diff --git a/docs/cfav-retired-saml-signing-key-evidence.md b/docs/cfav-retired-saml-signing-key-evidence.md
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+# CFAV: Retired SAML Signing Key Trust-Edge Evidence (Issue #90)
+
+## Scope
+
+This is a **non-production synthetic acceptance fixture** for existing TrustDecay / SCIM-RE / RAP / Execution Exchange. It is **not a SAML XML signature implementation, live SAML relying-party test, post-quantum cryptanalysis, or production certification**.
+
+It uses actual RSA-2048/SHA-256 test-only signatures over a JSON assertion analog, two simulated relying parties with different pinned keys, the existing TTP `resolveTrustRoute()` on a revoked trust path, and independently pinned Ed25519 observer signatures over test observations. Keys are ephemeral and never committed.
+
+Run: `node --test packages/trust-routing-engine/tests/retired-key-assurance.test.mjs` or `npm run test:trust-routing`.
+
+## Evidence semantics
+
+- `NATIVE_REJECTED`: a host-pinned test observer signed an observation that the synthetic target rejected K1. This does not prove a real vendor SAML SP rejected XML.
+- `NATIVE_ACCEPTANCE_UNCONTROLLED`: an inventoried SP accepted a K1-signed test assertion; no blocked effect was observed. Do not claim it is governed.
+- `RESIDUAL_TRUST_BLOCKED_AT_EFFECT`: simulated native SP accepted K1, and the **same assertion challenge** was blocked at the protected effect by a test call through existing TrustRoute. Residual native trust remains and must be disclosed.
+- `UNPROTECTED_EFFECT`: signed observation that the protected consequence executed; negative counterexample to safety.
+- `UNKNOWN`: no appropriately scoped signed and fresh observation. Never silently treat unknown as safe.
+
+Receipts prove what a verifier reported, not independently that a real SP behaved as reported. A caller cannot earn verification by setting a `verified: true` boolean. The assessment requires a host-pinned observer key. The trusted host must independently control both observation collection and key trust. Synthetic signing material and `pinnedObserverKeys` shown in test code are **not** production key custody.
+
+## Next controlled integration gate
+
+1. Inventory actual `(issuer ID, signing-key SHA-256 SPKI fingerprint, relying-party ID, owner, configuration source)` trust edges, including manual pins and unobserved applications; do not treat inventory completeness as assumed.
+2. Deploy two isolated, approved SAML XML service-provider test environments with synthetic users, test-only certificates and a properly configured assertion validator.
+3. Produce independent native SP evidence for active K2 acceptance, K1 rejection in dynamic SP, K1 acceptance at deliberately pinned SP, and positive/negative audience, destination, InResponseTo, Conditions, subject confirmation, replay and issuer tests.
+4. Protect a specific downstream action with the actual non-demo BlockSiFr authority path. Test native bypass routes and side effects with target-side audit instrumentation. Record genuine DENY and physical effect outcome separately.
+5. Ensure signed observer evidence is rooted in an enrolled, rotated and revocable production trust registry. Test stale, missing, tampered, wrong-tenant, replayed, and revoked observer evidence.
+6. Produce a report of `N` known edges, `R` native rejections, `B` residual native accepts with protected downstream blocks, `E` observed executions, and `U` unknowns. Never claim full coverage when `U > 0` or discovery is incomplete.
+
+**Acceptance claim allowed today:** Source-verified test harness demonstrating the difference between key retirement, native relying-party trust, and protected downstream execution. **Not allowed:** “Every relying party rejects a retired SAML key.”
diff --git a/packages/trust-routing-engine/src/retired-key-assurance.js b/packages/trust-routing-engine/src/retired-key-assurance.js
new file mode 100644
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+++ b/packages/trust-routing-engine/src/retired-key-assurance.js
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+import { createPublicKey, verify } from 'node:crypto'
+
+// Read-only evidence assessment. This does not verify SAML XML, authenticate a user,
+// mutate relying-party configuration, or authorize an execution.
