+	if err != nil {
+		return Decision{}, err
+	}
+	rs, err := o.allow.Eval(ctx, rego.EvalInput(raw))
+	if err != nil {
+		return Decision{}, fmt.Errorf("policy: eval allow: %w", err)
+	}
+	allowed := false
+	if len(rs) > 0 && len(rs[0].Expressions) > 0 {
+		if v, ok := rs[0].Expressions[0].Value.(bool); ok {
+			allowed = v
+		}
+	}
+	if allowed {
+		return Decision{Allow: true}, nil
+	}
+	// Collect deny_reason set for a usable 403 message.
+	drs, err := o.denyReas.Eval(ctx, rego.EvalInput(raw))
+	if err != nil {
+		return Decision{}, fmt.Errorf("policy: eval deny_reason: %w", err)
+	}
+	reason := "signing not permitted by policy"
+	if len(drs) > 0 && len(drs[0].Expressions) > 0 {
+		if arr, ok := drs[0].Expressions[0].Value.([]any); ok && len(arr) > 0 {
+			reason = joinReasons(arr)
+		}
+	}
+	return Decision{Allow: false, Reason: reason}, nil
+}
+
+// StructuredAdapter wraps a StructuredDecider so it also satisfies the
+// legacy subject+keyRef Decider contract (used by the HTTP layer's
+// fallback path and existing tests).
+type StructuredAdapter struct {
+	Decider StructuredDecider
+	Build   func(subject, keyRef string) Input
+}
+
+func (a StructuredAdapter) Allow(ctx context.Context, subject, keyRef string) (Decision, error) {
+	if a.Build == nil {
+		return Decision{}, errors.New("policy.StructuredAdapter: Build func is nil")
+	}
+	return a.Decider.Decide(ctx, a.Build(subject, keyRef))
+}
+
+func toRegoInput(in Input) (map[string]any, error) {
+	// Round-trip through JSON to collapse to anonymous maps/slices Rego
+	// handles directly, honouring our json tags (including nil-ness of
+	// *InputRegistryRow).
+	b, err := json.Marshal(in)
+	if err != nil {
+		return nil, fmt.Errorf("policy: marshal input: %w", err)
+	}
+	var out map[string]any
+	if err := json.Unmarshal(b, &out); err != nil {
+		return nil, fmt.Errorf("policy: unmarshal input: %w", err)
+	}
+	return out, nil
+}
+
+func joinReasons(arr []any) string {
+	// Keep this tiny; policy reasons are small sets of short strings.
+	out := ""
+	for i, v := range arr {
+		s, ok := v.(string)
+		if !ok {
+			continue
+		}
+		if i > 0 {
+			out += "; "
+		}
+		out += s
+	}
+	if out == "" {
+		return "signing not permitted by policy"
+	}
+	return out
+}

services/signing-service/internal/policy/opa_test.go

@@ -0,0 +1,147 @@
+package policy
+
+import (
+	"context"
+	"path/filepath"
+	"strings"
+	"testing"
+)
+
+// loadRealPolicy compiles the committed policies/sinks/signing_service.rego
+// so the tests fail if we rename the package or break the file.
+func loadRealPolicy(t *testing.T) *OPAEvaluator {
+	t.Helper()
+	// From services/signing-service, walk up to repo root (two parents),
+	// then into policies/sinks/signing_service.rego.
+	p := filepath.Join("..", "..", "..", "..", "policies", "sinks", "signing_service.rego")
+	opa, err := NewOPAEvaluator(context.Background(), p)
+	if err != nil {
+		t.Fatalf("load policy: %v", err)
+	}
+	return opa
+}
+
+func makeInput() Input {
+	by := InputRegistryRow{
+		AgentID:           "agent-approval-service",
+		PocketIDClient:    "agent-approval-service",
+		K8sNamespace:      "agent-trust",
+		K8sServiceAccount: "approval-service",
+		AllowedActions:    []string{"expense.submit"},
+	}
+	return Input{
+		PocketIDClient: "agent-approval-service",
+		K8s: InputK8s{
+			Namespace:      "agent-trust",
+			ServiceAccount: "approval-service",
+		},
+		KeyRef: "trust-api/approval-signer-2026-q4",
+		Registry: InputRegistry{
+			ByPocketID: &by,
+			ByK8s:      &by,
+		},
+	}
+}
+
+func TestOPA_Allows_ApprovalService_HappyPath(t *testing.T) {
+	opa := loadRealPolicy(t)
+	dec, err := opa.Decide(context.Background(), makeInput())
+	if err != nil {
+		t.Fatalf("Decide: %v", err)
+	}
+	if !dec.Allow {
+		t.Fatalf("expected allow, got deny: %q", dec.Reason)
+	}
+}
+
+func TestOPA_Allows_TestAgentTransform_HappyPath(t *testing.T) {
+	opa := loadRealPolicy(t)
+	by := InputRegistryRow{
+		AgentID:           "agent-testagent-transform",
+		PocketIDClient:    "agent-testagent-transform",
+		K8sNamespace:      "agent-trust",
+		K8sServiceAccount: "testagent-transform",
+	}
+	in := Input{
+		PocketIDClient: "agent-testagent-transform",
+		K8s:            InputK8s{Namespace: "agent-trust", ServiceAccount: "testagent-transform"},
+		KeyRef:         "trust-api/agent-testagent-transform-2026-q4",
+		Registry:       InputRegistry{ByPocketID: &by, ByK8s: &by},
+	}
+	dec, err := opa.Decide(context.Background(), in)
+	if err != nil {
+		t.Fatalf("Decide: %v", err)
+	}
+	if !dec.Allow {
+		t.Fatalf("expected allow, got deny: %q", dec.Reason)
+	}
+}
+
+func TestOPA_Denies_RegistryMismatch(t *testing.T) {
+	opa := loadRealPolicy(t)
+	in := makeInput()
+	// By-K8s returns a DIFFERENT agent row than By-PocketID — the double
+	// identity check must deny.
+	byK := InputRegistryRow{
+		AgentID:           "agent-testagent-transform",
+		PocketIDClient:    "agent-testagent-transform",
+		K8sNamespace:      "agent-trust",
+		K8sServiceAccount: "testagent-transform",
+	}
+	in.Registry.ByK8s = &byK
+	dec, err := opa.Decide(context.Background(), in)
+	if err != nil {
+		t.Fatalf("Decide: %v", err)
+	}
+	if dec.Allow {
+		t.Fatalf("expected deny on registry mismatch, got allow")
+	}
+	if !strings.Contains(dec.Reason, "do not resolve to the same registry agent") {
+		t.Errorf("unexpected reason: %q", dec.Reason)
+	}
+}
+
+func TestOPA_Denies_SubjectMismatchFromCaller(t *testing.T) {
+	opa := loadRealPolicy(t)
+	in := makeInput()
+	// Caller presented a different Pocket-ID subject than the one stored
+	// in the registry row — the policy must deny because the row no longer
+	// matches the authenticated identity.
+	in.PocketIDClient = "spoofed-client"
+	dec, err := opa.Decide(context.Background(), in)
+	if err != nil {
+		t.Fatalf("Decide: %v", err)
+	}
+	if dec.Allow {
+		t.Fatalf("expected deny when caller subject mismatches registry, got allow")
+	}
+}
+
+func TestOPA_Denies_WrongKeyRefForRole(t *testing.T) {
+	opa := loadRealPolicy(t)
+	in := makeInput()
+	in.KeyRef = "trust-api/agent-testagent-transform-2026-q4" // belongs to other agent
+	dec, err := opa.Decide(context.Background(), in)
+	if err != nil {
+		t.Fatalf("Decide: %v", err)
+	}
+	if dec.Allow {
+		t.Fatalf("expected deny on wrong key_ref, got allow")
+	}
+	if !strings.Contains(dec.Reason, "not permitted to sign") {
+		t.Errorf("unexpected reason: %q", dec.Reason)
+	}
+}
+
+func TestOPA_Denies_NilRegistryRow(t *testing.T) {
+	opa := loadRealPolicy(t)
+	in := makeInput()
+	in.Registry.ByK8s = nil
+	dec, err := opa.Decide(context.Background(), in)
+	if err != nil {
+		t.Fatalf("Decide: %v", err)
+	}
+	if dec.Allow {
+		t.Fatalf("expected deny on missing registry row, got allow")
+	}
+}

services/signing-service/internal/policy/policy.go

@@ -5,7 +5,6 @@ package policy
 
 import (
 	"context"
-	"errors"
 )
 
 // Decision carries both the boolean verdict and (on deny) a human-readable
@@ -27,11 +26,3 @@ func (AllowAll) Allow(_ context.Context, _, _ string) (Decision, error) {
 	return Decision{Allow: true}, nil
 }
 
-// OPA is a stub for the real Rego-backed policy evaluator.
-type OPA struct{}
-
-var errNotWired = errors.New("policy.OPA: not wired yet (follow-up subtask)")
-
-func (OPA) Allow(_ context.Context, _, _ string) (Decision, error) {
-	return Decision{}, errNotWired
-}

services/signing-service/internal/registry/registry.go

@@ -0,0 +1,125 @@
+// Package registry resolves ProofedMesh agent identities against the
+// trust-api `agents` table (db/trust/migrations/0002_agents.up.sql).
+//
+// The signing-service calls this package twice per request — once by
+// pocket_id_client (from the Pocket-ID JWT `sub` claim) and once by
+// (k8s_namespace, k8s_service_account) (from a Kubernetes TokenReview).
+// The results are handed to OPA which denies unless both lookups land on
+// the same, internally consistent agent row.
+package registry
+
+import (
+	"context"
+	"errors"
+	"fmt"
+
+	"github.com/jackc/pgx/v5"
+	"github.com/jackc/pgx/v5/pgxpool"
+)
+
+// ErrNotFound means no agent row matched the given identity. Callers
+// should treat this as a hard identity failure (403), never a 500.
+var ErrNotFound = errors.New("registry: agent not found")
+
+// Agent is the subset of the trust-api `agents` row that the signing
+// service needs for identity reconciliation and policy evaluation.
+type Agent struct {
+	AgentID           string
+	PocketIDClient    string
+	K8sNamespace      string
+	K8sServiceAccount string
+	DisplayName       string
+	AllowedActions    []string
+}
+
+// Resolver abstracts the backing store so tests can swap in an in-memory
+// implementation.
+type Resolver interface {
+	ByPocketID(ctx context.Context, client string) (Agent, error)
+	ByK8sIdentity(ctx context.Context, namespace, serviceAccount string) (Agent, error)
+}
+
+// Static is an in-memory resolver suitable for unit tests and the
+// never-happens case where we want to pin the signing-service to a
+// deterministic set of identities.
+type Static struct {
+	ByPocketIDMap    map[string]Agent
+	ByK8sIdentityMap map[string]Agent // key: ns + "/" + sa
+}
+
+// NewStatic builds a Static resolver from a slice of agents.
+func NewStatic(agents []Agent) *Static {
+	byP := make(map[string]Agent, len(agents))
+	byK := make(map[string]Agent, len(agents))
+	for _, a := range agents {
+		byP[a.PocketIDClient] = a
+		byK[a.K8sNamespace+"/"+a.K8sServiceAccount] = a
+	}
+	return &Static{ByPocketIDMap: byP, ByK8sIdentityMap: byK}
+}
+
+func (s *Static) ByPocketID(_ context.Context, client string) (Agent, error) {
+	a, ok := s.ByPocketIDMap[client]
+	if !ok {
+		return Agent{}, ErrNotFound
+	}
+	return a, nil
+}
+
+func (s *Static) ByK8sIdentity(_ context.Context, namespace, serviceAccount string) (Agent, error) {
+	a, ok := s.ByK8sIdentityMap[namespace+"/"+serviceAccount]
+	if !ok {
+		return Agent{}, ErrNotFound
+	}
+	return a, nil
+}
+
+// Postgres is the production resolver, backed by the trust-api database.
+type Postgres struct {
+	pool *pgxpool.Pool
+}
+
+// NewPostgres opens a connection pool at the given DSN. Caller owns Close.
+func NewPostgres(ctx context.Context, dsn string) (*Postgres, error) {
+	pool, err := pgxpool.New(ctx, dsn)
+	if err != nil {
+		return nil, fmt.Errorf("registry: pgxpool.New: %w", err)
+	}
+	return &Postgres{pool: pool}, nil
+}
+
+// Close releases the pool.
+func (p *Postgres) Close() {
+	if p.pool != nil {
+		p.pool.Close()
+	}
+}
+
+const selectCols = `agent_id, pocket_id_client, k8s_namespace, k8s_service_account, display_name, allowed_actions`
+
+func (p *Postgres) ByPocketID(ctx context.Context, client string) (Agent, error) {
+	row := p.pool.QueryRow(ctx, `SELECT `+selectCols+` FROM agents WHERE pocket_id_client = $1`, client)
+	return scanAgent(row)
+}
+
+func (p *Postgres) ByK8sIdentity(ctx context.Context, namespace, serviceAccount string) (Agent, error) {
+	row := p.pool.QueryRow(ctx,
+		`SELECT `+selectCols+` FROM agents WHERE k8s_namespace = $1 AND k8s_service_account = $2`,
+		namespace, serviceAccount)
+	return scanAgent(row)
+}
+
+type scannable interface {
+	Scan(dest ...any) error
+}
+
+func scanAgent(row scannable) (Agent, error) {
+	var a Agent
+	if err := row.Scan(&a.AgentID, &a.PocketIDClient, &a.K8sNamespace, &a.K8sServiceAccount, &a.DisplayName, &a.AllowedActions); err != nil {
+		if errors.Is(err, pgx.ErrNoRows) {
+			return Agent{}, ErrNotFound
+		}
+		return Agent{}, fmt.Errorf("registry: scan: %w", err)
+	}
+	return a, nil
+}

services/signing-service/internal/registry/registry_test.go

@@ -0,0 +1,29 @@
+package registry
+
+import (
+	"context"
+	"errors"
+	"testing"
+)
+
+func TestStatic_LookupBothWays(t *testing.T) {
+	s := NewStatic([]Agent{
+		{AgentID: "agent-approval-service", PocketIDClient: "agent-approval-service", K8sNamespace: "agent-trust", K8sServiceAccount: "approval-service"},
+		{AgentID: "agent-testagent-transform", PocketIDClient: "agent-testagent-transform", K8sNamespace: "agent-trust", K8sServiceAccount: "testagent-transform"},
+	})
+	ctx := context.Background()
+	got, err := s.ByPocketID(ctx, "agent-approval-service")
+	if err != nil || got.AgentID != "agent-approval-service" {
+		t.Fatalf("ByPocketID: got %+v, err %v", got, err)
+	}
+	got, err = s.ByK8sIdentity(ctx, "agent-trust", "testagent-transform")
+	if err != nil || got.AgentID != "agent-testagent-transform" {
+		t.Fatalf("ByK8sIdentity: got %+v, err %v", got, err)
+	}
+	if _, err := s.ByPocketID(ctx, "nope"); !errors.Is(err, ErrNotFound) {
+		t.Fatalf("expected ErrNotFound, got %v", err)
+	}
+	if _, err := s.ByK8sIdentity(ctx, "agent-trust", "nope"); !errors.Is(err, ErrNotFound) {
+		t.Fatalf("expected ErrNotFound, got %v", err)
+	}
+}

