diff --git a/src/app/application-support.ts b/src/app/application-support.ts
index 1eb5a8bc..833e3f04 100644
--- a/src/app/application-support.ts
+++ b/src/app/application-support.ts
@@ -25,7 +25,7 @@ import {
   DEFAULT_CANCEL_REASON,
   shutdownRequestDigest,
 } from './operation-ledger.js'
-import { safeProviderDiagnostic } from './provider-values.js'
+import { runtimeFailureDiagnostic, safeProviderDiagnostic } from './provider-values.js'
 import { RUN_EFFECT_KIND, runEffectRequest } from './run-admission.js'
 import { executeRun } from './run-execution.js'
 import type { RunExecutionSnapshot } from './run-execution-snapshot.js'
@@ -363,7 +363,7 @@ async function reconcileSnapshot(
       usage: snapshot.usage ?? usageSnapshotForRun(current),
       ...(snapshot.error === undefined
         ? {}
-        : { error: safeProviderDiagnostic(snapshot.error, 'RUNTIME_RECONCILIATION_ERROR') }),
+        : { error: runtimeFailureDiagnostic(snapshot.error, 'RUNTIME_RECONCILIATION_ERROR') }),
       ...(snapshot.detail === undefined
         ? {}
         : { reason: safeProviderDiagnostic(snapshot.detail, 'RUNTIME_RECONCILIATION_STATUS') }),
diff --git a/src/app/provider-values.ts b/src/app/provider-values.ts
index cd4fe29d..1fa5b0a6 100644
--- a/src/app/provider-values.ts
+++ b/src/app/provider-values.ts
@@ -1,4 +1,5 @@
 import { safeProviderDiagnostic } from '../domain/provider-values.js'
+import { providerHttpFailureDiagnostic } from '../domain/runtime-diagnostics.js'
 
 export {
   finiteNonNegativeNumber,
@@ -8,6 +9,11 @@ export {
   safePublicIdentifier,
 } from '../domain/provider-values.js'
 
+/** A runtime failure keeps its provider HTTP status and error code; other text falls back. */
+export function runtimeFailureDiagnostic(value: unknown, fallback: string): string {
+  return providerHttpFailureDiagnostic(value) ?? safeProviderDiagnostic(value, fallback)
+}
+
 function safeProperty(value: object, key: string): unknown {
   try {
     return Reflect.get(value, key)
diff --git a/src/app/run-event-mapper.ts b/src/app/run-event-mapper.ts
index cd98c9f1..47c9a4c4 100644
--- a/src/app/run-event-mapper.ts
+++ b/src/app/run-event-mapper.ts
@@ -15,7 +15,10 @@ import type {
 import type { ExecutionEnvironmentObservation } from '../domain/execution-observation.js'
 import { localInteractionId } from '../domain/interaction-identity.js'
 import { redactSensitiveText, redactStructuredValue } from '../domain/redaction.js'
-import { publicRuntimeDiagnostic } from '../domain/runtime-diagnostics.js'
+import {
+  providerHttpFailureDiagnostic,
+  publicRuntimeDiagnostic,
+} from '../domain/runtime-diagnostics.js'
 import type { BraidRuntimeEvent } from '../domain/runtime-events.js'
 import type { BraidMessagePart, RunStatus } from '../domain/state.js'
 import { isCanonicalIsoDateTime } from '../domain/text.js'
@@ -28,6 +31,7 @@ import {
 import {
   finiteNonNegativeNumber,
   optionalFiniteNonNegativeNumber,
+  runtimeFailureDiagnostic,
   safeDiagnostic,
   safeProviderDiagnostic,
   safePublicIdentifier,
@@ -414,7 +418,7 @@ export function providerEventFor(
       return {
         kind: 'run.error',
         runId,
-        message: safeProviderDiagnostic(event.message, 'RUNTIME_BACKEND_ERROR'),
+        message: runtimeFailureDiagnostic(event.message, 'RUNTIME_BACKEND_ERROR'),
         recoverable: event.recoverable,
         provider,
       }
@@ -430,7 +434,11 @@ export function providerEventFor(
         usage: usageFromMetadata(event.metadata),
         ...(event.error === undefined
           ? {}
-          : { error: safeDiagnostic(event.error.message, 'RUNTIME_FINAL_ERROR') }),
+          : {
+              error:
+                providerHttpFailureDiagnostic(event.error.message) ??
