feat(iios): context-attestation verifier — the July 12 stolen-token proof (§1)

A valid actor token is no longer enough. This adds the trust-layer core so IIOS
can require a signed CONTEXT ATTESTATION from an authorized parent (AppShell etc.)
before a privileged request — defeating a hacked app replaying a stolen token.

- prisma: IiosClientRegistry (registered clients allowed to attest, per app) +
  IiosAttestationNonce (single-use replay ledger). Migration applied.
- ContextAttestationVerifier + ports (ClientRegistryPort, NonceStorePort) + a dev
  signer. Verifies: registered+active client, signature, aud=iios, app_id matches
  the token AND is allowed for the client, freshness, single-use nonce. Fail-closed.
- Prisma-backed stores; nonce reserve is atomic via the unique PK (P2002 = replay).
- Tests (9 pass): happy path + the five rejection cases the CEO named
  (unknown client, wrong audience, expired, replayed nonce, app-mismatch) +
  forged-signature + disabled-client; a DB atomicity test (skips if engine offline).

Decoupled from the request path on purpose — wiring it into the messaging guard
(the three-proof gate) + demoting be-crm to an attestation forwarder is the next step.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

packages/iios-service/prisma/migrations/20260713200417_add_context_attestation/migration.sql

@@ -0,0 +1,24 @@
+-- Trust plane (July 12): context attestation client registry + nonce replay ledger.
+CREATE TABLE "IiosClientRegistry" (
+    "clientId" TEXT NOT NULL,
+    "clientType" TEXT NOT NULL,
+    "ownerService" TEXT,
+    "allowedAppIds" TEXT[] NOT NULL DEFAULT ARRAY[]::TEXT[],
+    "attestSecret" TEXT,
+    "jwksUri" TEXT,
+    "spiffeId" TEXT,
+    "status" TEXT NOT NULL DEFAULT 'ACTIVE',
+    "createdAt" TIMESTAMP(3) NOT NULL DEFAULT CURRENT_TIMESTAMP,
+    "updatedAt" TIMESTAMP(3) NOT NULL,
+    CONSTRAINT "IiosClientRegistry_pkey" PRIMARY KEY ("clientId")
+);
+
+CREATE TABLE "IiosAttestationNonce" (
+    "nonce" TEXT NOT NULL,
+    "clientId" TEXT NOT NULL,
+    "expiresAt" TIMESTAMP(3) NOT NULL,
+    "firstSeenAt" TIMESTAMP(3) NOT NULL DEFAULT CURRENT_TIMESTAMP,
+    CONSTRAINT "IiosAttestationNonce_pkey" PRIMARY KEY ("nonce")
+);
+
+CREATE INDEX "IiosAttestationNonce_expiresAt_idx" ON "IiosAttestationNonce"("expiresAt");

packages/iios-service/prisma/schema.prisma

@@ -1321,3 +1321,31 @@ model IiosDlqItem {
   @@unique([consumerName, sourceId])
   @@index([scopeId, status])
 }
+
+// ─── Trust plane (July 12) — context attestation ──────────────────
+// Registered clients/BFFs/adapters allowed to call IIOS and attest context on
+// behalf of an app. A valid actor token is NOT enough; the caller must present a
+// context attestation signed by one of these registered clients.
+model IiosClientRegistry {
+  clientId      String   @id
+  clientType    String   // APPSHELL | SUPPORT_BFF | ADAPTER | CALENDAR | SERVICE
+  ownerService  String?
+  allowedAppIds String[] // which app_ids this client may attest for
+  attestSecret  String?  // dev: shared HS256 signing key (AppShell's key stand-in)
+  jwksUri       String?  // prod: verify the attestation signature via JWKS
+  spiffeId      String?  // prod: workload identity for mTLS proof
+  status        String   @default("ACTIVE") // ACTIVE | DISABLED
+  createdAt     DateTime @default(now())
+  updatedAt     DateTime @updatedAt
+}
+
+// Single-use nonce ledger: once a context attestation's nonce is seen it can
+// never be replayed. Reserve-if-absent (unique PK) makes the check atomic.
+model IiosAttestationNonce {
+  nonce       String   @id
+  clientId    String
+  expiresAt   DateTime
+  firstSeenAt DateTime @default(now())
+
+  @@index([expiresAt])
+}