services/signing-service/internal/token/k8s_tokenreview.go

@@ -0,0 +1,223 @@
+// Kubernetes TokenReview-backed workload-identity validator.
+//
+// The signing-service receives the workload's projected ServiceAccount
+// token in the `X-Workload-Token` header. We submit that token to the
+// cluster via `authentication.k8s.io/v1 TokenReview` using the pod's own
+// in-cluster credentials, and return the authenticated
+// `system:serviceaccount:<ns>:<sa>` as (namespace, serviceAccount).
+//
+// This file deliberately does not import k8s.io/client-go to keep the
+// dependency surface narrow; a hand-rolled HTTPS POST against the API
+// server is all that's required.
+package token
+
+import (
+	"bytes"
+	"context"
+	"crypto/tls"
+	"crypto/x509"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"io"
+	"net/http"
+	"os"
+	"strings"
+	"time"
+)
+
+const (
+	// WorkloadTokenHeader is the HTTP header carrying the workload's
+	// projected SA token (not the Authorization header).
+	WorkloadTokenHeader = "X-Workload-Token"
+
+	defaultSATokenPath = "/var/run/secrets/kubernetes.io/serviceaccount/token"
+	defaultCAPath      = "/var/run/secrets/kubernetes.io/serviceaccount/ca.crt"
+)
+
+// ErrNoWorkloadToken is returned when the X-Workload-Token header is
+// missing. Caller MUST map this to a 401.
+var ErrNoWorkloadToken = errors.New("tokenreview: missing X-Workload-Token header")
+
+// ErrWorkloadAuthFailed is returned when TokenReview reports the token is
+// invalid or unauthenticated. Caller MUST map this to a 401.
+var ErrWorkloadAuthFailed = errors.New("tokenreview: workload token not authenticated")
+
+// K8sIdentity is the subset of a TokenReview UserInfo we care about.
+type K8sIdentity struct {
+	Namespace      string
+	ServiceAccount string
+	// UID is the ServiceAccount's UID (useful for audit; may be empty for
+	// non-SA callers which should be rejected before this type is built).
+	UID string
+}
+
+// TokenReviewer validates a workload-presented token and returns the
+// authenticated ServiceAccount identity.
+type TokenReviewer interface {
+	Review(ctx context.Context, workloadToken string) (K8sIdentity, error)
+}
+
+// FromWorkloadHeader extracts the workload token from the X-Workload-Token
+// header; it does NOT accept Bearer prefixes because this header is
+// documented as raw-token.
+func FromWorkloadHeader(r *http.Request) (string, error) {
+	t := strings.TrimSpace(r.Header.Get(WorkloadTokenHeader))
+	if t == "" {
+		return "", ErrNoWorkloadToken
+	}
+	return t, nil
+}
+
+// StaticTokenReviewer is a test seam: a fixed table from workload token
+// → identity. All production paths use K8sTokenReviewer.
+type StaticTokenReviewer map[string]K8sIdentity
+
+func (s StaticTokenReviewer) Review(_ context.Context, workloadToken string) (K8sIdentity, error) {
+	id, ok := s[workloadToken]
+	if !ok {
+		return K8sIdentity{}, ErrWorkloadAuthFailed
+	}
+	return id, nil
+}
+
+// K8sTokenReviewer talks to a Kubernetes API server.
+type K8sTokenReviewer struct {
+	APIServer   string // e.g. "https://kubernetes.default.svc"
+	BearerToken string // pod's own SA token (not the workload token)
+	HTTPClient  *http.Client
+}
+
+// NewInClusterTokenReviewer loads the pod's SA token and the cluster CA
+// from the standard in-cluster paths and wires up a TLS-pinned client.
+// The returned reviewer talks to `https://kubernetes.default.svc`.
+func NewInClusterTokenReviewer() (*K8sTokenReviewer, error) {
+	return NewTokenReviewerFromPaths(
+		"https://kubernetes.default.svc",
+		defaultSATokenPath,
+		defaultCAPath,
+	)
+}
+
+// NewTokenReviewerFromPaths loads SA token & CA from explicit paths; the
+// in-cluster helper above is a thin wrapper.
+func NewTokenReviewerFromPaths(apiServer, tokenPath, caPath string) (*K8sTokenReviewer, error) {
+	tokenBytes, err := os.ReadFile(tokenPath)
+	if err != nil {
+		return nil, fmt.Errorf("tokenreview: read SA token: %w", err)
+	}
+	caBytes, err := os.ReadFile(caPath)
+	if err != nil {
+		return nil, fmt.Errorf("tokenreview: read CA: %w", err)
+	}
+	pool := x509.NewCertPool()
+	if !pool.AppendCertsFromPEM(caBytes) {
+		return nil, errors.New("tokenreview: CA pem invalid")
+	}
+	hc := &http.Client{
+		Timeout: 5 * time.Second,
+		Transport: &http.Transport{
+			TLSClientConfig: &tls.Config{RootCAs: pool, MinVersion: tls.VersionTLS12},
+		},
+	}
+	return &K8sTokenReviewer{
+		APIServer:   apiServer,
+		BearerToken: strings.TrimSpace(string(tokenBytes)),
+		HTTPClient:  hc,
+	}, nil
+}
+
+// tokenReviewRequest / tokenReviewResponse mirror just the fields we
+// read, so we don't pull in client-go's typed meta.
+type tokenReviewRequest struct {
+	APIVersion string                 `json:"apiVersion"`
+	Kind       string                 `json:"kind"`
+	Spec       tokenReviewRequestSpec `json:"spec"`
+}
+
+type tokenReviewRequestSpec struct {
+	Token string `json:"token"`
+}
+
+type tokenReviewResponse struct {
+	Status tokenReviewStatus `json:"status"`
+}
+
+type tokenReviewStatus struct {
+	Authenticated bool                `json:"authenticated"`
+	User          tokenReviewUserInfo `json:"user"`
+	Error         string              `json:"error"`
+}
+
+type tokenReviewUserInfo struct {
+	Username string `json:"username"`
+	UID      string `json:"uid"`
+}
+
+func (r *K8sTokenReviewer) Review(ctx context.Context, workloadToken string) (K8sIdentity, error) {
+	if workloadToken == "" {
+		return K8sIdentity{}, ErrNoWorkloadToken
+	}
+	payload := tokenReviewRequest{
+		APIVersion: "authentication.k8s.io/v1",
+		Kind:       "TokenReview",
+		Spec:       tokenReviewRequestSpec{Token: workloadToken},
+	}
+	body, err := json.Marshal(payload)
+	if err != nil {
+		return K8sIdentity{}, fmt.Errorf("tokenreview: marshal: %w", err)
+	}
+	url := strings.TrimRight(r.APIServer, "/") + "/apis/authentication.k8s.io/v1/tokenreviews"
+	req, err := http.NewRequestWithContext(ctx, "POST", url, bytes.NewReader(body))
+	if err != nil {
+		return K8sIdentity{}, fmt.Errorf("tokenreview: build request: %w", err)
+	}
+	req.Header.Set("Authorization", "Bearer "+r.BearerToken)
+	req.Header.Set("Content-Type", "application/json")
+	req.Header.Set("Accept", "application/json")
+	resp, err := r.HTTPClient.Do(req)
+	if err != nil {
+		return K8sIdentity{}, fmt.Errorf("tokenreview: POST: %w", err)
+	}
+	defer resp.Body.Close()
+	raw, _ := io.ReadAll(io.LimitReader(resp.Body, 1<<20))
+	if resp.StatusCode/100 != 2 {
+		return K8sIdentity{}, fmt.Errorf("tokenreview: api server %d: %s", resp.StatusCode, truncate(string(raw), 256))
+	}
+	var out tokenReviewResponse
+	if err := json.Unmarshal(raw, &out); err != nil {
+		return K8sIdentity{}, fmt.Errorf("tokenreview: decode: %w", err)
+	}
+	if !out.Status.Authenticated {
+		if out.Status.Error != "" {
+			return K8sIdentity{}, fmt.Errorf("%w: %s", ErrWorkloadAuthFailed, out.Status.Error)
+		}
+		return K8sIdentity{}, ErrWorkloadAuthFailed
+	}
+	ns, sa, ok := parseSAUsername(out.Status.User.Username)
+	if !ok {
+		return K8sIdentity{}, fmt.Errorf("%w: not a ServiceAccount: %q", ErrWorkloadAuthFailed, out.Status.User.Username)
+	}
+	return K8sIdentity{Namespace: ns, ServiceAccount: sa, UID: out.Status.User.UID}, nil
+}
+
+// parseSAUsername extracts (ns, sa) from `system:serviceaccount:<ns>:<sa>`.
+func parseSAUsername(u string) (string, string, bool) {
+	const prefix = "system:serviceaccount:"
+	if !strings.HasPrefix(u, prefix) {
+		return "", "", false
+	}
+	rest := u[len(prefix):]
+	i := strings.IndexByte(rest, ':')
+	if i <= 0 || i == len(rest)-1 {
+		return "", "", false
+	}
+	return rest[:i], rest[i+1:], true
+}
+
+func truncate(s string, n int) string {
+	if len(s) <= n {
+		return s
+	}
+	return s[:n] + "…"
+}

services/signing-service/internal/token/pocket_id.go

@@ -0,0 +1,76 @@
+// Pocket-ID OIDC-backed Bearer token validator.
+//
+// Phase 1 wires this up for the production path: the signing-service
+// discovers the issuer, caches the JWKS, and auto-refreshes on `kid`
+// rotation via coreos/go-oidc's RemoteKeySet.
+package token
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"net/http"
+	"time"
+
+	"github.com/coreos/go-oidc/v3/oidc"
+)
+
+// PocketIDValidator verifies a Bearer JWT against a Pocket-ID issuer and
+// returns the `sub` claim (which is the Pocket-ID client id).
+type PocketIDValidator struct {
+	verifier *oidc.IDTokenVerifier
+	issuer   string
+	audience string
+}
+
+// NewPocketIDValidator performs OIDC discovery and returns a validator.
+// If audience is non-empty, the verifier enforces the `aud` claim.
+// SkipClientIDCheck is used when audience is empty because Pocket ID
+// subject tokens may be addressed to a service name rather than a client.
+func NewPocketIDValidator(ctx context.Context, issuer, audience string) (*PocketIDValidator, error) {
+	if issuer == "" {
+		return nil, errors.New("token.PocketID: empty issuer")
+	}
+	provider, err := oidc.NewProvider(ctx, issuer)
+	if err != nil {
+		return nil, fmt.Errorf("token.PocketID: oidc discovery for %q: %w", issuer, err)
+	}
+	cfg := &oidc.Config{
+		ClientID:          audience,
+		SkipClientIDCheck: audience == "",
+	}
+	v := provider.Verifier(cfg)
+	return &PocketIDValidator{verifier: v, issuer: issuer, audience: audience}, nil
+}
+
+// Validate implements Validator. It parses, verifies and returns `sub`.
+func (p *PocketIDValidator) Validate(ctx context.Context, bearer string) (string, error) {
+	if bearer == "" {
+		return "", ErrInvalid
+	}
+	idTok, err := p.verifier.Verify(ctx, bearer)
+	if err != nil {
+		return "", fmt.Errorf("%w: %v", ErrInvalid, err)
+	}
+	if idTok.Subject == "" {
+		return "", fmt.Errorf("%w: missing sub claim", ErrInvalid)
+	}
+	return idTok.Subject, nil
+}
+
+// Issuer returns the configured issuer URL (for logs / healthz).
+func (p *PocketIDValidator) Issuer() string { return p.issuer }
+
+// NewPocketIDValidatorWithHTTPClient is the same as NewPocketIDValidator
+// but uses the supplied HTTP client (test seams, custom timeouts).
+func NewPocketIDValidatorWithHTTPClient(ctx context.Context, issuer, audience string, client *http.Client) (*PocketIDValidator, error) {
+	if client != nil {
+		ctx = oidc.ClientContext(ctx, client)
+	}
+	return NewPocketIDValidator(ctx, issuer, audience)
+}
+
+// SignerRefreshInterval is advisory — go-oidc refreshes on `kid` miss but
+// callers who want proactive refresh can wrap this in a timer. We expose
+// it so cmd/ can decide a cadence.
+const SignerRefreshInterval = 15 * time.Minute

services/signing-service/internal/token/validator.go

@@ -32,13 +32,6 @@ func (s Static) Validate(_ context.Context, bearer string) (string, error) {
 	return sub, nil
 }
 
-// PocketID is a stub for a JWKS-based Pocket ID token verifier.
-type PocketID struct{}
-
-func (PocketID) Validate(_ context.Context, _ string) (string, error) {
-	return "", errors.New("token.PocketID: not wired yet (follow-up subtask)")
-}
-
 // FromAuthHeader extracts the bearer from an "Authorization: Bearer …" header.
 func FromAuthHeader(r *http.Request) (string, error) {
 	h := r.Header.Get("Authorization")

services/testagent-transform/Dockerfile

@@ -0,0 +1,35 @@
+# syntax=docker/dockerfile:1.7
+
+# ---------- build ----------
+FROM golang:1.23-alpine3.21 AS build
+
+ENV CGO_ENABLED=0 \
+    GOOS=linux \
+    GOFLAGS="-trimpath"
+
+WORKDIR /src
+
+COPY services/testagent-transform/go.mod ./services/testagent-transform/
+RUN --mount=type=cache,target=/root/.cache/go-build \
+    --mount=type=cache,target=/go/pkg/mod \
+    cd services/testagent-transform && go mod download
+
+COPY services/testagent-transform/ ./services/testagent-transform/
+
+WORKDIR /src/services/testagent-transform
+RUN --mount=type=cache,target=/root/.cache/go-build \
+    --mount=type=cache,target=/go/pkg/mod \
+    go vet ./... && \
+    go test ./... && \
+    go build -ldflags="-s -w" -o /out/testagent-transform ./cmd/testagent-transform
+
+# ---------- runtime ----------
+# Distroless static+nonroot. The projected ServiceAccount token lives on
+# a tmpfs volume mounted by kubelet into /var/run/secrets/tokens/trust-api,
+# so the container only needs read access to that path at runtime.
+FROM gcr.io/distroless/static-debian12:nonroot
+
+COPY --from=build /out/testagent-transform /testagent-transform
+
+USER 65532:65532
+ENTRYPOINT ["/testagent-transform"]