+                safeDiagnostic(event.error.message, 'RUNTIME_FINAL_ERROR'),
+            }),
         ...(event.reason === undefined
           ? {}
           : {
diff --git a/src/app/run-replay.ts b/src/app/run-replay.ts
index 51aa23bd..ab87a8cf 100644
--- a/src/app/run-replay.ts
+++ b/src/app/run-replay.ts
@@ -4,7 +4,7 @@ import type { ProviderRunSnapshot } from '../ports/execution.js'
 import type { ReconcileInput, ReconnectInput, ReplayPort } from './application-ports.js'
 import { AppError } from './errors.js'
 import { safeSnapshotDetail, safeSnapshotText, safeSnapshotUsage } from './provider-snapshot.js'
-import { safeRuntimeDiagnostic } from './provider-values.js'
+import { runtimeFailureDiagnostic, safeRuntimeDiagnostic } from './provider-values.js'
 import { retainedExecutionRecoveryContext } from './run-recovery-context.js'
 
 interface RecoveryReconnectInput extends ReconnectInput {
@@ -195,7 +195,7 @@ export async function reconcileRun(
         }),
         ...(snapshot.error === undefined
           ? {}
-          : { error: safeSnapshotDetail(snapshot.error, 'RUNTIME_RECONCILIATION_ERROR') }),
+          : { error: runtimeFailureDiagnostic(snapshot.error, 'RUNTIME_RECONCILIATION_ERROR') }),
         ...(snapshot.detail === undefined
           ? {}
           : { reason: safeSnapshotDetail(snapshot.detail, 'RUNTIME_RECONCILIATION_STATUS') }),
diff --git a/src/domain/provider-values.ts b/src/domain/provider-values.ts
index 8026d2f4..f89fcbd2 100644
--- a/src/domain/provider-values.ts
+++ b/src/domain/provider-values.ts
@@ -1,7 +1,7 @@
 import { redactSensitiveText } from './secret-sanitizer.js'
 import { containsUnsafeControlCharacter } from './text.js'
 
-const SENSITIVE_DIAGNOSTIC =
+export const SENSITIVE_DIAGNOSTIC =
   /(?:secret|password|passphrase|token|bearer|authorization|credential|private(?:[_-]?key)?|api[-_]?key|session(?:[_-]?key)?|access[_-]?key|client[_-]?secret|signature|signed[_-]?url|nonce)/iu
 const SAFE_DIAGNOSTIC = /^[A-Z][A-Z0-9._:-]{0,63}$/u
 const TYPED_PROVIDER_DIAGNOSTIC = /^[A-Z][A-Z0-9]*(?:[._][A-Z0-9]+)*$/u
diff --git a/src/domain/runtime-diagnostics.ts b/src/domain/runtime-diagnostics.ts
index 745c0baf..449c0aa5 100644
--- a/src/domain/runtime-diagnostics.ts
+++ b/src/domain/runtime-diagnostics.ts
@@ -1,3 +1,6 @@
+import { SENSITIVE_DIAGNOSTIC } from './provider-values.js'
+import { redactSensitiveText } from './secret-sanitizer.js'
+
 export const BRAID_SANDBOX_INTERACTION_UNSUPPORTED =
   'BRAID_SANDBOX_INTERACTION_UNSUPPORTED' as const
 export const BRAID_SANDBOX_CLEANUP_UNCONFIRMED = 'BRAID_SANDBOX_CLEANUP_UNCONFIRMED' as const
@@ -15,3 +18,55 @@ export function publicRuntimeDiagnostic(value: unknown): string | undefined {
   }
   return PUBLIC_RUNTIME_DIAGNOSTICS[value as keyof typeof PUBLIC_RUNTIME_DIAGNOSTICS]
 }
+
+// Runtime's Router executor reports a non-success upstream response as
+// `router <status>: <body prefix>`, either as the whole message or after a
+// `<context>: transport failed: ` prefix.