+const signedFields = [
+  'runId', 'observerId', 'issuerId', 'relyingPartyId', 'keyFingerprint',
+  'challengeId', 'kind', 'outcome', 'observedAt'
+]
+const outcomes = {
+  native_assertion: new Set(['ACCEPTED', 'REJECTED']),
+  protected_effect: new Set(['EXECUTED', 'BLOCKED'])
+}
+const fingerprintPattern = /^[a-f0-9]{64}$/
+
+export function canonicalObservation(observation) {
+  if (!observation || signedFields.some(k => typeof observation[k] !== 'string' || !observation[k])) {
+    throw new Error('incomplete_observation')
+  }
+  if (!fingerprintPattern.test(observation.keyFingerprint)) throw new Error('invalid_key_fingerprint')
+  if (!outcomes[observation.kind]?.has(observation.outcome)) throw new Error('invalid_outcome')
+  return Buffer.from(JSON.stringify(Object.fromEntries(signedFields.map(k => [k, observation[k]]))), 'utf8')
+}
+
+function verifyObservation(observation, { issuerId, keyFingerprint, runId, pinnedObserverKeys, nowMs, maxAgeMs }) {
+  try {
+    if (observation.issuerId !== issuerId || observation.keyFingerprint !== keyFingerprint || observation.runId !== runId) return false
+    const observedAt = Date.parse(observation.observedAt)
+    if (!Number.isFinite(observedAt) || observedAt > nowMs || nowMs - observedAt > maxAgeMs) return false
+    const publicKey = pinnedObserverKeys[observation.observerId]
+    if (!publicKey || typeof observation.signature !== 'string' || !/^[A-Za-z0-9+/]+={0,2}$/.test(observation.signature)) return false
+    return verify(null, canonicalObservation(observation), createPublicKey(publicKey), Buffer.from(observation.signature, 'base64'))
+  } catch {
+    return false
+  }
+}
+
+/**
+ * Classifies observed trust edges without claiming that an observation is genuine
+ * merely because a caller says so. Observer keys must be pinned by the trusted host.
+ * An accepted native assertion is NEVER reported as native retirement success.
+ */
+export function assessRetiredKeyCoverage({
+  issuerId, keyFingerprint, runId, relyingPartyIds, observations = [],
+  pinnedObserverKeys, assessedAt, maxObservationAgeSeconds = 3600
+}) {
+  if (!issuerId || !runId || !fingerprintPattern.test(keyFingerprint ?? '')) throw new Error('invalid_assessment_scope')
+  if (!Array.isArray(relyingPartyIds) || relyingPartyIds.length === 0 ||
+      relyingPartyIds.some(id => typeof id !== 'string' || !id) ||
+      new Set(relyingPartyIds).size !== relyingPartyIds.length) throw new Error('invalid_relying_party_inventory')
+  if (!Array.isArray(observations) || !pinnedObserverKeys || typeof pinnedObserverKeys !== 'object') throw new Error('invalid_evidence_input')
+  const nowMs = Date.parse(assessedAt)
+  if (!Number.isFinite(nowMs) || !Number.isFinite(maxObservationAgeSeconds) || maxObservationAgeSeconds <= 0) throw new Error('invalid_evaluation_time')
+  const verified = observations.filter(o => relyingPartyIds.includes(o?.relyingPartyId) && verifyObservation(o, {
+    issuerId, keyFingerprint, runId, pinnedObserverKeys, nowMs,
+    maxAgeMs: maxObservationAgeSeconds * 1000
+  }))
+  const edges = relyingPartyIds.map(relyingPartyId => {
+    const party = verified.filter(o => o.relyingPartyId === relyingPartyId)
+    const native = party.filter(o => o.kind === 'native_assertion')
+    const effects = party.filter(o => o.kind === 'protected_effect')
+    // Any observed acceptance defeats the claim that this SP rejects K1.
+    const nativeOutcome = native.some(o => o.outcome === 'ACCEPTED') ? 'ACCEPTED' :
+      native.some(o => o.outcome === 'REJECTED') ? 'REJECTED' : 'UNKNOWN'
+    // A block only constrains the same accepted assertion challenge, not any other test.