services/testagent-transform/README.md

@@ -0,0 +1,105 @@
+# testagent-transform
+
+Phase-1 end-to-end demonstrator of the ProofedMesh trust chain's **Transform**
+step ([DEV-610](/DEV/issues/DEV-610), parent
+[DEV-606](/DEV/issues/DEV-606)). It is a one-shot CLI, not an HTTP service:
+given an approval attestation and a `handover_payload`, it produces a signed
+transform attestation, logs it to the transparency-log, and hands the payload
+to the Phase-1 dummy-sink. The exit code is 0 on success.
+
+## Flow
+
+1. **Fetch approval.** `GET {TRANSFORM_TLOG_URL}/api/v1/log/entries/{approval_ref}`.
+   The TLog returns the stored DSSE envelope plus `log_index`.
+2. **Verify.** The returned envelope is DSSE-verified against the pinned
+   approval-signer keyring (`APPROVAL_SIGNER_KEYS`). On failure the agent
+   stops before any signing call — nothing new is attested on top of an
+   untrusted approval.
+3. **Build transform statement.** in-toto v1 Statement with
+   `predicateType = https://basicstack.de/attestations/transform/v1`,
+   `operation = expense.map_to_sink`, `materials[0].attestation_ref =
+   approval_ref`, and `subject[0].digest.sha256 = sha256(canonical(handover_payload))`.
+   `canonical` here is byte-identical to the approval-service's canonical
+   serialisation so a downstream verifier reproduces the same hash.
+4. **Sign.** `POST {TRANSFORM_SIGNING_URL}/api/v1/sign/dsse` with BOTH
+   identities set as headers:
+   - `Authorization: Bearer <pocket-id-access-token>`  (`client_credentials`
+     grant against `POCKET_ID_ISSUER`)
+   - `X-Workload-Token: <projected-sa-token>`  (read from
+     `TRANSFORM_WORKLOAD_TOKEN_PATH`, default
+     `/var/run/secrets/tokens/trust-api`)
+   The signing-service's structured policy evaluates BOTH identities against
+   the agent registry and OPA; a Pocket-ID bearer alone is not enough. See
+   `services/signing-service/internal/httpapi/sign.go`.
+5. **Log.** `POST {TRANSFORM_TLOG_URL}/api/v1/log/entries` with the
+   envelope + `content_hash` from step 4.
+6. **Handover.** `POST {TRANSFORM_SINK_URL}/api/v1/handover` with the
+   canonical `handover_payload` bytes. Headers set:
+   - `X-Payload-Schema: sink.dummy.v1`
+   - `X-Attestation-Ref: <transform content_hash>`
+
+## Non-scope
+
+- No read-side attestations (Phase 2).
+- No persistent store; the agent is stateless and idempotent given the same
+  `(approval_ref, handover_payload)` input (the TLog deduplicates on
+  `content_hash`).
+
+## Configuration
+
+| Env var                              | Default                                                       | Purpose                                                    |
+| ------------------------------------ | ------------------------------------------------------------- | ---------------------------------------------------------- |
+| `TRANSFORM_TLOG_URL`                 | *(required)*                                                  | Base URL of transparency-log.                              |
+| `TRANSFORM_SIGNING_URL`              | *(required)*                                                  | Base URL of signing-service.                               |
+| `TRANSFORM_SINK_URL`                 | *(required)*                                                  | Base URL of dummy-sink.                                    |
+| `TRANSFORM_WORKLOAD_TOKEN_PATH`      | `/var/run/secrets/tokens/trust-api`                           | Projected ServiceAccount token path.                       |
+| `POCKET_ID_ISSUER`                   | *(required)*                                                  | Pocket-ID OIDC issuer URL.                                 |
+| `POCKET_ID_CLIENT_ID`                | *(required)*                                                  | OIDC client id for this agent.                             |
+| `POCKET_ID_CLIENT_SECRET`            | *(required)*                                                  | OIDC client secret for this agent.                         |
+| `POCKET_ID_AUDIENCE`                 | `trust-api`                                                   | OIDC token audience.                                       |
+| `APPROVAL_SIGNER_KEYS`               | *(required)*                                                  | Comma-separated `kid=base64(public-ed25519)` entries.      |
+| `TRANSFORM_ACTOR`                    | `agent-testagent-transform`                                   | Registry id written into the attestation.                  |
+| `TRANSFORM_OPERATION`                | `expense.map_to_sink`                                         | Transform operation name (must match OPA policy).          |
+| `TRANSFORM_SINK_TARGET`              | `sink:dummy-sink`                                             | Logical sink identifier.                                   |
+| `TRANSFORM_SIGNING_KEY_REF`          | `trust-api/agent-testagent-transform-2026-q4`                 | OpenBao Transit key ref for the transform signer.          |
+| `TRANSFORM_INPUT_SCHEMA` / `_VERSION`   | `expense.canonical` / `1.2.0`                              | Input schema name/version carried in the attestation.      |
+| `TRANSFORM_OUTPUT_SCHEMA` / `_VERSION`  | `sink.db.expense` / `1.2.0`                                | Output schema name/version carried in the attestation.     |
+| `TRANSFORM_VERSION`                  | `0.1.0`                                                       | Agent's own version string, carried in the attestation.    |
+| `TRANSFORM_SINK_PAYLOAD_SCHEMA`      | `sink.dummy.v1`                                               | Value sent on the sink's `X-Payload-Schema` header.        |
+
+## CLI
+
+```
+testagent-transform \
+  -workflow     WF-0042 \
+  -approval-ref sha256:... \
+  -handover     ./handover.json
+```
+
+`handover.json` must be a JSON object; the agent canonicalises it before
+hashing + sending to the sink.
+
+## Tests
+
+```
+cd services/testagent-transform
+go vet ./...
+go test ./...
+```
+
+The end-to-end `transform` tests spin up four `httptest` servers — approval
+read, signing-service, transparency-log, dummy-sink — and run the full
+pipeline against them:
+
+- **Happy path.** All four backends respond; the subject digest the agent
+  signs equals the sha256 of the canonical bytes POSTed to the sink; the
+  TLog's recorded content_hash equals the agent's returned `TransformRef`.
+- **Invalid approval signature.** The approval mock returns a DSSE envelope
+  whose Ed25519 signature does not verify against the pinned public key.
+  The agent fails with `ErrInvalidApproval` and never calls the
+  signing-service, TLog, or sink.
+- **Signing denied.** The signing-service answers `403 signing_denied`.
+  The agent surfaces `signer.ErrSigningDenied` and never calls the TLog or
+  sink.
+- **Missing Pocket-ID token.** The TokenSource returns `""`. The signer
+  client rejects before any network traffic.

services/testagent-transform/cmd/testagent-transform/main.go

@@ -0,0 +1,227 @@
+// Command testagent-transform is the Phase-1 end-to-end demonstrator of
+// the ProofedMesh trust chain's Transform step. It is intentionally a
+// one-shot CLI: given an approval attestation_ref + a handover_payload,
+// it fetches/verifies the approval, builds a transform attestation,
+// signs it against the signing-service with BOTH identities, logs the
+// envelope to the transparency-log, and POSTs the handover_payload bytes
+// to the dummy-sink. The exit code is 0 on success, non-zero on any error.
+//
+// See services/testagent-transform/README.md for how env vars map to the
+// Runner wiring and how the agent reads its two identities.
+package main
+
+import (
+	"context"
+	"crypto/ed25519"
+	"encoding/base64"
+	"encoding/hex"
+	"encoding/json"
+	"errors"
+	"flag"
+	"fmt"
+	"log/slog"
+	"os"
+	"strings"
+	"time"
+
+	"basicstack.de/proofedmesh/services/testagent-transform/internal/approval"
+	"basicstack.de/proofedmesh/services/testagent-transform/internal/auth"
+	"basicstack.de/proofedmesh/services/testagent-transform/internal/dsse"
+	"basicstack.de/proofedmesh/services/testagent-transform/internal/signer"
+	"basicstack.de/proofedmesh/services/testagent-transform/internal/sink"
+	"basicstack.de/proofedmesh/services/testagent-transform/internal/tlog"
+	"basicstack.de/proofedmesh/services/testagent-transform/internal/transform"
+)
+
+func main() {
+	if err := run(context.Background(), os.Args[1:]); err != nil {
+		fmt.Fprintln(os.Stderr, "testagent-transform:", err)
+		os.Exit(1)
+	}
+}
+
+func run(ctx context.Context, args []string) error {
+	fs := flag.NewFlagSet("testagent-transform", flag.ContinueOnError)
+	var (
+		workflowID      = fs.String("workflow", "", "workflow id to tag on the transform attestation")
+		approvalRef     = fs.String("approval-ref", "", "sha256:<hex> content_hash of the approval attestation to fetch")
+		handoverPath    = fs.String("handover", "", "path to the handover_payload JSON file")
+		approvalKeysEnv = fs.String("approval-keys-env", "APPROVAL_SIGNER_KEYS", "env var listing approval signer keys as kid=base64(public)")
+	)
+	if err := fs.Parse(args); err != nil {
+		return err
+	}
+
+	cfg, err := loadConfig(*approvalKeysEnv)
+	if err != nil {
+		return err
+	}
+	if *workflowID == "" || *approvalRef == "" || *handoverPath == "" {
+		return errors.New("-workflow, -approval-ref, and -handover are required")
+	}
+	payload, err := loadHandoverPayload(*handoverPath)
+	if err != nil {
+		return err
+	}
+
+	runner := &transform.Runner{
+		Config: cfg.transformCfg,
+		Approvals: approval.Client{
+			BaseURL: cfg.tlogURL,
+		},
+		ApprovalKeyring: cfg.approvalKeyring,
+		Signer: signer.Client{
+			BaseURL:       cfg.signingURL,
+			PocketIDToken: cfg.pocketIDSource,
+			WorkloadToken: cfg.workloadSource,
+		},
+		TLog: tlog.Client{BaseURL: cfg.tlogURL},
+		Sink: sink.Client{BaseURL: cfg.sinkURL},
+		Now:  time.Now,
+	}
+
+	res, err := runner.Execute(ctx, transform.Request{
+		WorkflowID:      *workflowID,
+		ApprovalRef:     *approvalRef,
+		HandoverPayload: payload,
+	})
+	if err != nil {
+		return err
+	}
+	slog.Info("transform complete",
+		"workflow_id", *workflowID,
+		"approval_ref", *approvalRef,
+		"transform_ref", res.TransformRef,
+		"log_index", res.LogIndex,
+		"sink_status", res.SinkStatus,
+		"handover_sha256", res.HandoverHashHex,
+	)
+	fmt.Fprintln(os.Stdout, res.TransformRef)
+	return nil
+}
+
+type runtimeConfig struct {
+	tlogURL         string
+	signingURL      string
+	sinkURL         string
+	pocketIDSource  auth.TokenSource
+	workloadSource  auth.TokenSource
+	approvalKeyring dsse.Keyring
+	transformCfg    transform.Config
+}
+
+func loadConfig(keysEnv string) (runtimeConfig, error) {
+	var cfg runtimeConfig
+	cfg.tlogURL = envRequired("TRANSFORM_TLOG_URL")
+	cfg.signingURL = envRequired("TRANSFORM_SIGNING_URL")
+	cfg.sinkURL = envRequired("TRANSFORM_SINK_URL")
+
+	if cfg.tlogURL == "" || cfg.signingURL == "" || cfg.sinkURL == "" {
+		return cfg, errors.New("TRANSFORM_TLOG_URL, TRANSFORM_SIGNING_URL, TRANSFORM_SINK_URL are required")
+	}
+
+	issuer := envRequired("POCKET_ID_ISSUER")
+	clientID := envRequired("POCKET_ID_CLIENT_ID")
+	clientSecret := envRequired("POCKET_ID_CLIENT_SECRET")
+	if issuer == "" || clientID == "" || clientSecret == "" {
+		return cfg, errors.New("POCKET_ID_ISSUER, POCKET_ID_CLIENT_ID, POCKET_ID_CLIENT_SECRET are required")
+	}
+	cfg.pocketIDSource = &auth.PocketIDTokenSource{
+		Issuer:       issuer,
+		ClientID:     clientID,
+		ClientSecret: clientSecret,
+		Audience:     envDefault("POCKET_ID_AUDIENCE", "trust-api"),
+	}
+
+	saPath := envDefault("TRANSFORM_WORKLOAD_TOKEN_PATH", "/var/run/secrets/tokens/trust-api")
+	cfg.workloadSource = &auth.ProjectedSATokenSource{Path: saPath}
+
+	kr, err := loadKeyring(keysEnv)
+	if err != nil {
+		return cfg, err
+	}
+	if len(kr) == 0 {
+		return cfg, fmt.Errorf("%s must list at least one approval signer key", keysEnv)
+	}
+	cfg.approvalKeyring = kr
+
+	cfg.transformCfg = transform.Config{
+		Actor:             envDefault("TRANSFORM_ACTOR", "agent-testagent-transform"),
+		Operation:         envDefault("TRANSFORM_OPERATION", "expense.map_to_sink"),
+		SinkTarget:        envDefault("TRANSFORM_SINK_TARGET", "sink:dummy-sink"),
+		SigningKeyRef:     envDefault("TRANSFORM_SIGNING_KEY_REF", "trust-api/agent-testagent-transform-2026-q4"),
+		Input:             transform.SchemaRef{Name: envDefault("TRANSFORM_INPUT_SCHEMA", "expense.canonical"), Version: envDefault("TRANSFORM_INPUT_VERSION", "1.2.0")},
+		Output:            transform.SchemaRef{Name: envDefault("TRANSFORM_OUTPUT_SCHEMA", "sink.db.expense"), Version: envDefault("TRANSFORM_OUTPUT_VERSION", "1.2.0")},
+		TransformVersion:  envDefault("TRANSFORM_VERSION", "0.1.0"),
+		SinkPayloadSchema: envDefault("TRANSFORM_SINK_PAYLOAD_SCHEMA", "sink.dummy.v1"),
+	}
+	return cfg, nil
+}
+
+func loadHandoverPayload(path string) (map[string]any, error) {
+	raw, err := os.ReadFile(path)
+	if err != nil {
+		return nil, fmt.Errorf("read handover payload %q: %w", path, err)
+	}
+	var out map[string]any
+	if err := json.Unmarshal(raw, &out); err != nil {
+		return nil, fmt.Errorf("decode handover payload %q: %w", path, err)
+	}
+	return out, nil
+}
+
+func loadKeyring(envName string) (dsse.Keyring, error) {
+	raw := strings.TrimSpace(os.Getenv(envName))
+	if raw == "" {
+		return nil, nil
+	}
+	kr := dsse.Keyring{}
+	for _, entry := range strings.Split(raw, ",") {
+		entry = strings.TrimSpace(entry)
+		if entry == "" {
+			continue
+		}
+		eq := strings.IndexByte(entry, '=')
+		if eq <= 0 {
+			return nil, fmt.Errorf("%s: entry %q must be kid=base64(public-key)", envName, entry)
+		}
+		kid := entry[:eq]
+		pubEnc := entry[eq+1:]
+		pubRaw, err := decodePubKey(pubEnc)
+		if err != nil {
+			return nil, fmt.Errorf("%s: kid %q: %w", envName, kid, err)
+		}
+		if len(pubRaw) != ed25519.PublicKeySize {
+			return nil, fmt.Errorf("%s: kid %q: expected %d-byte ed25519 public key, got %d", envName, kid, ed25519.PublicKeySize, len(pubRaw))
+		}
+		kr[kid] = ed25519.PublicKey(pubRaw)
+	}
+	return kr, nil
+}
+
+// decodePubKey accepts base64url (no padding) or hex.
+func decodePubKey(s string) ([]byte, error) {
+	s = strings.TrimSpace(s)
+	if b, err := base64.RawURLEncoding.DecodeString(s); err == nil && len(b) == ed25519.PublicKeySize {
+		return b, nil
+	}
+	if b, err := base64.StdEncoding.DecodeString(s); err == nil && len(b) == ed25519.PublicKeySize {
+		return b, nil
+	}
+	if b, err := hex.DecodeString(s); err == nil && len(b) == ed25519.PublicKeySize {
+		return b, nil
+	}
+	return nil, errors.New("public key is not base64url/base64/hex of a 32-byte ed25519 key")
+}
+
+func envRequired(name string) string {
+	return strings.TrimSpace(os.Getenv(name))
+}
+
+func envDefault(name, def string) string {
+	v := strings.TrimSpace(os.Getenv(name))
+	if v == "" {
+		return def
+	}
+	return v
+}

services/testagent-transform/go.mod

@@ -0,0 +1,3 @@
+module basicstack.de/proofedmesh/services/testagent-transform
+
+go 1.23