+const PROVIDER_HTTP_FAILURE = /(?:^|:\s)router ([45]\d{2}): ([^\n]*)/u
+const PROVIDER_ERROR_OBJECT = /"error"\s*:\s*\{([^{}]*)/u
+const providerErrorField = (name: string) =>
+  new RegExp(String.raw`"${name}"\s*:\s*"([A-Za-z][A-Za-z0-9_.-]{0,63})"`, 'u')
+const PROVIDER_ERROR_TYPE = providerErrorField('type')
+const PROVIDER_ERROR_CODE = providerErrorField('code')
+
+function providerFailureClass(status: number): string {
+  if (status === 401 || status === 403) return 'RUNTIME_PROVIDER_UNAUTHORIZED'
+  if (status === 402) return 'RUNTIME_PROVIDER_PAYMENT_REQUIRED'
+  if (status === 404) return 'RUNTIME_PROVIDER_NOT_FOUND'
+  if (status === 429) return 'RUNTIME_PROVIDER_RATE_LIMITED'
+  if (status >= 500) return 'RUNTIME_PROVIDER_UNAVAILABLE'
+  return 'RUNTIME_PROVIDER_REJECTED'
+}
+
+// A provider-declared token is public only when it cannot carry credential material.
+function providerToken(scope: string, field: RegExp): string | undefined {
+  const value = field.exec(scope)?.[1]
+  if (value === undefined || value === 'error') return undefined
+  if (SENSITIVE_DIAGNOSTIC.test(value) || redactSensitiveText(value) !== value) return undefined
+  return value
+}
+
+/**
+ * Classify a runtime failure message into a public diagnostic.
+ *
+ * Provider text is untrusted, so only the HTTP status and the provider's own
+ * error type and code tokens survive; the free-text body never reaches state.
+ * Returns undefined when the message does not carry a provider HTTP failure.
+ */
+export function providerHttpFailureDiagnostic(value: unknown): string | undefined {
+  if (typeof value !== 'string') return undefined
+  const match = PROVIDER_HTTP_FAILURE.exec(value)
+  if (match === null) return undefined
+  const status = Number(match[1])
+  const body = match[2] ?? ''
+  const scopes = [PROVIDER_ERROR_OBJECT.exec(body)?.[1], body].filter(
+    (scope): scope is string => scope !== undefined,
+  )
+  const token = (field: RegExp) =>
+    scopes.map((scope) => providerToken(scope, field)).find((found) => found !== undefined)
+  const tokens = [token(PROVIDER_ERROR_TYPE), token(PROVIDER_ERROR_CODE)]
+    .filter((found): found is string => found !== undefined)
+    .filter((found, index, all) => all.indexOf(found) === index)
+  const detail = tokens.length === 0 ? '' : ` (${tokens.join('/')})`
+  return `${providerFailureClass(status)}: provider returned HTTP ${status}${detail}`
+}
diff --git a/test/application.test.ts b/test/application.test.ts
index 98089608..f7036840 100644
--- a/test/application.test.ts
+++ b/test/application.test.ts
@@ -11,6 +11,7 @@ import { createBraidApplication, DETERMINISTIC_PROFILE } from '../src/app/compos
 import { cancelRequestDigest } from '../src/app/operation-ledger.js'
 import { effectRequestDigest } from '../src/app/effect-coordinator.js'
 import { MemoryJournal } from '../src/app/journal.js'
+import { providerEventFor } from '../src/app/run-event-mapper.js'
 import { createProfileRecord } from '../src/app/profiles.js'
 import {
   createInteractionRequest,
@@ -22,6 +23,7 @@ import type { ConnectionRecord } from '../src/domain/entities.js'
 import type { BraidEventEnvelope } from '../src/domain/events.js'
 import { createConnectionId } from '../src/domain/ids.js'
 import { assertBraidState } from '../src/domain/invariants.js'
+import { providerHttpFailureDiagnostic } from '../src/domain/runtime-diagnostics.js'
 import type { RuntimeEventEnvelope } from '../src/domain/runtime-events.js'
 import { FixedClock } from '../src/ports/clock.js'
 import type { JournalPort } from '../src/ports/effect-storage.js'
@@ -1280,6 +1282,114 @@ test('provider diagnostics and model metadata cannot persist credential material
   assert.equal(state.runs[0]?.outputTokens, 0)
 })
 
+test('a provider HTTP rejection surfaces its status and error code instead of RUNTIME_FINAL_ERROR', async () => {
+  const canary = 'sk-tan-never-persist-this-provider-key-value'
+  const journal = new MemoryJournal(new FixedClock())
+  const app = new BraidApplication({