+    const acceptedChallenges = new Set(native.filter(o => o.outcome === 'ACCEPTED').map(o => o.challengeId))
+    const effectOutcome = effects.some(o => o.outcome === 'EXECUTED') ? 'EXECUTED' :
+      effects.some(o => o.outcome === 'BLOCKED' && acceptedChallenges.has(o.challengeId)) ? 'BLOCKED' : 'UNKNOWN'
+    let verdict = 'UNKNOWN'
+    if (effectOutcome === 'EXECUTED') verdict = 'UNPROTECTED_EFFECT'
+    else if (nativeOutcome === 'ACCEPTED' && effectOutcome === 'BLOCKED') verdict = 'RESIDUAL_TRUST_BLOCKED_AT_EFFECT'
+    else if (nativeOutcome === 'ACCEPTED') verdict = 'NATIVE_ACCEPTANCE_UNCONTROLLED'
+    else if (nativeOutcome === 'REJECTED') verdict = 'NATIVE_REJECTED'
+    return {
+      relyingPartyId, nativeOutcome, effectOutcome, verdict,
+      evidenceChallengeIds: [...new Set(party.map(o => o.challengeId))].sort()
+    }
+  })
+  return {
+    evidenceState: 'SIGNED_OBSERVATION_ASSESSMENT_NOT_NATIVE_SAML_CERTIFICATION',
+    issuerId, keyFingerprint, runId, knownRelyingParties: edges.length,
+    verifiedObservations: verified.length,
+    rejectedObservations: observations.length - verified.length,
+    allKnownPartiesNativeReject: edges.every(e => e.verdict === 'NATIVE_REJECTED'),
+    allKnownPartiesEffectConstrained: edges.every(e => ['NATIVE_REJECTED', 'RESIDUAL_TRUST_BLOCKED_AT_EFFECT'].includes(e.verdict)),
+    edges
+  }
+}
diff --git a/packages/trust-routing-engine/tests/retired-key-assurance.test.mjs b/packages/trust-routing-engine/tests/retired-key-assurance.test.mjs
new file mode 100644
index 0000000..53a6d7b
--- /dev/null
+++ b/packages/trust-routing-engine/tests/retired-key-assurance.test.mjs
@@ -0,0 +1,139 @@
+import test from 'node:test'
+import assert from 'node:assert/strict'
+import { createHash, generateKeyPairSync, sign, verify } from 'node:crypto'
+import { assessRetiredKeyCoverage, canonicalObservation } from '../src/retired-key-assurance.js'
+import { resolveTrustRoute, computeBindingHash } from '../src/resolve.js'
+
+// Synthetic protocol-level payloads, not SAML XML signatures or a live SP.
+// An SP's decision is established by verifying real RSA signatures against the
+// public key(s) the controlled test-SP is configured to trust.