services/testagent-transform/internal/approval/client.go

@@ -0,0 +1,119 @@
+// Package approval retrieves an approval attestation from the transparency
+// log by its content_hash (`attestation_ref`).
+//
+// The TLog's write path (POST /api/v1/log/entries) is defined in
+// docs/adr/0005-signing-service-and-transparency-log-api.md. The read path
+// is this agent's companion: GET /api/v1/log/entries/{content_hash}, which
+// returns the originally-submitted DSSE envelope plus its log metadata so
+// a downstream verifier can replay the signature check without trusting
+// the TLog's own storage of the plaintext.
+//
+// Phase-1 scope: the agent assumes the TLog exposes this GET endpoint.
+// For CI/dev the end-to-end test wires an httptest handler of the exact
+// same shape.
+package approval
+
+import (
+	"context"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"io"
+	"net/http"
+	"net/url"
+	"strings"
+	"time"
+
+	"basicstack.de/proofedmesh/services/testagent-transform/internal/auth"
+	"basicstack.de/proofedmesh/services/testagent-transform/internal/dsse"
+)
+
+// Entry is the response the testagent-transform expects from
+// GET /api/v1/log/entries/{content_hash}.
+type Entry struct {
+	ContentHash string        `json:"content_hash"`
+	Envelope    dsse.Envelope `json:"envelope"`
+	LogIndex    int64         `json:"log_index"`
+	LoggedAt    time.Time     `json:"logged_at"`
+}
+
+// ErrNotFound is returned on a 404 from the TLog read endpoint.
+var ErrNotFound = errors.New("approval: attestation_ref not in transparency-log")
+
+// ErrTLogUnavailable classifies connection errors and 5xx responses.
+var ErrTLogUnavailable = errors.New("approval: transparency-log unavailable")
+
+// Client is the TLog read client.
+type Client struct {
+	BaseURL     string
+	HTTPClient  *http.Client
+	TokenSource auth.TokenSource
+}
+
+// Fetch retrieves the DSSE envelope and log metadata for attestationRef.
+// attestationRef must be `sha256:<64 hex>` (the stable content_hash).
+func (c Client) Fetch(ctx context.Context, attestationRef string) (Entry, error) {
+	if c.BaseURL == "" {
+		return Entry{}, errors.New("approval.Client: BaseURL is empty")
+	}
+	ref := strings.TrimSpace(attestationRef)
+	if ref == "" {
+		return Entry{}, errors.New("approval.Client: attestation_ref is empty")
+	}
+	hc := c.HTTPClient
+	if hc == nil {
+		hc = &http.Client{Timeout: 10 * time.Second}
+	}
+	endpoint, err := url.JoinPath(c.BaseURL, "/api/v1/log/entries/", url.PathEscape(ref))
+	if err != nil {
+		return Entry{}, fmt.Errorf("approval: build url: %w", err)
+	}
+	req, err := http.NewRequestWithContext(ctx, http.MethodGet, endpoint, nil)
+	if err != nil {
+		return Entry{}, err
+	}
+	req.Header.Set("Accept", "application/json")
+	if c.TokenSource != nil {
+		tok, err := c.TokenSource.Token(ctx)
+		if err != nil {
+			return Entry{}, fmt.Errorf("approval token: %w", err)
+		}
+		if tok != "" {
+			req.Header.Set("Authorization", "Bearer "+tok)
+		}
+	}
+	resp, err := hc.Do(req)
+	if err != nil {
+		return Entry{}, fmt.Errorf("%w: %v", ErrTLogUnavailable, err)
+	}
+	defer resp.Body.Close()
+	raw, _ := io.ReadAll(io.LimitReader(resp.Body, 1<<20))
+	switch {
+	case resp.StatusCode == http.StatusOK:
+		// fall through
+	case resp.StatusCode == http.StatusNotFound:
+		return Entry{}, ErrNotFound
+	case resp.StatusCode >= 500:
+		return Entry{}, fmt.Errorf("%w: status %d: %s", ErrTLogUnavailable, resp.StatusCode, truncate(raw, 256))
+	default:
+		return Entry{}, fmt.Errorf("approval: status %d: %s", resp.StatusCode, truncate(raw, 256))
+	}
+	var out Entry
+	if err := json.Unmarshal(raw, &out); err != nil {
+		return Entry{}, fmt.Errorf("approval: decode response: %w", err)
+	}
+	if out.ContentHash == "" {
+		return Entry{}, errors.New("approval: response missing content_hash")
+	}
+	if out.ContentHash != ref {
+		return Entry{}, fmt.Errorf("approval: TLog returned content_hash %q != requested %q", out.ContentHash, ref)
+	}
+	return out, nil
+}
+
+func truncate(b []byte, n int) string {
+	if len(b) <= n {
+		return string(b)
+	}
+	return string(b[:n]) + "…"
+}

services/testagent-transform/internal/approval/client_test.go

@@ -0,0 +1,84 @@
+package approval
+
+import (
+	"context"
+	"encoding/json"
+	"errors"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+	"time"
+
+	"basicstack.de/proofedmesh/services/testagent-transform/internal/dsse"
+)
+
+func TestFetch_HappyPath(t *testing.T) {
+	ref := "sha256:" + "aa" + stringRepeat("b", 62)
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		if r.URL.Path != "/api/v1/log/entries/"+ref {
+			http.NotFound(w, r)
+			return
+		}
+		w.Header().Set("Content-Type", "application/json")
+		_ = json.NewEncoder(w).Encode(Entry{
+			ContentHash: ref,
+			Envelope:    dsse.Envelope{PayloadType: "x", Payload: "aGk"},
+			LogIndex:    99,
+			LoggedAt:    time.Now(),
+		})
+	}))
+	defer srv.Close()
+	c := Client{BaseURL: srv.URL}
+	e, err := c.Fetch(context.Background(), ref)
+	if err != nil {
+		t.Fatalf("Fetch: %v", err)
+	}
+	if e.LogIndex != 99 || e.ContentHash != ref {
+		t.Fatalf("entry = %+v", e)
+	}
+}
+
+func TestFetch_404MapsToNotFound(t *testing.T) {
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, _ *http.Request) {
+		http.NotFound(w, nil)
+	}))
+	defer srv.Close()
+	c := Client{BaseURL: srv.URL}
+	_, err := c.Fetch(context.Background(), "sha256:x")
+	if !errors.Is(err, ErrNotFound) {
+		t.Fatalf("want ErrNotFound, got %v", err)
+	}
+}
+
+func TestFetch_5xxMapsToUnavailable(t *testing.T) {
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, _ *http.Request) {
+		http.Error(w, "boom", http.StatusInternalServerError)
+	}))
+	defer srv.Close()
+	c := Client{BaseURL: srv.URL}
+	_, err := c.Fetch(context.Background(), "sha256:x")
+	if !errors.Is(err, ErrTLogUnavailable) {
+		t.Fatalf("want ErrTLogUnavailable, got %v", err)
+	}
+}
+
+func TestFetch_ContentHashMismatchIsReported(t *testing.T) {
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, _ *http.Request) {
+		w.Header().Set("Content-Type", "application/json")
+		_ = json.NewEncoder(w).Encode(Entry{ContentHash: "sha256:other", Envelope: dsse.Envelope{}})
+	}))
+	defer srv.Close()
+	c := Client{BaseURL: srv.URL}
+	_, err := c.Fetch(context.Background(), "sha256:expected")
+	if err == nil {
+		t.Fatal("expected error on content_hash mismatch")
+	}
+}
+
+func stringRepeat(s string, n int) string {
+	out := make([]byte, 0, len(s)*n)
+	for i := 0; i < n; i++ {
+		out = append(out, s...)
+	}
+	return string(out)
+}

services/testagent-transform/internal/auth/pocket_id.go

@@ -0,0 +1,178 @@
+package auth
+
+import (
+	"context"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"io"
+	"net/http"
+	"net/url"
+	"strings"
+	"sync"
+	"time"
+)
+
+// PocketIDTokenSource issues Bearer tokens using the Pocket-ID OIDC
+// `client_credentials` grant and caches each token until shortly before its
+// expiry. Safe for concurrent use.
+//
+// Mirrors services/admin-api/internal/attest/pocket_id_token_source.go in
+// shape so the signing-service's Pocket-ID validator sees the same token
+// format admin-api and approval-service already send.
+type PocketIDTokenSource struct {
+	// Issuer is the Pocket-ID base URL, e.g. "https://auth.basicstack.de".
+	// Trailing slash optional.
+	Issuer string
+	// ClientID / ClientSecret identify the testagent-transform's Pocket-ID
+	// OIDC client. Sourced from env (POCKET_ID_CLIENT_ID /
+	// POCKET_ID_CLIENT_SECRET) in production so they do not land in
+	// process listings.
+	ClientID     string
+	ClientSecret string
+	// Scope / Audience are optional OIDC parameters; empty when the
+	// server-side policy does not require them.
+	Scope    string
+	Audience string
+	// Client overrides the default HTTP client. Default: 10s timeout.
+	Client *http.Client
+	// RefreshLeeway is the window before token expiry at which the cache
+	// is considered invalid. Zero defaults to 30s.
+	RefreshLeeway time.Duration
+	// Now is injected for deterministic tests. Zero defaults to time.Now.
+	Now func() time.Time
+
+	mu            sync.Mutex
+	tokenEndpoint string
+	cachedToken   string
+	cachedExpiry  time.Time
+}
+
+type pocketIDTokenResponse struct {
+	AccessToken string `json:"access_token"`
+	TokenType   string `json:"token_type"`
+	ExpiresIn   int    `json:"expires_in"`
+}
+
+type pocketIDDiscoveryDoc struct {
+	TokenEndpoint string `json:"token_endpoint"`
+}
+
+// Token returns a cached access token when still valid, or fetches a fresh
+// one from Pocket-ID.
+func (p *PocketIDTokenSource) Token(ctx context.Context) (string, error) {
+	if p == nil {
+		return "", errors.New("auth.PocketIDTokenSource: nil receiver")
+	}
+	if p.Issuer == "" {
+		return "", errors.New("auth.PocketIDTokenSource: Issuer is required")
+	}
+	if p.ClientID == "" || p.ClientSecret == "" {
+		return "", errors.New("auth.PocketIDTokenSource: ClientID and ClientSecret are required")
+	}
+
+	p.mu.Lock()
+	defer p.mu.Unlock()
+
+	leeway := p.RefreshLeeway
+	if leeway <= 0 {
+		leeway = 30 * time.Second
+	}
+	now := p.nowLocked()
+	if p.cachedToken != "" && now.Add(leeway).Before(p.cachedExpiry) {
+		return p.cachedToken, nil
+	}
+
+	if p.tokenEndpoint == "" {
+		if err := p.discoverLocked(ctx); err != nil {
+			return "", err
+		}
+	}
+
+	tok, expiry, err := p.fetchLocked(ctx, now)
+	if err != nil {
+		return "", err
+	}
+	p.cachedToken = tok
+	p.cachedExpiry = expiry
+	return tok, nil
+}
+
+func (p *PocketIDTokenSource) nowLocked() time.Time {
+	if p.Now != nil {
+		return p.Now()
+	}
+	return time.Now()
+}
+
+func (p *PocketIDTokenSource) httpClient() *http.Client {
+	if p.Client != nil {
+		return p.Client
+	}
+	return &http.Client{Timeout: 10 * time.Second}
+}
+
+func (p *PocketIDTokenSource) discoverLocked(ctx context.Context) error {
+	base := strings.TrimRight(p.Issuer, "/")
+	req, err := http.NewRequestWithContext(ctx, http.MethodGet, base+"/.well-known/openid-configuration", nil)
+	if err != nil {
+		return fmt.Errorf("pocket id discovery: %w", err)
+	}
+	req.Header.Set("Accept", "application/json")
+	resp, err := p.httpClient().Do(req)
+	if err != nil {
+		return fmt.Errorf("pocket id discovery: %w", err)
+	}
+	defer resp.Body.Close()
+	raw, _ := io.ReadAll(io.LimitReader(resp.Body, 1<<20))
+	if resp.StatusCode != http.StatusOK {
+		return fmt.Errorf("pocket id discovery: status %d: %s", resp.StatusCode, string(raw))
+	}
+	var doc pocketIDDiscoveryDoc
+	if err := json.Unmarshal(raw, &doc); err != nil {
+		return fmt.Errorf("pocket id discovery: decode: %w", err)
+	}
+	if doc.TokenEndpoint == "" {
+		return errors.New("pocket id discovery: token_endpoint missing from OIDC configuration")
+	}
+	p.tokenEndpoint = doc.TokenEndpoint
+	return nil
+}
+
+func (p *PocketIDTokenSource) fetchLocked(ctx context.Context, now time.Time) (string, time.Time, error) {
+	form := url.Values{}
+	form.Set("grant_type", "client_credentials")
+	if p.Scope != "" {
+		form.Set("scope", p.Scope)
+	}
+	if p.Audience != "" {
+		form.Set("audience", p.Audience)
+	}
+	req, err := http.NewRequestWithContext(ctx, http.MethodPost, p.tokenEndpoint, strings.NewReader(form.Encode()))
+	if err != nil {
+		return "", time.Time{}, fmt.Errorf("pocket id token: %w", err)
+	}
+	req.SetBasicAuth(p.ClientID, p.ClientSecret)
+	req.Header.Set("Content-Type", "application/x-www-form-urlencoded")
+	req.Header.Set("Accept", "application/json")
+	resp, err := p.httpClient().Do(req)
+	if err != nil {
+		return "", time.Time{}, fmt.Errorf("pocket id token: %w", err)
+	}
+	defer resp.Body.Close()
+	raw, _ := io.ReadAll(io.LimitReader(resp.Body, 1<<20))
+	if resp.StatusCode != http.StatusOK {
+		return "", time.Time{}, fmt.Errorf("pocket id token: status %d: %s", resp.StatusCode, string(raw))
+	}
+	var out pocketIDTokenResponse
+	if err := json.Unmarshal(raw, &out); err != nil {
+		return "", time.Time{}, fmt.Errorf("pocket id token: decode: %w", err)
+	}
+	if out.AccessToken == "" {
+		return "", time.Time{}, errors.New("pocket id token: response missing access_token")
+	}
+	if out.ExpiresIn <= 0 {
+		return "", time.Time{}, errors.New("pocket id token: response has non-positive expires_in")
+	}
+	return out.AccessToken, now.Add(time.Duration(out.ExpiresIn) * time.Second), nil
+}

services/testagent-transform/internal/auth/sa_token.go

@@ -0,0 +1,80 @@
+package auth
+
+import (
+	"context"
+	"fmt"
+	"os"
+	"strings"
+	"sync"
+	"time"
+)
+
+// ProjectedSATokenSource reads the kubelet-written projected
+// ServiceAccount token from a mounted Volume (typically
+// `/var/run/secrets/tokens/trust-api`) and re-reads it on each call so
+// kubelet's periodic refresh is picked up without a service restart.
+//
+// A short in-process cache avoids a syscall on every signing-service call;
+// kubelet refreshes projected tokens well before their `exp`, so a few
+// seconds of staleness is fine. The cache is bypassed by setting
+// CacheTTL <= 0.
+type ProjectedSATokenSource struct {
+	// Path is the absolute path to the projected token file. Required.
+	// The Volume is typically defined with:
+	//   projected:
+	//     sources:
+	//     - serviceAccountToken:
+	//         path: trust-api
+	//         audience: trust-api
+	//         expirationSeconds: 3600
+	Path string
+	// CacheTTL bounds how long an already-read token value is reused
+	// without re-reading the file. Zero defaults to 30 seconds. Negative
+	// disables caching.
+	CacheTTL time.Duration
+	// Now is injected for deterministic tests. Zero defaults to time.Now.
+	Now func() time.Time
+
+	mu          sync.Mutex
+	cachedToken string
+	cachedAt    time.Time
+}
+
+// Token returns the current projected ServiceAccount token.
+func (p *ProjectedSATokenSource) Token(_ context.Context) (string, error) {
+	if p == nil {
+		return "", fmt.Errorf("auth.ProjectedSATokenSource: nil receiver")
+	}
+	if p.Path == "" {
+		return "", fmt.Errorf("auth.ProjectedSATokenSource: Path is required")
+	}
+	p.mu.Lock()
+	defer p.mu.Unlock()
+
+	ttl := p.CacheTTL
+	if ttl == 0 {
+		ttl = 30 * time.Second
+	}
+	now := p.now()
+	if ttl > 0 && p.cachedToken != "" && now.Sub(p.cachedAt) < ttl {
+		return p.cachedToken, nil
+	}
+	raw, err := os.ReadFile(p.Path)
+	if err != nil {
+		return "", fmt.Errorf("read projected SA token %q: %w", p.Path, err)
+	}
+	tok := strings.TrimSpace(string(raw))
+	if tok == "" {
+		return "", fmt.Errorf("projected SA token at %q is empty", p.Path)
+	}
+	p.cachedToken = tok
+	p.cachedAt = now
+	return tok, nil
+}
+
+func (p *ProjectedSATokenSource) now() time.Time {
+	if p.Now != nil {
+		return p.Now()
+	}
+	return time.Now()
+}