+    profile: DETERMINISTIC_PROFILE,
+    execution: {
+      async *streamTurn(): AsyncIterable<RuntimeStreamEvent> {
+        yield {
+          type: 'final',
+          status: 'failed',
+          reason: 'failed',
+          text: '',
+          error: {
+            kind: 'backend',
+            message: `routerInlineExecutor: transport failed: router 401: {"error":{"message":"Invalid API key ${canary}","type":"authentication_error","code":"invalid_key"}}`,
+          },
+          task: { id: 'task-router-401', intent: 'router-401' },
+          timestamp: '2026-08-01T00:00:00.000Z',
+        }
+      },
+    },
+    clock: new FixedClock(),
+    ids: new SequenceIds(),
+    journal,
+    effectStorage: journal,
+  })
+
+  app.initialize('/workspace')
+  const state = await app.send({ operationId: 'op-router-401', text: 'hello' }).completion
+  assert.equal(
+    state.runs[0]?.error,
+    'RUNTIME_PROVIDER_UNAUTHORIZED: provider returned HTTP 401 (authentication_error/invalid_key)',
+  )
+  assert.equal(JSON.stringify({ state, events: app.events() }).includes(canary), false)
+})
+
+test('a backend error event keeps the provider HTTP rejection class', () => {
+  const event = providerEventFor(
+    'run-backend-401',
+    {
+      type: 'backend_error',
+      message: 'routerInlineExecutor: transport failed: router 403: {"error":{"code":"forbidden"}}',
+      recoverable: false,
+    } as RuntimeStreamEvent,
+    { eventId: 'backend-401', providerSequence: 1, receivedAt: '2026-08-01T00:00:00.000Z' },
+  )
+  assert.equal(event.kind, 'run.error')
+  assert.equal(
+    event.message,
+    'RUNTIME_PROVIDER_UNAUTHORIZED: provider returned HTTP 403 (forbidden)',
+  )
+})
+
+test('provider HTTP failure diagnostics keep only status and safe provider tokens', () => {
+  assert.equal(
+    providerHttpFailureDiagnostic(
+      'router 402: {"error":{"message":"Add funds","type":"insufficient_funds","code":"payment_required"}}',
+    ),
+    'RUNTIME_PROVIDER_PAYMENT_REQUIRED: provider returned HTTP 402 (insufficient_funds/payment_required)',
+  )
+  assert.equal(
+    providerHttpFailureDiagnostic('x: router 503: upstream unavailable'),
+    'RUNTIME_PROVIDER_UNAVAILABLE: provider returned HTTP 503',
+  )
+  assert.equal(
+    providerHttpFailureDiagnostic(
+      'router 429: {"error":{"type":"rate_limit_error","code":"rate_limit_error"}}',
+    ),
+    'RUNTIME_PROVIDER_RATE_LIMITED: provider returned HTTP 429 (rate_limit_error)',
+  )
+  assert.equal(
+    providerHttpFailureDiagnostic(
+      'router 400: {"error":{"type":"secret_abc","code":"model_not_found"}}',
+    ),
+    'RUNTIME_PROVIDER_REJECTED: provider returned HTTP 400 (model_not_found)',
+  )
+  assert.equal(
+    providerHttpFailureDiagnostic(
+      'router 401: {"type":"error","error":{"type":"authentication_error","message":"bad"}}',
+    ),
+    'RUNTIME_PROVIDER_UNAUTHORIZED: provider returned HTTP 401 (authentication_error)',
+  )
+  for (const secret of [
+    'sk-tan-abcdef0123456789abcdef0123',
+    'ghp_abcdefghijklmnopqrstuvwxyz0123',
+    `AKIA${'ABCDEFGHIJKLMNOP'}`,
+    'client_secret_value',
+  ]) {
+    assert.equal(
+      providerHttpFailureDiagnostic(
+        `router 400: {"error":{"type":"${secret}","code":"${secret}"}}`,
+      ),
+      'RUNTIME_PROVIDER_REJECTED: provider returned HTTP 400',
+    )
+  }
+  assert.equal(
+    providerHttpFailureDiagnostic('tool said the router 404: {"error":{"type":"fake"}}'),
+    undefined,
+  )
+  assert.equal(
+    providerHttpFailureDiagnostic('router 500: upstream\n{"error":{"type":"injected"}}'),
+    'RUNTIME_PROVIDER_UNAVAILABLE: provider returned HTTP 500',
+  )
+  assert.equal(providerHttpFailureDiagnostic('router 200: ok'), undefined)
+  assert.equal(providerHttpFailureDiagnostic('transport failed: fetch failed'), undefined)
+  assert.equal(providerHttpFailureDiagnostic(undefined), undefined)
+})
+
 test('provider diagnostic getters cannot break execution failure handling', () => {
   const hostile = new Proxy(
     {},