+const key1 = generateKeyPairSync('rsa', { modulusLength: 2048 })
+const key2 = generateKeyPairSync('rsa', { modulusLength: 2048 })
+const observer = generateKeyPairSync('ed25519')
+const publicKeyPEM = observer.publicKey.export({ type: 'spki', format: 'pem' })
+const fingerprint = createHash('sha256').update(key1.publicKey.export({ type: 'spki', format: 'der' })).digest('hex')
+const issuerId = 'synthetic-idp-1'
+const runId = 'cfav-issue-90-local-fixture'
+const assessedAt = '2026-11-11T15:00:00.000Z'
+const scopes = { issuerId, keyFingerprint: fingerprint, runId,
+  relyingPartyIds: ['SP-A-DYNAMIC', 'SP-B-PINNED', 'SP-C-UNKNOWN'],
+  pinnedObserverKeys: { 'staging-observer-1': publicKeyPEM }, assessedAt }
+
+function assertion(privateKey, audience) {
+  const payload = { issuerId, audience, subject: 'synthetic-user',
+    issuedAt: '2026-11-11T14:59:00.000Z', expiresAt: '2026-11-11T15:04:00.000Z', nonce: 'synthetic-unique-1' }
+  const bytes = Buffer.from(JSON.stringify(payload))
+  return { payload, bytes, signature: sign('RSA-SHA256', bytes, privateKey) }
+}
+function targetAccepts(signed, audience, trustedPublicKeys) {
+  if (signed.payload.issuerId !== issuerId || signed.payload.audience !== audience) return false
+  if (Date.parse(signed.payload.expiresAt) <= Date.parse(assessedAt)) return false
+  return trustedPublicKeys.some(key => verify('RSA-SHA256', signed.bytes, key, signed.signature))
+}
+function observed(relyingPartyId, kind, outcome, challengeId) {
+  const o = { runId, observerId: 'staging-observer-1', issuerId, relyingPartyId,
+    keyFingerprint: fingerprint, challengeId, kind, outcome, observedAt: assessedAt }
+  return { ...o, signature: sign(null, canonicalObservation(o), observer.privateKey).toString('base64') }
+}
+function evaluate(observations) {
+  return assessRetiredKeyCoverage({ ...scopes, observations })
+}
+function protectedRouteDecision() {
+  const request = { subject: 'synthetic-user', action: 'record.write', resource: 'sp-b:protected-record',
+    paramsHash: 'sha256:synthetic', timestamp: assessedAt, context: {}, delegationHopCount: 0 }
+  request.bindingHash = computeBindingHash({ subject: request.subject, action: request.action,
+    resource: request.resource, paramsHash: request.paramsHash, timestampBucket: assessedAt.slice(0, 16) })
+  return resolveTrustRoute({ request, candidates: [{ issuerType: 'workload', issuerId,
+    proofRef: 'synthetic-proof', trustScore: 0.99, lastVerifiedAt: assessedAt,
+    freshnessSeconds: 0, revoked: true, action: 'record.write',
+    delegationAllowed: false, maxHops: 0, grantId: 'synthetic-grant', minTrustScore: 0.65 }] })
+}
+
+test('real RSA signatures: dynamic SP rejects retired K1, pinned SP accepts K1', () => {
+  const oldForA = assertion(key1.privateKey, 'SP-A-DYNAMIC')
+  const newForA = assertion(key2.privateKey, 'SP-A-DYNAMIC')
+  const oldForB = assertion(key1.privateKey, 'SP-B-PINNED')
+  assert.equal(targetAccepts(oldForA, 'SP-A-DYNAMIC', [key2.publicKey]), false)
+  assert.equal(targetAccepts(newForA, 'SP-A-DYNAMIC', [key2.publicKey]), true)
+  assert.equal(targetAccepts(oldForB, 'SP-B-PINNED', [key1.publicKey]), true)
+  assert.equal(targetAccepts(oldForB, 'SP-A-DYNAMIC', [key1.publicKey]), false)
+})
+
+test('retired key is denied for protected effect despite pinned SP accepting it', () => {
+  const oldForB = assertion(key1.privateKey, 'SP-B-PINNED')
+  assert.equal(targetAccepts(oldForB, 'SP-B-PINNED', [key1.publicKey]), true)
+  const d = protectedRouteDecision()
+  assert.equal(d.decision, 'DENY')
+  assert.deepEqual(d.reasonCodes, ['revoked_subject'])
+  let protectedEffectOccurred = false