services/testagent-transform/internal/auth/sa_token_test.go

@@ -0,0 +1,84 @@
+package auth
+
+import (
+	"context"
+	"os"
+	"path/filepath"
+	"testing"
+	"time"
+)
+
+func TestProjectedSATokenSource_ReadsTokenFromFile(t *testing.T) {
+	dir := t.TempDir()
+	path := filepath.Join(dir, "trust-api")
+	if err := os.WriteFile(path, []byte("tok-abc\n"), 0o600); err != nil {
+		t.Fatal(err)
+	}
+	src := &ProjectedSATokenSource{Path: path}
+	tok, err := src.Token(context.Background())
+	if err != nil {
+		t.Fatal(err)
+	}
+	if tok != "tok-abc" {
+		t.Fatalf("tok = %q", tok)
+	}
+}
+
+func TestProjectedSATokenSource_CachesWithinTTL(t *testing.T) {
+	dir := t.TempDir()
+	path := filepath.Join(dir, "trust-api")
+	if err := os.WriteFile(path, []byte("v1"), 0o600); err != nil {
+		t.Fatal(err)
+	}
+	start := time.Date(2026, 10, 25, 20, 0, 0, 0, time.UTC)
+	nowOffset := time.Duration(0)
+	src := &ProjectedSATokenSource{
+		Path:     path,
+		CacheTTL: time.Second,
+		Now:      func() time.Time { return start.Add(nowOffset) },
+	}
+	first, err := src.Token(context.Background())
+	if err != nil {
+		t.Fatal(err)
+	}
+	// Overwrite the file; cache should hide the new value.
+	if err := os.WriteFile(path, []byte("v2"), 0o600); err != nil {
+		t.Fatal(err)
+	}
+	nowOffset = 500 * time.Millisecond
+	second, err := src.Token(context.Background())
+	if err != nil {
+		t.Fatal(err)
+	}
+	if first != "v1" || second != "v1" {
+		t.Fatalf("cache missed: first=%q second=%q", first, second)
+	}
+	// Past TTL: must re-read.
+	nowOffset = 2 * time.Second
+	third, err := src.Token(context.Background())
+	if err != nil {
+		t.Fatal(err)
+	}
+	if third != "v2" {
+		t.Fatalf("expected v2 after TTL expiry, got %q", third)
+	}
+}
+
+func TestProjectedSATokenSource_EmptyFile(t *testing.T) {
+	dir := t.TempDir()
+	path := filepath.Join(dir, "trust-api")
+	if err := os.WriteFile(path, []byte("   \n"), 0o600); err != nil {
+		t.Fatal(err)
+	}
+	src := &ProjectedSATokenSource{Path: path}
+	if _, err := src.Token(context.Background()); err == nil {
+		t.Fatal("expected error on empty token")
+	}
+}
+
+func TestProjectedSATokenSource_MissingFile(t *testing.T) {
+	src := &ProjectedSATokenSource{Path: "/nonexistent/trust-api"}
+	if _, err := src.Token(context.Background()); err == nil {
+		t.Fatal("expected error on missing token file")
+	}
+}

services/testagent-transform/internal/auth/token_source.go

@@ -0,0 +1,30 @@
+// Package auth exposes the two identity sources the testagent-transform
+// uses to call the signing-service:
+//
+//  1. Pocket-ID client_credentials access token (Authorization: Bearer …)
+//  2. Projected ServiceAccount token (X-Workload-Token …) read from a
+//     kubelet-managed Volume (`projected: { serviceAccountToken: … }`).
+//
+// Both are modelled as the same TokenSource interface so the orchestration
+// code never cares about the identity's origin.
+package auth
+
+import "context"
+
+// TokenSource returns a bearer-style token. The caller is expected to
+// retry on error; implementations may cache internally.
+type TokenSource interface {
+	Token(ctx context.Context) (string, error)
+}
+
+// StaticToken is a constant TokenSource. Primarily used in tests.
+type StaticToken string
+
+// Token returns s.
+func (s StaticToken) Token(_ context.Context) (string, error) { return string(s), nil }
+
+// TokenFunc adapts a plain function to TokenSource.
+type TokenFunc func(ctx context.Context) (string, error)
+
+// Token calls f.
+func (f TokenFunc) Token(ctx context.Context) (string, error) { return f(ctx) }

services/testagent-transform/internal/canonical/canonical.go

@@ -0,0 +1,102 @@
+// Package canonical implements the deterministic JSON serialisation the
+// testagent-transform uses to compute the handover_payload content hash.
+//
+// MUST stay byte-for-byte compatible with
+// services/approval-service/internal/canonical/canonical.go and
+// services/signing-service/internal/canonical/canonical.go so a subject
+// digest signed here reproduces identically on the verifier side.
+package canonical
+
+import (
+	"bytes"
+	"crypto/sha256"
+	"encoding/hex"
+	"encoding/json"
+	"fmt"
+	"sort"
+)
+
+// SHA256Hex returns the hex-encoded SHA-256 of b.
+func SHA256Hex(b []byte) string {
+	sum := sha256.Sum256(b)
+	return hex.EncodeToString(sum[:])
+}
+
+// Marshal returns the canonical JSON encoding of v (sorted object keys).
+func Marshal(v any) ([]byte, error) {
+	first, err := json.Marshal(v)
+	if err != nil {
+		return nil, err
+	}
+	var any_ any
+	if err := json.Unmarshal(first, &any_); err != nil {
+		return nil, err
+	}
+	var buf bytes.Buffer
+	if err := writeSorted(&buf, any_); err != nil {
+		return nil, err
+	}
+	return buf.Bytes(), nil
+}
+
+// Hash returns the sha256:<hex> content hash of v's canonical JSON along
+// with the raw canonical bytes.
+func Hash(v any) (string, []byte, error) {
+	raw, err := Marshal(v)
+	if err != nil {
+		return "", nil, err
+	}
+	return "sha256:" + SHA256Hex(raw), raw, nil
+}
+
+func writeSorted(buf *bytes.Buffer, v any) error {
+	switch x := v.(type) {
+	case nil:
+		buf.WriteString("null")
+	case bool:
+		if x {
+			buf.WriteString("true")
+		} else {
+			buf.WriteString("false")
+		}
+	case float64:
+		b, _ := json.Marshal(x)
+		buf.Write(b)
+	case string:
+		b, _ := json.Marshal(x)
+		buf.Write(b)
+	case []any:
+		buf.WriteByte('[')
+		for i, el := range x {
+			if i > 0 {
+				buf.WriteByte(',')
+			}
+			if err := writeSorted(buf, el); err != nil {
+				return err
+			}
+		}
+		buf.WriteByte(']')
+	case map[string]any:
+		keys := make([]string, 0, len(x))
+		for k := range x {
+			keys = append(keys, k)
+		}
+		sort.Strings(keys)
+		buf.WriteByte('{')
+		for i, k := range keys {
+			if i > 0 {
+				buf.WriteByte(',')
+			}
+			kb, _ := json.Marshal(k)
+			buf.Write(kb)
+			buf.WriteByte(':')
+			if err := writeSorted(buf, x[k]); err != nil {
+				return err
+			}
+		}
+		buf.WriteByte('}')
+	default:
+		return fmt.Errorf("canonical.writeSorted: unsupported type %T", v)
+	}
+	return nil
+}

services/testagent-transform/internal/dsse/dsse.go

@@ -0,0 +1,99 @@
+// Package dsse models the DSSE envelope shape the signing-service produces
+// and verifies an envelope's Ed25519 signature using the DSSEv1 Pre-
+// Authentication Encoding (PAE) from the DSSE spec.
+//
+// The envelope shape mirrors
+// services/approval-service/internal/signer.Envelope so an approval fetched
+// from the transparency-log round-trips through this package byte-for-byte.
+package dsse
+
+import (
+	"crypto/ed25519"
+	"encoding/base64"
+	"errors"
+	"fmt"
+)
+
+// EnvelopeSignature mirrors the DSSE spec.
+type EnvelopeSignature struct {
+	KeyID string `json:"keyid"`
+	Sig   string `json:"sig"`
+}
+
+// Envelope is the DSSE envelope the signing-service returns. Payload is
+// base64url (no padding) of the canonical in-toto Statement bytes.
+type Envelope struct {
+	PayloadType string              `json:"payloadType"`
+	Payload     string              `json:"payload"`
+	Signatures  []EnvelopeSignature `json:"signatures"`
+}
+
+// Keyring maps keyid (as embedded in the envelope signature) to the
+// Ed25519 public key that signed it. The testagent-transform ships a
+// pinned keyring for the approval-signer key; a Phase-2 verifier would
+// pull the key material from the Agent Registry (`agent_keys` table).
+type Keyring map[string]ed25519.PublicKey
+
+// ErrNoSignatures is returned when the envelope has no signatures to try.
+var ErrNoSignatures = errors.New("dsse: envelope has no signatures")
+
+// ErrUnknownKey is returned when none of the envelope's signatures has a
+// keyid that is present in the verifier's keyring.
+var ErrUnknownKey = errors.New("dsse: no signature keyid is in the keyring")
+
+// ErrSignatureInvalid is returned when at least one keyring-matching
+// signature was tried and none verified.
+var ErrSignatureInvalid = errors.New("dsse: no signature verified against its keyring entry")
+
+// Verify checks that at least one signature on env matches a public key in
+// kr. The payload is base64url-decoded, the DSSEv1 PAE is reconstructed,
+// and ed25519.Verify is applied. On success the decoded payload bytes are
+// returned so the caller can parse the in-toto Statement.
+//
+// Returns ErrUnknownKey when the envelope has signatures but none list a
+// keyid that is in the keyring (so no verification was even attempted),
+// and ErrSignatureInvalid when attempts ran but all failed.
+func Verify(env Envelope, kr Keyring) ([]byte, error) {
+	if len(env.Signatures) == 0 {
+		return nil, ErrNoSignatures
+	}
+	payload, err := base64.RawURLEncoding.DecodeString(env.Payload)
+	if err != nil {
+		return nil, fmt.Errorf("dsse: decode payload: %w", err)
+	}
+	pae := pae(env.PayloadType, payload)
+
+	tried := false
+	for _, sig := range env.Signatures {
+		pub, ok := kr[sig.KeyID]
+		if !ok {
+			continue
+		}
+		tried = true
+		raw, err := base64.RawURLEncoding.DecodeString(sig.Sig)
+		if err != nil {
+			continue
+		}
+		if ed25519.Verify(pub, pae, raw) {
+			return payload, nil
+		}
+	}
+	if !tried {
+		return nil, ErrUnknownKey
+	}
+	return nil, ErrSignatureInvalid
+}
+
+// pae reconstructs the DSSEv1 Pre-Authentication Encoding:
+//
+//	"DSSEv1 " || len(payloadType) || " " || payloadType || " " || len(payload) || " " || payload
+//
+// (ASCII decimal lengths, bytes.) See
+// https://github.com/secure-systems-lab/dsse/blob/master/protocol.md.
+func pae(payloadType string, payload []byte) []byte {
+	prefix := fmt.Sprintf("DSSEv1 %d %s %d ", len(payloadType), payloadType, len(payload))
+	out := make([]byte, 0, len(prefix)+len(payload))
+	out = append(out, prefix...)
+	out = append(out, payload...)
+	return out
+}

services/testagent-transform/internal/dsse/dsse_test.go

@@ -0,0 +1,70 @@
+package dsse
+
+import (
+	"crypto/ed25519"
+	"crypto/rand"
+	"encoding/base64"
+	"errors"
+	"fmt"
+	"testing"
+)
+
+func TestVerify_HappyPath(t *testing.T) {
+	pub, priv, err := ed25519.GenerateKey(rand.Reader)
+	if err != nil {
+		t.Fatal(err)
+	}
+	payload := []byte(`{"hello":"world"}`)
+	env := signEnv(t, "application/vnd.in-toto+json", payload, "k1", priv)
+	got, err := Verify(env, Keyring{"k1": pub})
+	if err != nil {
+		t.Fatalf("Verify: %v", err)
+	}
+	if string(got) != string(payload) {
+		t.Fatalf("payload = %q", got)
+	}
+}
+
+func TestVerify_UnknownKeyID(t *testing.T) {
+	_, priv, _ := ed25519.GenerateKey(rand.Reader)
+	otherPub, _, _ := ed25519.GenerateKey(rand.Reader)
+	env := signEnv(t, "x", []byte("hi"), "k1", priv)
+	_, err := Verify(env, Keyring{"other-kid": otherPub})
+	if !errors.Is(err, ErrUnknownKey) {
+		t.Fatalf("want ErrUnknownKey, got %v", err)
+	}
+}
+
+func TestVerify_SignatureInvalid(t *testing.T) {
+	pub, _, _ := ed25519.GenerateKey(rand.Reader)
+	// Build an envelope whose signature was made by a DIFFERENT private
+	// key but is listed under the keyring's keyid.
+	_, otherPriv, _ := ed25519.GenerateKey(rand.Reader)
+	env := signEnv(t, "x", []byte("hi"), "k1", otherPriv)
+	_, err := Verify(env, Keyring{"k1": pub})
+	if !errors.Is(err, ErrSignatureInvalid) {
+		t.Fatalf("want ErrSignatureInvalid, got %v", err)
+	}
+}
+
+func TestVerify_NoSignatures(t *testing.T) {
+	_, err := Verify(Envelope{PayloadType: "x", Payload: base64.RawURLEncoding.EncodeToString([]byte("hi"))}, Keyring{})
+	if !errors.Is(err, ErrNoSignatures) {
+		t.Fatalf("want ErrNoSignatures, got %v", err)
+	}
+}
+
+func signEnv(t *testing.T, payloadType string, payload []byte, keyID string, priv ed25519.PrivateKey) Envelope {
+	t.Helper()
+	pae := []byte(fmt.Sprintf("DSSEv1 %d %s %d ", len(payloadType), payloadType, len(payload)))
+	pae = append(pae, payload...)
+	sig := ed25519.Sign(priv, pae)
+	return Envelope{
+		PayloadType: payloadType,
+		Payload:     base64.RawURLEncoding.EncodeToString(payload),
+		Signatures: []EnvelopeSignature{{
+			KeyID: keyID,
+			Sig:   base64.RawURLEncoding.EncodeToString(sig),
+		}},
+	}
+}

services/testagent-transform/internal/signer/client.go

@@ -0,0 +1,150 @@
+// Package signer calls the signing-service's POST /api/v1/sign/dsse per
+// ADR-0005 using the double-identity flow:
+//
+//   - Authorization: Bearer <pocket-id-access-token>  (OIDC client identity)
+//   - X-Workload-Token: <projected-sa-token>          (K8s workload identity)
+//
+// The signing-service's structured policy evaluates BOTH identities against
+// the Agent Registry and the OPA policy — a Pocket-ID identity alone is not
+// enough to sign a transform statement in prod. See
+// services/signing-service/internal/httpapi/sign.go#useStructuredPath.
+package signer
+
+import (
+	"bytes"
+	"context"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"io"
+	"net/http"
+	"net/url"
+	"time"
+
+	"basicstack.de/proofedmesh/services/testagent-transform/internal/auth"
+	"basicstack.de/proofedmesh/services/testagent-transform/internal/dsse"
+)
+
+// WorkloadTokenHeader is the HTTP header carrying the projected
+// ServiceAccount token. Kept in sync with
+// services/signing-service/internal/token.WorkloadTokenHeader; duplicated
+// here so this module stays independent.
+const WorkloadTokenHeader = "X-Workload-Token"
+
+// Statement is the in-toto v1 Statement handed to the signing-service.
+// Loose typing lets arbitrary predicate payloads flow through without a
+// client-side schema registry; the signing-service validates the required
+// fields.
+type Statement map[string]any
+
+// SignedResult pairs the returned DSSE envelope with its content_hash.
+// content_hash is the stable attestation ID that the transparency-log is
+// addressed by.
+type SignedResult struct {
+	Envelope    dsse.Envelope `json:"envelope"`
+	ContentHash string        `json:"content_hash"`
+	SignedAt    time.Time     `json:"signed_at"`
+}
+
+// ErrSignerUnavailable is returned on connection errors or 5xx responses.
+var ErrSignerUnavailable = errors.New("signer: signing-service unavailable")
+
+// ErrSigningDenied is returned on 403 (OPA / registry mismatch). The
+// transform agent surfaces this to the caller — it is NOT retryable with
+// the same identities.
+var ErrSigningDenied = errors.New("signer: signing-service denied the request")
+
+// Client is the DSSE sign client.
+type Client struct {
+	BaseURL        string
+	HTTPClient     *http.Client
+	PocketIDToken  auth.TokenSource // Authorization: Bearer …
+	WorkloadToken  auth.TokenSource // X-Workload-Token: …
+}
+
+type signRequest struct {
+	KeyRef    string    `json:"key_ref"`
+	Statement Statement `json:"statement"`
+}
+
+// Sign calls POST /api/v1/sign/dsse. The signing-service returns a DSSE
+// envelope plus the stable content_hash of the envelope.
+func (c Client) Sign(ctx context.Context, keyRef string, stmt Statement) (SignedResult, error) {
+	if c.BaseURL == "" {
+		return SignedResult{}, errors.New("signer.Client: BaseURL is empty")
+	}
+	if c.PocketIDToken == nil {
+		return SignedResult{}, errors.New("signer.Client: PocketIDToken is required")
+	}
+	if c.WorkloadToken == nil {
+		return SignedResult{}, errors.New("signer.Client: WorkloadToken is required")
+	}
+	hc := c.HTTPClient
+	if hc == nil {
+		hc = &http.Client{Timeout: 10 * time.Second}
+	}
+	body, err := json.Marshal(signRequest{KeyRef: keyRef, Statement: stmt})
+	if err != nil {
+		return SignedResult{}, fmt.Errorf("signer: marshal request: %w", err)
+	}
+	endpoint, err := url.JoinPath(c.BaseURL, "/api/v1/sign/dsse")
+	if err != nil {
+		return SignedResult{}, fmt.Errorf("signer: build url: %w", err)
+	}
+	req, err := http.NewRequestWithContext(ctx, http.MethodPost, endpoint, bytes.NewReader(body))
+	if err != nil {
+		return SignedResult{}, err
+	}
+	req.Header.Set("Content-Type", "application/json")
+	req.Header.Set("Accept", "application/json")
+
+	pTok, err := c.PocketIDToken.Token(ctx)
+	if err != nil {
+		return SignedResult{}, fmt.Errorf("signer: pocket-id token: %w", err)
+	}
+	if pTok == "" {
+		return SignedResult{}, errors.New("signer: pocket-id token is empty")
+	}
+	req.Header.Set("Authorization", "Bearer "+pTok)
+
+	wTok, err := c.WorkloadToken.Token(ctx)
+	if err != nil {
+		return SignedResult{}, fmt.Errorf("signer: workload token: %w", err)
+	}
+	if wTok == "" {
+		return SignedResult{}, errors.New("signer: workload token is empty")
+	}
+	req.Header.Set(WorkloadTokenHeader, wTok)
+
+	resp, err := hc.Do(req)
+	if err != nil {
+		return SignedResult{}, fmt.Errorf("%w: %v", ErrSignerUnavailable, err)
+	}
+	defer resp.Body.Close()
+	raw, _ := io.ReadAll(io.LimitReader(resp.Body, 1<<20))
+	switch {
+	case resp.StatusCode == http.StatusOK:
+		// fall through
+	case resp.StatusCode == http.StatusForbidden:
+		return SignedResult{}, fmt.Errorf("%w: %s", ErrSigningDenied, truncate(raw, 256))
+	case resp.StatusCode >= 500:
+		return SignedResult{}, fmt.Errorf("%w: status %d: %s", ErrSignerUnavailable, resp.StatusCode, truncate(raw, 256))
+	default:
+		return SignedResult{}, fmt.Errorf("signer: status %d: %s", resp.StatusCode, truncate(raw, 256))
+	}
+	var out SignedResult
+	if err := json.Unmarshal(raw, &out); err != nil {
+		return SignedResult{}, fmt.Errorf("signer: decode response: %w", err)
+	}
+	if out.ContentHash == "" {
+		return SignedResult{}, errors.New("signer: response missing content_hash")
+	}
+	return out, nil
+}
+
+func truncate(b []byte, n int) string {
+	if len(b) <= n {
+		return string(b)
+	}
+	return string(b[:n]) + "…"
+}

services/testagent-transform/internal/signer/client_test.go

@@ -0,0 +1,120 @@
+package signer
+
+import (
+	"context"
+	"encoding/json"
+	"errors"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+	"time"
+
+	"basicstack.de/proofedmesh/services/testagent-transform/internal/auth"
+	"basicstack.de/proofedmesh/services/testagent-transform/internal/dsse"
+)
+
+const (
+	testBearer   = "pocket-id-bearer-xyz"
+	testWorkload = "wl-tok"
+)
+
+func TestSign_SendsBothIdentities(t *testing.T) {
+	seen := struct {
+		auth     string
+		workload string
+		keyRef   string
+	}{}
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		seen.auth = r.Header.Get("Authorization")
+		seen.workload = r.Header.Get(WorkloadTokenHeader)
+		var body struct {
+			KeyRef string `json:"key_ref"`
+		}
+		_ = json.NewDecoder(r.Body).Decode(&body)
+		seen.keyRef = body.KeyRef
+		resp := SignedResult{
+			Envelope:    dsse.Envelope{PayloadType: "application/vnd.in-toto+json", Payload: "aGk"},
+			ContentHash: "sha256:deadbeef",
+			SignedAt:    time.Now(),
+		}
+		w.Header().Set("Content-Type", "application/json")
+		_ = json.NewEncoder(w).Encode(resp)
+	}))
+	defer srv.Close()
+
+	c := Client{
+		BaseURL:       srv.URL,
+		PocketIDToken: auth.StaticToken(testBearer),
+		WorkloadToken: auth.StaticToken(testWorkload),
+	}
+	res, err := c.Sign(context.Background(), "key-x", Statement{"_type": "x"})
+	if err != nil {
+		t.Fatalf("Sign: %v", err)
+	}
+	if res.ContentHash != "sha256:deadbeef" {
+		t.Fatalf("ContentHash = %q", res.ContentHash)
+	}
+	if seen.auth != "Bearer "+testBearer {
+		t.Fatalf("Authorization = %q", seen.auth)
+	}
+	if seen.workload != testWorkload {
+		t.Fatalf("X-Workload-Token = %q", seen.workload)
+	}
+	if seen.keyRef != "key-x" {
+		t.Fatalf("key_ref = %q", seen.keyRef)
+	}
+}
+
+func TestSign_403MapsToSigningDenied(t *testing.T) {
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, _ *http.Request) {
+		w.WriteHeader(http.StatusForbidden)
+		_, _ = w.Write([]byte(`{"error":{"code":"signing_denied","message":"nope"}}`))
+	}))
+	defer srv.Close()
+	c := Client{BaseURL: srv.URL, PocketIDToken: auth.StaticToken("a"), WorkloadToken: auth.StaticToken("b")}
+	_, err := c.Sign(context.Background(), "k", Statement{"_type": "x"})
+	if !errors.Is(err, ErrSigningDenied) {
+		t.Fatalf("want ErrSigningDenied, got %v", err)
+	}
+}
+
+func TestSign_5xxMapsToUnavailable(t *testing.T) {
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, _ *http.Request) {
+		http.Error(w, "boom", http.StatusInternalServerError)
+	}))
+	defer srv.Close()
+	c := Client{BaseURL: srv.URL, PocketIDToken: auth.StaticToken("a"), WorkloadToken: auth.StaticToken("b")}
+	_, err := c.Sign(context.Background(), "k", Statement{"_type": "x"})
+	if !errors.Is(err, ErrSignerUnavailable) {
+		t.Fatalf("want ErrSignerUnavailable, got %v", err)
+	}
+}
+
+func TestSign_ConnRefusedMapsToUnavailable(t *testing.T) {
+	c := Client{
+		BaseURL:       "http://127.0.0.1:1",
+		HTTPClient:    &http.Client{Timeout: 500 * time.Millisecond},
+		PocketIDToken: auth.StaticToken("a"),
+		WorkloadToken: auth.StaticToken("b"),
+	}
+	_, err := c.Sign(context.Background(), "k", Statement{"_type": "x"})
+	if !errors.Is(err, ErrSignerUnavailable) {
+		t.Fatalf("want ErrSignerUnavailable, got %v", err)
+	}
+}
+
+func TestSign_RequiresWorkloadToken(t *testing.T) {
+	c := Client{BaseURL: "http://localhost", PocketIDToken: auth.StaticToken("a")}
+	_, err := c.Sign(context.Background(), "k", Statement{"_type": "x"})
+	if err == nil {
+		t.Fatal("expected error when WorkloadToken source is missing")
+	}
+}
+
+func TestSign_RequiresPocketIDToken(t *testing.T) {
+	c := Client{BaseURL: "http://localhost", WorkloadToken: auth.StaticToken("a")}
+	_, err := c.Sign(context.Background(), "k", Statement{"_type": "x"})
+	if err == nil {
+		t.Fatal("expected error when PocketIDToken source is missing")
+	}
+}

services/testagent-transform/internal/sink/client.go

@@ -0,0 +1,108 @@
+// Package sink posts a handover_payload to the (phase-1) dummy sink.
+//
+// The payload is sent as the canonical JSON bytes the agent already hashed
+// into the transform attestation's subject digest — a byte-for-byte match
+// is a hard requirement for a downstream verifier, so we send those bytes
+// directly rather than re-marshaling.
+package sink
+
+import (
+	"bytes"
+	"context"
+	"errors"
+	"fmt"
+	"io"
+	"net/http"
+	"net/url"
+	"time"
+
+	"basicstack.de/proofedmesh/services/testagent-transform/internal/auth"
+)
+
+// SchemaHeader carries the payload's schema identifier so the sink knows
+// which decoder to pick. Phase-1 sinks are told to expect "sink.dummy.v1".
+const SchemaHeader = "X-Payload-Schema"
+
+// AttestationHeader carries the transform attestation's content_hash so
+// the sink can resolve the full attestation chain in the TLog without
+// re-parsing the signed envelope.
+const AttestationHeader = "X-Attestation-Ref"
+
+// ErrSinkUnavailable classifies connection errors and 5xx responses.
+var ErrSinkUnavailable = errors.New("sink: dummy-sink unavailable")
+
+// Client is the dummy-sink POST client.
+type Client struct {
+	BaseURL     string
+	HTTPClient  *http.Client
+	TokenSource auth.TokenSource
+}
+
+// DeliverResult is what the agent reports upstream after a sink POST.
+type DeliverResult struct {
+	Status int
+}
+
+// Deliver POSTs payloadBytes to the sink. The caller passes the schema
+// identifier (e.g. "sink.dummy.v1") and the transform attestation's
+// content_hash so both go on the request headers.
+func (c Client) Deliver(ctx context.Context, schema, attestationRef string, payloadBytes []byte) (DeliverResult, error) {
+	if c.BaseURL == "" {
+		return DeliverResult{}, errors.New("sink.Client: BaseURL is empty")
+	}
+	if schema == "" {
+		return DeliverResult{}, errors.New("sink.Client: schema is required")
+	}
+	if attestationRef == "" {
+		return DeliverResult{}, errors.New("sink.Client: attestationRef is required")
+	}
+	if len(payloadBytes) == 0 {
+		return DeliverResult{}, errors.New("sink.Client: payloadBytes is empty")
+	}
+	hc := c.HTTPClient
+	if hc == nil {
+		hc = &http.Client{Timeout: 10 * time.Second}
+	}
+	endpoint, err := url.JoinPath(c.BaseURL, "/api/v1/handover")
+	if err != nil {
+		return DeliverResult{}, fmt.Errorf("sink: build url: %w", err)
+	}
+	req, err := http.NewRequestWithContext(ctx, http.MethodPost, endpoint, bytes.NewReader(payloadBytes))
+	if err != nil {
+		return DeliverResult{}, err
+	}
+	req.Header.Set("Content-Type", "application/json")
+	req.Header.Set("Accept", "application/json")
+	req.Header.Set(SchemaHeader, schema)
+	req.Header.Set(AttestationHeader, attestationRef)
+	if c.TokenSource != nil {
+		tok, err := c.TokenSource.Token(ctx)
+		if err != nil {
+			return DeliverResult{}, fmt.Errorf("sink: token: %w", err)
+		}
+		if tok != "" {
+			req.Header.Set("Authorization", "Bearer "+tok)
+		}
+	}
+	resp, err := hc.Do(req)
+	if err != nil {
+		return DeliverResult{}, fmt.Errorf("%w: %v", ErrSinkUnavailable, err)
+	}
+	defer resp.Body.Close()
+	raw, _ := io.ReadAll(io.LimitReader(resp.Body, 1<<20))
+	switch {
+	case resp.StatusCode >= 200 && resp.StatusCode < 300:
+		return DeliverResult{Status: resp.StatusCode}, nil
+	case resp.StatusCode >= 500:
+		return DeliverResult{}, fmt.Errorf("%w: status %d: %s", ErrSinkUnavailable, resp.StatusCode, truncate(raw, 256))
+	default:
+		return DeliverResult{}, fmt.Errorf("sink: status %d: %s", resp.StatusCode, truncate(raw, 256))
+	}
+}
+
+func truncate(b []byte, n int) string {
+	if len(b) <= n {
+		return string(b)
+	}
+	return string(b[:n]) + "…"
+}