+  if (d.decision === 'PERMIT') protectedEffectOccurred = true
+  assert.equal(protectedEffectOccurred, false)
+  const report = evaluate([
+    observed('SP-A-DYNAMIC', 'native_assertion', 'REJECTED', 'A3'),
+    observed('SP-B-PINNED', 'native_assertion', 'ACCEPTED', 'A4'),
+    observed('SP-B-PINNED', 'protected_effect', 'BLOCKED', 'A4')
+  ])
+  assert.equal(report.allKnownPartiesNativeReject, false)
+  assert.equal(report.allKnownPartiesEffectConstrained, false) // SP-C still unknown
+  assert.equal(report.edges[0].verdict, 'NATIVE_REJECTED')
+  assert.equal(report.edges[1].verdict, 'RESIDUAL_TRUST_BLOCKED_AT_EFFECT')
+  assert.equal(report.edges[2].verdict, 'UNKNOWN')
+})
+
+test('a blocked effect from an unrelated challenge cannot establish protection', () => {
+  const report = evaluate([
+    observed('SP-B-PINNED', 'native_assertion', 'ACCEPTED', 'A4'),
+    observed('SP-B-PINNED', 'protected_effect', 'BLOCKED', 'different-challenge')
+  ])
+  assert.equal(report.edges[1].verdict, 'NATIVE_ACCEPTANCE_UNCONTROLLED')
+})
+
+test('accepted native assertion without observed downstream block is uncontrolled', () => {
+  const report = evaluate([observed('SP-B-PINNED', 'native_assertion', 'ACCEPTED', 'A4')])
+  assert.equal(report.edges[1].verdict, 'NATIVE_ACCEPTANCE_UNCONTROLLED')
+})
+
+test('confirmed protected effect after K1 retirement is critical counterexample', () => {
+  const report = evaluate([
+    observed('SP-B-PINNED', 'native_assertion', 'ACCEPTED', 'A4'),
+    observed('SP-B-PINNED', 'protected_effect', 'EXECUTED', 'A6')
+  ])
+  assert.equal(report.edges[1].verdict, 'UNPROTECTED_EFFECT')
+})
+
+test('forged and mutated observation cannot advance evidence state', () => {
+  const valid = observed('SP-A-DYNAMIC', 'native_assertion', 'REJECTED', 'A3')
+  const report = evaluate([{ ...valid, outcome: 'ACCEPTED' }, { ...valid, signature: 'AAAA' }])
+  assert.equal(report.verifiedObservations, 0)
+  assert.equal(report.rejectedObservations, 2)
+  assert.equal(report.edges[0].verdict, 'UNKNOWN')
+})
+
+test('different issuer, run, party, key or stale observation are not accepted', () => {
+  const valid = observed('SP-A-DYNAMIC', 'native_assertion', 'REJECTED', 'A3')
+  const old = { ...valid, observedAt: '2026-11-10T15:00:00.000Z' }
+  old.signature = sign(null, canonicalObservation(old), observer.privateKey).toString('base64')
+  const report = evaluate([
+    observed('SP-A-DYNAMIC', 'native_assertion', 'REJECTED', 'A3'),
+    observed('SP-X-NOT-IN-INVENTORY', 'native_assertion', 'REJECTED', 'bad-party'),
+    { ...valid, issuerId: 'other-issuer' },
+    { ...valid, runId: 'other-run' },
+    { ...valid, keyFingerprint: '0'.repeat(64) },
+    old
+  ])
+  assert.equal(report.verifiedObservations, 1) // un-inventoried SP observations cannot inflate verified coverage
+  assert.equal(report.rejectedObservations, 5)
+  assert.equal(report.knownRelyingParties, 3)
+  assert.equal(report.edges[0].verdict, 'NATIVE_REJECTED')
+})
+
+test('absence of known relying-party inventory never passes', () => {
+  assert.throws(() => assessRetiredKeyCoverage({ ...scopes, relyingPartyIds: [] }), /invalid_relying_party_inventory/)
+  assert.throws(() => assessRetiredKeyCoverage({ ...scopes, relyingPartyIds: ['SP-A-DYNAMIC', 'SP-A-DYNAMIC'] }), /invalid_relying_party_inventory/)
+})
+
+test('observer key must be pinned by host, not supplied by observation', () => {
+  const report = assessRetiredKeyCoverage({ ...scopes, pinnedObserverKeys: {},
+    observations: [observed('SP-A-DYNAMIC', 'native_assertion', 'REJECTED', 'A3')] })
+  assert.equal(report.edges[0].verdict, 'UNKNOWN')
+})