services/testagent-transform/internal/tlog/client.go

@@ -0,0 +1,119 @@
+// Package tlog submits attestation envelopes to the transparency-log per
+// POST /api/v1/log/entries (ADR-0005). The TLog is idempotent on
+// content_hash: re-submitting the same (envelope, content_hash) returns
+// the original log_index.
+package tlog
+
+import (
+	"bytes"
+	"context"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"io"
+	"net/http"
+	"net/url"
+	"time"
+
+	"basicstack.de/proofedmesh/services/testagent-transform/internal/auth"
+	"basicstack.de/proofedmesh/services/testagent-transform/internal/dsse"
+)
+
+// InclusionProof mirrors the server-side ADR-0005 inclusion proof.
+type InclusionProof struct {
+	TreeSize          int64    `json:"tree_size"`
+	TreeRootHash      string   `json:"tree_root_hash"`
+	SignedTreeHeadRef string   `json:"signed_tree_head_ref"`
+	Hashes            []string `json:"hashes"`
+}
+
+// Receipt is what the TLog returns on a successful submit.
+type Receipt struct {
+	LogIndex       int64          `json:"log_index"`
+	ContentHash    string         `json:"content_hash"`
+	LoggedAt       time.Time      `json:"logged_at"`
+	InclusionProof InclusionProof `json:"inclusion_proof"`
+}
+
+// ErrTLogUnavailable classifies connection errors and 5xx responses.
+var ErrTLogUnavailable = errors.New("tlog: transparency-log unavailable")
+
+// Client is the TLog submit client.
+type Client struct {
+	BaseURL     string
+	HTTPClient  *http.Client
+	TokenSource auth.TokenSource
+}
+
+type submitRequest struct {
+	Envelope    dsse.Envelope `json:"envelope"`
+	ContentHash string        `json:"content_hash"`
+}
+
+// Submit posts env + its contentHash to the TLog. Returns the receipt on
+// 200/201 (idempotent repeat / fresh insert) and ErrTLogUnavailable on
+// transport/5xx. Other non-2xx responses are reported with the raw status.
+func (c Client) Submit(ctx context.Context, env dsse.Envelope, contentHash string) (Receipt, error) {
+	if c.BaseURL == "" {
+		return Receipt{}, errors.New("tlog.Client: BaseURL is empty")
+	}
+	hc := c.HTTPClient
+	if hc == nil {
+		hc = &http.Client{Timeout: 10 * time.Second}
+	}
+	body, err := json.Marshal(submitRequest{Envelope: env, ContentHash: contentHash})
+	if err != nil {
+		return Receipt{}, fmt.Errorf("tlog: marshal submit: %w", err)
+	}
+	endpoint, err := url.JoinPath(c.BaseURL, "/api/v1/log/entries")
+	if err != nil {
+		return Receipt{}, fmt.Errorf("tlog: build url: %w", err)
+	}
+	req, err := http.NewRequestWithContext(ctx, http.MethodPost, endpoint, bytes.NewReader(body))
+	if err != nil {
+		return Receipt{}, err
+	}
+	req.Header.Set("Content-Type", "application/json")
+	req.Header.Set("Accept", "application/json")
+	if c.TokenSource != nil {
+		tok, err := c.TokenSource.Token(ctx)
+		if err != nil {
+			return Receipt{}, fmt.Errorf("tlog: token: %w", err)
+		}
+		if tok != "" {
+			req.Header.Set("Authorization", "Bearer "+tok)
+		}
+	}
+	resp, err := hc.Do(req)
+	if err != nil {
+		return Receipt{}, fmt.Errorf("%w: %v", ErrTLogUnavailable, err)
+	}
+	defer resp.Body.Close()
+	raw, _ := io.ReadAll(io.LimitReader(resp.Body, 1<<20))
+	switch {
+	case resp.StatusCode == http.StatusOK, resp.StatusCode == http.StatusCreated:
+		// ok
+	case resp.StatusCode >= 500:
+		return Receipt{}, fmt.Errorf("%w: status %d: %s", ErrTLogUnavailable, resp.StatusCode, truncate(raw, 256))
+	default:
+		return Receipt{}, fmt.Errorf("tlog: status %d: %s", resp.StatusCode, truncate(raw, 256))
+	}
+	var out Receipt
+	if err := json.Unmarshal(raw, &out); err != nil {
+		return Receipt{}, fmt.Errorf("tlog: decode receipt: %w", err)
+	}
+	if out.ContentHash != contentHash {
+		return out, fmt.Errorf("tlog returned content_hash %q != sent %q", out.ContentHash, contentHash)
+	}
+	if out.LogIndex < 0 {
+		return out, fmt.Errorf("tlog returned negative log_index %d", out.LogIndex)
+	}
+	return out, nil
+}
+
+func truncate(b []byte, n int) string {
+	if len(b) <= n {
+		return string(b)
+	}
+	return string(b[:n]) + "…"
+}

services/testagent-transform/internal/tlog/client_test.go

@@ -0,0 +1,72 @@
+package tlog
+
+import (
+	"context"
+	"encoding/json"
+	"errors"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+	"time"
+
+	"basicstack.de/proofedmesh/services/testagent-transform/internal/dsse"
+)
+
+func TestSubmit_HappyPath(t *testing.T) {
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		if r.URL.Path != "/api/v1/log/entries" {
+			http.NotFound(w, r)
+			return
+		}
+		var body struct {
+			Envelope    dsse.Envelope `json:"envelope"`
+			ContentHash string        `json:"content_hash"`
+		}
+		_ = json.NewDecoder(r.Body).Decode(&body)
+		w.Header().Set("Content-Type", "application/json")
+		w.WriteHeader(http.StatusCreated)
+		_ = json.NewEncoder(w).Encode(Receipt{
+			LogIndex:    7,
+			ContentHash: body.ContentHash,
+			LoggedAt:    time.Now(),
+		})
+	}))
+	defer srv.Close()
+	c := Client{BaseURL: srv.URL}
+	r, err := c.Submit(context.Background(), dsse.Envelope{PayloadType: "x", Payload: "aGk"}, "sha256:abc")
+	if err != nil {
+		t.Fatalf("Submit: %v", err)
+	}
+	if r.LogIndex != 7 || r.ContentHash != "sha256:abc" {
+		t.Fatalf("receipt = %+v", r)
+	}
+}
+
+func TestSubmit_5xxMapsToUnavailable(t *testing.T) {
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, _ *http.Request) {
+		http.Error(w, "boom", http.StatusServiceUnavailable)
+	}))
+	defer srv.Close()
+	c := Client{BaseURL: srv.URL}
+	_, err := c.Submit(context.Background(), dsse.Envelope{}, "sha256:abc")
+	if !errors.Is(err, ErrTLogUnavailable) {
+		t.Fatalf("want ErrTLogUnavailable, got %v", err)
+	}
+}
+
+func TestSubmit_ContentHashMismatchIsReported(t *testing.T) {
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, _ *http.Request) {
+		w.Header().Set("Content-Type", "application/json")
+		w.WriteHeader(http.StatusCreated)
+		_ = json.NewEncoder(w).Encode(Receipt{
+			LogIndex:    1,
+			ContentHash: "sha256:different",
+		})
+	}))
+	defer srv.Close()
+	c := Client{BaseURL: srv.URL}
+	_, err := c.Submit(context.Background(), dsse.Envelope{}, "sha256:expected")
+	if err == nil {
+		t.Fatal("expected error on content_hash mismatch")
+	}
+}

services/testagent-transform/internal/transform/runner.go

@@ -0,0 +1,228 @@
+// Package transform wires the five Phase-1 steps of the testagent-transform
+// into a single Execute call:
+//
+//  1. Fetch the approval attestation from the transparency-log by
+//     attestation_ref.
+//  2. Verify the fetched DSSE envelope against a pinned approval-signer
+//     keyring.
+//  3. Build an in-toto v1 Statement with predicateType
+//     "https://basicstack.de/attestations/transform/v1", operation
+//     "expense.map_to_sink", and subject.digest.sha256 =
+//     canonical_sha256(handover_payload).
+//  4. Call the signing-service with BOTH identities (Pocket-ID bearer +
+//     projected SA token) to obtain a DSSE envelope + content_hash.
+//  5. Submit the envelope to the transparency-log.
+//  6. POST the exact canonical handover_payload bytes to the dummy-sink.
+//
+// Failures are classified so a Phase-1 ops dashboard can distinguish an
+// invalid upstream approval (reject at step 2, before any new signature
+// is created) from a signing-service denial (step 4).
+package transform
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"time"
+
+	"basicstack.de/proofedmesh/services/testagent-transform/internal/approval"
+	"basicstack.de/proofedmesh/services/testagent-transform/internal/canonical"
+	"basicstack.de/proofedmesh/services/testagent-transform/internal/dsse"
+	"basicstack.de/proofedmesh/services/testagent-transform/internal/signer"
+	"basicstack.de/proofedmesh/services/testagent-transform/internal/sink"
+	"basicstack.de/proofedmesh/services/testagent-transform/internal/tlog"
+)
+
+// SchemaRef names and versions a schema. Mirrors the architecture doc's
+// `schema.input`/`schema.output` shape.
+type SchemaRef struct {
+	Name    string `json:"name"`
+	Version string `json:"version"`
+}
+
+// Config holds the per-agent fixed parameters. All fields are required.
+type Config struct {
+	// Actor is the agent's registry id (e.g. "agent-testagent-transform").
+	Actor string
+	// Operation is the OPA-vetted transformation name
+	// ("expense.map_to_sink" in Phase 1).
+	Operation string
+	// SinkTarget is the logical sink identifier the architecture doc uses
+	// to tie the transform to a sink policy ("sink:dummy-sink" here).
+	SinkTarget string
+	// SigningKeyRef is the OpenBao Transit key reference the
+	// signing-service uses on behalf of this agent
+	// ("trust-api/agent-testagent-transform-2026-q4" in Phase 1).
+	SigningKeyRef string
+	// Input / Output schemas carried through on the attestation so the
+	// verifier knows which decoder to run.
+	Input, Output SchemaRef
+	// TransformVersion is the agent's own version string, carried into
+	// the attestation so bugfixes are auditable.
+	TransformVersion string
+	// SinkPayloadSchema is the schema identifier the sink expects on the
+	// `X-Payload-Schema` header. Phase-1: "sink.dummy.v1".
+	SinkPayloadSchema string
+}
+
+// ApprovalFetcher pulls an approval entry from the TLog by attestation_ref.
+type ApprovalFetcher interface {
+	Fetch(ctx context.Context, attestationRef string) (approval.Entry, error)
+}
+
+// SignerClient produces a signed DSSE envelope. Prod wiring is a
+// signer.Client; tests swap in a fake.
+type SignerClient interface {
+	Sign(ctx context.Context, keyRef string, stmt signer.Statement) (signer.SignedResult, error)
+}
+
+// TLogSubmitter adds the envelope to the transparency log.
+type TLogSubmitter interface {
+	Submit(ctx context.Context, env dsse.Envelope, contentHash string) (tlog.Receipt, error)
+}
+
+// SinkDeliverer posts the handover_payload bytes to the sink.
+type SinkDeliverer interface {
+	Deliver(ctx context.Context, schema, attestationRef string, payloadBytes []byte) (sink.DeliverResult, error)
+}
+
+// Request is a single transform invocation. HandoverPayload is JSON-shaped
+// (`map[string]any` after unmarshal); the agent canonicalises it to compute
+// the subject digest and ships the same canonical bytes to the sink.
+type Request struct {
+	WorkflowID      string
+	ApprovalRef     string
+	HandoverPayload map[string]any
+}
+
+// Result is what the agent reports after a successful Execute.
+type Result struct {
+	TransformRef    string
+	LogIndex        int64
+	SinkStatus      int
+	HandoverHashHex string
+}
+
+// Runner is the orchestration root.
+type Runner struct {
+	Config
+
+	Approvals        ApprovalFetcher
+	ApprovalKeyring  dsse.Keyring
+	Signer           SignerClient
+	TLog             TLogSubmitter
+	Sink             SinkDeliverer
+	Now              func() time.Time
+}
+
+// ErrInvalidApproval wraps a DSSE verification failure on the fetched
+// approval envelope. The runner stops immediately — no new attestation
+// should be issued on top of an untrusted approval.
+var ErrInvalidApproval = errors.New("transform: fetched approval attestation did not verify")
+
+// Execute runs the five-step pipeline.
+func (r *Runner) Execute(ctx context.Context, req Request) (Result, error) {
+	if err := r.validate(req); err != nil {
+		return Result{}, err
+	}
+
+	ap, err := r.Approvals.Fetch(ctx, req.ApprovalRef)
+	if err != nil {
+		return Result{}, fmt.Errorf("fetch approval %s: %w", req.ApprovalRef, err)
+	}
+
+	if _, err := dsse.Verify(ap.Envelope, r.ApprovalKeyring); err != nil {
+		return Result{}, fmt.Errorf("%w: %v", ErrInvalidApproval, err)
+	}
+
+	payloadBytes, err := canonical.Marshal(req.HandoverPayload)
+	if err != nil {
+		return Result{}, fmt.Errorf("canonical handover_payload: %w", err)
+	}
+	payloadHashHex := canonical.SHA256Hex(payloadBytes)
+
+	stmt := r.buildStatement(req, payloadHashHex)
+
+	signed, err := r.Signer.Sign(ctx, r.SigningKeyRef, stmt)
+	if err != nil {
+		return Result{}, fmt.Errorf("sign transform statement: %w", err)
+	}
+
+	receipt, err := r.TLog.Submit(ctx, signed.Envelope, signed.ContentHash)
+	if err != nil {
+		return Result{}, fmt.Errorf("tlog submit transform: %w", err)
+	}
+
+	deliv, err := r.Sink.Deliver(ctx, r.SinkPayloadSchema, signed.ContentHash, payloadBytes)
+	if err != nil {
+		return Result{}, fmt.Errorf("sink deliver: %w", err)
+	}
+
+	return Result{
+		TransformRef:    signed.ContentHash,
+		LogIndex:        receipt.LogIndex,
+		SinkStatus:      deliv.Status,
+		HandoverHashHex: payloadHashHex,
+	}, nil
+}
+
+func (r *Runner) validate(req Request) error {
+	if r.Approvals == nil || r.ApprovalKeyring == nil || r.Signer == nil || r.TLog == nil || r.Sink == nil {
+		return errors.New("transform.Runner: missing dependency wiring")
+	}
+	if r.Actor == "" || r.Operation == "" || r.SinkTarget == "" || r.SigningKeyRef == "" {
+		return errors.New("transform.Runner: Config missing required field (Actor/Operation/SinkTarget/SigningKeyRef)")
+	}
+	if r.SinkPayloadSchema == "" {
+		return errors.New("transform.Runner: Config.SinkPayloadSchema is required")
+	}
+	if r.Input.Name == "" || r.Input.Version == "" || r.Output.Name == "" || r.Output.Version == "" {
+		return errors.New("transform.Runner: Config.Input/Output schema is required")
+	}
+	if req.WorkflowID == "" || req.ApprovalRef == "" || len(req.HandoverPayload) == 0 {
+		return errors.New("transform.Runner: Request missing required field (WorkflowID/ApprovalRef/HandoverPayload)")
+	}
+	return nil
+}
+
+func (r *Runner) buildStatement(req Request, payloadHashHex string) signer.Statement {
+	issuedAt := r.now().UTC().Format(time.RFC3339)
+	return signer.Statement{
+		"_type": "https://in-toto.io/Statement/v1",
+		"subject": []any{
+			map[string]any{
+				"name": "transform/" + req.WorkflowID + "/handover",
+				"digest": map[string]any{
+					"sha256": payloadHashHex,
+				},
+			},
+		},
+		"predicateType": "https://basicstack.de/attestations/transform/v1",
+		"predicate": map[string]any{
+			"workflow_id":  req.WorkflowID,
+			"actor":        r.Actor,
+			"operation":    r.Operation,
+			"sink_target":  r.SinkTarget,
+			"approval_ref": req.ApprovalRef,
+			"materials": []any{
+				map[string]any{
+					"name":            "approval/" + req.ApprovalRef,
+					"attestation_ref": req.ApprovalRef,
+				},
+			},
+			"schema": map[string]any{
+				"input":  map[string]any{"name": r.Input.Name, "version": r.Input.Version},
+				"output": map[string]any{"name": r.Output.Name, "version": r.Output.Version},
+			},
+			"transform_version": r.TransformVersion,
+			"issued_at":         issuedAt,
+		},
+	}
+}
+
+func (r *Runner) now() time.Time {
+	if r.Now != nil {
+		return r.Now()
+	}
+	return time.Now()
+}

services/testagent-transform/internal/transform/runner_test.go

@@ -0,0 +1,405 @@
+package transform
+
+import (
+	"bytes"
+	"context"
+	"crypto/ed25519"
+	"crypto/rand"
+	"encoding/base64"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"io"
+	"net/http"
+	"net/http/httptest"
+	"strings"
+	"testing"
+	"time"
+
+	"basicstack.de/proofedmesh/services/testagent-transform/internal/approval"
+	"basicstack.de/proofedmesh/services/testagent-transform/internal/auth"
+	"basicstack.de/proofedmesh/services/testagent-transform/internal/canonical"
+	"basicstack.de/proofedmesh/services/testagent-transform/internal/dsse"
+	"basicstack.de/proofedmesh/services/testagent-transform/internal/signer"
+	"basicstack.de/proofedmesh/services/testagent-transform/internal/sink"
+	"basicstack.de/proofedmesh/services/testagent-transform/internal/tlog"
+)
+
+// mocks wires httptest servers for approval-service (via TLog GET),
+// signing-service, transparency-log (POST), and the dummy-sink.
+type mocks struct {
+	approvalSrv *httptest.Server
+	signSrv     *httptest.Server
+	tlogSrv     *httptest.Server
+	sinkSrv     *httptest.Server
+
+	approvalPub   ed25519.PublicKey
+	transformPub  ed25519.PublicKey
+	transformPriv ed25519.PrivateKey
+
+	sinkPayload   []byte
+	sinkSchema    string
+	sinkAttestRef string
+	sinkCalled    bool
+
+	tlogSubmitted []string // sha256:… content_hashes seen on POST /log/entries
+}
+
+// buildMocks creates all four backends. By default the approval envelope
+// is validly signed by approvalPriv (keyring key id "approval-key").
+// Caller may override behaviour via opts before calling run.
+type mockOpts struct {
+	// tamperApproval replaces the valid approval signature with a bogus
+	// one so DSSE verify fails before any sign-call happens.
+	tamperApproval bool
+	// signDenies makes the signing-service answer 403 signing_denied so
+	// the agent surfaces ErrSigningDenied.
+	signDenies bool
+	// pocketIDTokenEmpty makes the Pocket-ID TokenSource return "" so the
+	// signer.Client refuses to even send the request.
+	pocketIDTokenEmpty bool
+}
+
+const (
+	approvalKeyID  = "approval-key"
+	transformKeyID = "trust-api/agent-testagent-transform-2026-q4"
+	pocketIDBearer = "pocket-id-access-token-for-testagent-transform"
+	workloadToken  = "projected-sa-token-trust-api"
+	attestationRef = "sha256:1111111111111111111111111111111111111111111111111111111111111111"
+)
+
+func buildMocks(t *testing.T, opts mockOpts) *mocks {
+	t.Helper()
+	m := &mocks{sinkSchema: "sink.dummy.v1"}
+
+	// Keys.
+	approvalPub, approvalPriv, err := ed25519.GenerateKey(rand.Reader)
+	if err != nil {
+		t.Fatal(err)
+	}
+	transformPub, transformPriv, err := ed25519.GenerateKey(rand.Reader)
+	if err != nil {
+		t.Fatal(err)
+	}
+	m.approvalPub = approvalPub
+	m.transformPub = transformPub
+	m.transformPriv = transformPriv
+
+	// A real DSSE envelope the agent must fetch, verify, and reference.
+	approvalPayload := map[string]any{
+		"_type":         "https://in-toto.io/Statement/v1",
+		"predicateType": "https://basicstack.de/attestations/approval/v1",
+		"subject": []any{
+			map[string]any{
+				"name":   "approval/APR-TEST",
+				"digest": map[string]any{"sha256": "deadbeef"},
+			},
+		},
+		"predicate": map[string]any{"approval_id": "APR-TEST"},
+	}
+	approvalEnv := dsseSign(t, "application/vnd.in-toto+json", approvalPayload, approvalKeyID, approvalPriv)
+	if opts.tamperApproval {
+		// Replace sig with bogus bytes so Verify fails.
+		approvalEnv.Signatures[0].Sig = base64.RawURLEncoding.EncodeToString(bytes.Repeat([]byte{0xAA}, ed25519.SignatureSize))
+	}
+
+	// approvalSrv: TLog read endpoint GET /api/v1/log/entries/{content_hash}.
+	m.approvalSrv = httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		if r.Method != http.MethodGet {
+			http.Error(w, "method", http.StatusMethodNotAllowed)
+			return
+		}
+		if r.URL.Path != "/api/v1/log/entries/"+attestationRef {
+			http.NotFound(w, r)
+			return
+		}
+		entry := approval.Entry{
+			ContentHash: attestationRef,
+			Envelope:    approvalEnv,
+			LogIndex:    42,
+			LoggedAt:    time.Date(2026, 10, 25, 20, 0, 0, 0, time.UTC),
+		}
+		w.Header().Set("Content-Type", "application/json")
+		_ = json.NewEncoder(w).Encode(entry)
+	}))
+
+	// signSrv: POST /api/v1/sign/dsse — requires BOTH identities and
+	// returns a real DSSE envelope signed by transformPriv so the TLog
+	// path can verify content_hash consistency.
+	m.signSrv = httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		if r.URL.Path != "/api/v1/sign/dsse" || r.Method != http.MethodPost {
+			http.NotFound(w, r)
+			return
+		}
+		if got := r.Header.Get("Authorization"); got != "Bearer "+pocketIDBearer {
+			http.Error(w, `{"error":{"code":"unauthorized","message":"bad bearer"}}`, http.StatusUnauthorized)
+			return
+		}
+		if got := r.Header.Get(signer.WorkloadTokenHeader); got != workloadToken {
+			http.Error(w, `{"error":{"code":"unauthorized","message":"bad workload token"}}`, http.StatusUnauthorized)
+			return
+		}
+		if opts.signDenies {
+			http.Error(w, `{"error":{"code":"signing_denied","message":"policy denies key_ref"}}`, http.StatusForbidden)
+			return
+		}
+		var body struct {
+			KeyRef    string         `json:"key_ref"`
+			Statement map[string]any `json:"statement"`
+		}
+		if err := json.NewDecoder(r.Body).Decode(&body); err != nil {
+			http.Error(w, "decode", http.StatusBadRequest)
+			return
+		}
+		if body.KeyRef != transformKeyID {
+			http.Error(w, `{"error":{"code":"bad_request","message":"unexpected key_ref"}}`, http.StatusBadRequest)
+			return
+		}
+
+		env := dsseSign(t, "application/vnd.in-toto+json", body.Statement, transformKeyID, transformPriv)
+		envRaw, _ := canonical.Marshal(env)
+		contentHash := "sha256:" + canonical.SHA256Hex(envRaw)
+		resp := signer.SignedResult{
+			Envelope:    env,
+			ContentHash: contentHash,
+			SignedAt:    time.Date(2026, 10, 25, 20, 0, 0, 0, time.UTC),
+		}
+		w.Header().Set("Content-Type", "application/json")
+		_ = json.NewEncoder(w).Encode(resp)
+	}))
+
+	// tlogSrv: POST /api/v1/log/entries. Verifies content_hash matches
+	// the request's envelope then returns a canned receipt.
+	m.tlogSrv = httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		if r.URL.Path != "/api/v1/log/entries" || r.Method != http.MethodPost {
+			http.NotFound(w, r)
+			return
+		}
+		var body struct {
+			Envelope    dsse.Envelope `json:"envelope"`
+			ContentHash string        `json:"content_hash"`
+		}
+		if err := json.NewDecoder(r.Body).Decode(&body); err != nil {
+			http.Error(w, "decode", http.StatusBadRequest)
+			return
+		}
+		// Independent recompute: the TLog mock re-canonicalises and
+		// confirms the submitted content_hash really does name this
+		// envelope.
+		envRaw, _ := canonical.Marshal(body.Envelope)
+		got := "sha256:" + canonical.SHA256Hex(envRaw)
+		if got != body.ContentHash {
+			http.Error(w, fmt.Sprintf(`{"error":"content_hash mismatch: got %s want %s"}`, got, body.ContentHash), http.StatusConflict)
+			return
+		}
+		m.tlogSubmitted = append(m.tlogSubmitted, body.ContentHash)
+		rcpt := tlog.Receipt{
+			LogIndex:    1234,
+			ContentHash: body.ContentHash,
+			LoggedAt:    time.Date(2026, 10, 25, 20, 0, 1, 0, time.UTC),
+			InclusionProof: tlog.InclusionProof{
+				TreeSize:          1235,
+				TreeRootHash:      "sha256:" + strings.Repeat("a", 64),
+				SignedTreeHeadRef: "sha256:" + strings.Repeat("b", 64),
+				Hashes:            []string{"sha256:" + strings.Repeat("c", 64)},
+			},
+		}
+		w.Header().Set("Content-Type", "application/json")
+		w.WriteHeader(http.StatusCreated)
+		_ = json.NewEncoder(w).Encode(rcpt)
+	}))
+
+	// sinkSrv: POST /api/v1/handover; captures body + headers so the
+	// test can assert the agent sent exactly the canonical bytes.
+	m.sinkSrv = httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		if r.URL.Path != "/api/v1/handover" || r.Method != http.MethodPost {
+			http.NotFound(w, r)
+			return
+		}
+		m.sinkCalled = true
+		m.sinkSchema = r.Header.Get(sink.SchemaHeader)
+		m.sinkAttestRef = r.Header.Get(sink.AttestationHeader)
+		m.sinkPayload, _ = io.ReadAll(r.Body)
+		w.WriteHeader(http.StatusAccepted)
+	}))
+
+	t.Cleanup(func() {
+		m.approvalSrv.Close()
+		m.signSrv.Close()
+		m.tlogSrv.Close()
+		m.sinkSrv.Close()
+	})
+	return m
+}
+
+func newRunner(t *testing.T, m *mocks, opts mockOpts) *Runner {
+	t.Helper()
+	pocketIDToken := auth.StaticToken(pocketIDBearer)
+	if opts.pocketIDTokenEmpty {
+		pocketIDToken = ""
+	}
+	return &Runner{
+		Config: Config{
+			Actor:             "agent-testagent-transform",
+			Operation:         "expense.map_to_sink",
+			SinkTarget:        "sink:dummy-sink",
+			SigningKeyRef:     transformKeyID,
+			Input:             SchemaRef{Name: "expense.canonical", Version: "1.2.0"},
+			Output:            SchemaRef{Name: "sink.db.expense", Version: "1.2.0"},
+			TransformVersion:  "0.1.0",
+			SinkPayloadSchema: "sink.dummy.v1",
+		},
+		Approvals: approval.Client{
+			BaseURL: m.approvalSrv.URL,
+		},
+		ApprovalKeyring: dsse.Keyring{approvalKeyID: m.approvalPub},
+		Signer: signer.Client{
+			BaseURL:       m.signSrv.URL,
+			PocketIDToken: pocketIDToken,
+			WorkloadToken: auth.StaticToken(workloadToken),
+		},
+		TLog: tlog.Client{BaseURL: m.tlogSrv.URL},
+		Sink: sink.Client{BaseURL: m.sinkSrv.URL},
+		Now:  func() time.Time { return time.Date(2026, 10, 25, 20, 0, 0, 0, time.UTC) },
+	}
+}
+
+func sampleRequest() Request {
+	return Request{
+		WorkflowID:  "WF-TEST-1",
+		ApprovalRef: attestationRef,
+		HandoverPayload: map[string]any{
+			"schema": map[string]any{"name": "sink.dummy.v1", "version": "1.0.0"},
+			"items": []any{
+				map[string]any{"line": "1", "amount": "12.34"},
+			},
+			"workflow_id": "WF-TEST-1",
+		},
+	}
+}
+
+// --- happy path ---
+
+func TestExecute_HappyPath(t *testing.T) {
+	m := buildMocks(t, mockOpts{})
+	r := newRunner(t, m, mockOpts{})
+	req := sampleRequest()
+
+	res, err := r.Execute(context.Background(), req)
+	if err != nil {
+		t.Fatalf("Execute: %v", err)
+	}
+
+	// Content-hash of the handover_payload we sent to the sink must
+	// equal the subject digest the agent signed into the transform
+	// attestation.
+	wantBytes, _ := canonical.Marshal(req.HandoverPayload)
+	wantHash := canonical.SHA256Hex(wantBytes)
+	if res.HandoverHashHex != wantHash {
+		t.Fatalf("HandoverHashHex = %q, want %q", res.HandoverHashHex, wantHash)
+	}
+	if !m.sinkCalled {
+		t.Fatal("sink was never called")
+	}
+	if !bytes.Equal(m.sinkPayload, wantBytes) {
+		t.Fatalf("sink payload bytes differ:\n got %q\nwant %q", m.sinkPayload, wantBytes)
+	}
+	if m.sinkSchema != "sink.dummy.v1" {
+		t.Fatalf("sink schema header = %q", m.sinkSchema)
+	}
+	if m.sinkAttestRef != res.TransformRef {
+		t.Fatalf("sink attestation header = %q, want %q", m.sinkAttestRef, res.TransformRef)
+	}
+
+	// TLog must have seen exactly our transform content_hash.
+	if len(m.tlogSubmitted) != 1 || m.tlogSubmitted[0] != res.TransformRef {
+		t.Fatalf("tlog submits = %v, want [%q]", m.tlogSubmitted, res.TransformRef)
+	}
+	if res.LogIndex == 0 {
+		t.Fatalf("LogIndex not set")
+	}
+	if res.SinkStatus != http.StatusAccepted {
+		t.Fatalf("SinkStatus = %d, want 202", res.SinkStatus)
+	}
+}
+
+// --- negative: approval signature invalid ---
+
+func TestExecute_InvalidApprovalSignature_StopsBeforeSign(t *testing.T) {
+	m := buildMocks(t, mockOpts{tamperApproval: true})
+	r := newRunner(t, m, mockOpts{})
+
+	_, err := r.Execute(context.Background(), sampleRequest())
+	if err == nil {
+		t.Fatal("expected error on invalid approval signature")
+	}
+	if !errors.Is(err, ErrInvalidApproval) {
+		t.Fatalf("expected ErrInvalidApproval, got %v", err)
+	}
+	if len(m.tlogSubmitted) != 0 {
+		t.Fatalf("tlog must not be touched when approval is invalid; saw %v", m.tlogSubmitted)
+	}
+	if m.sinkCalled {
+		t.Fatal("sink must not be touched when approval is invalid")
+	}
+}
+
+// --- negative: signing-service refuses (403 signing_denied) ---
+
+func TestExecute_SigningDenied_SurfacesError(t *testing.T) {
+	m := buildMocks(t, mockOpts{signDenies: true})
+	r := newRunner(t, m, mockOpts{})
+
+	_, err := r.Execute(context.Background(), sampleRequest())
+	if err == nil {
+		t.Fatal("expected error when signing-service denies")
+	}
+	if !errors.Is(err, signer.ErrSigningDenied) {
+		t.Fatalf("expected signer.ErrSigningDenied, got %v", err)
+	}
+	if len(m.tlogSubmitted) != 0 {
+		t.Fatalf("tlog must not be touched on sign denial")
+	}
+	if m.sinkCalled {
+		t.Fatal("sink must not be touched on sign denial")
+	}
+}
+
+// --- negative: both identities required ---
+
+func TestExecute_MissingPocketIDToken_FailsBeforeNetwork(t *testing.T) {
+	m := buildMocks(t, mockOpts{})
+	r := newRunner(t, m, mockOpts{pocketIDTokenEmpty: true})
+
+	_, err := r.Execute(context.Background(), sampleRequest())
+	if err == nil {
+		t.Fatal("expected error when Pocket-ID token is empty")
+	}
+	if !strings.Contains(err.Error(), "pocket-id token is empty") {
+		t.Fatalf("expected pocket-id token error, got %v", err)
+	}
+}
+
+// --- helpers ---
+
+// dsseSign produces a DSSE envelope with payloadBytes = canonical(stmt)
+// and signatures = [ed25519(PAE(payloadType, payloadBytes))].
+func dsseSign(t *testing.T, payloadType string, stmt map[string]any, keyID string, priv ed25519.PrivateKey) dsse.Envelope {
+	t.Helper()
+	payloadBytes, err := canonical.Marshal(stmt)
+	if err != nil {
+		t.Fatalf("canonical: %v", err)
+	}
+	payloadB64 := base64.RawURLEncoding.EncodeToString(payloadBytes)
+	pae := []byte(fmt.Sprintf("DSSEv1 %d %s %d ", len(payloadType), payloadType, len(payloadBytes)))
+	pae = append(pae, payloadBytes...)
+	sig := ed25519.Sign(priv, pae)
+	return dsse.Envelope{
+		PayloadType: payloadType,
+		Payload:     payloadB64,
+		Signatures: []dsse.EnvelopeSignature{{
+			KeyID: keyID,
+			Sig:   base64.RawURLEncoding.EncodeToString(sig),
+		}},
+	}
+}