From 96b629165b500464949c5ebce9c8d091a99821dc Mon Sep 17 00:00:00 2001
From: RainbowBird <git@luoling.moe>
Date: Mon, 7 Sep 2026 00:08:47 +0800
Subject: [PATCH] fix(server): pass through final upstream errors (#2333)

Signed-off-by: RainbowBird <git@luoling.moe>
---
 .agents/skills/create-pr/SKILL.md             |   1 +
 AGENTS.md                                     |   1 +
 server/AGENTS.md                              |  10 +
 .../routes/openai/v1/http/response.test.ts    |  22 ++
 .../api/src/routes/openai/v1/http/response.ts |  20 ++
 .../v1/operations/chat-completions/index.ts   |  15 +-
 .../adapters/tts/dashscope-cosyvoice.test.ts  |  20 +-
 .../src/services/adapters/tts/index.test.ts   |  67 +++++--
 .../api/src/services/adapters/tts/types.ts    |  18 +-
 .../api/src/services/adapters/tts/unspeech.ts |   8 +-
 .../src/services/domain/llm-router/router.ts  | 189 ++++++++++++------
 .../domain/llm-router/tests/router.test.ts    | 166 +++++++++++----
 .../services/domain/openai-speech/index.ts    |  16 +-
 13 files changed, 417 insertions(+), 136 deletions(-)
 create mode 100644 server/apps/api/src/routes/openai/v1/http/response.test.ts

diff --git a/.agents/skills/create-pr/SKILL.md b/.agents/skills/create-pr/SKILL.md
index 068264d21..ac0e73a5e 100644
--- a/.agents/skills/create-pr/SKILL.md
+++ b/.agents/skills/create-pr/SKILL.md
@@ -15,6 +15,7 @@ Create a reviewable PR from the exact commits intended for publication.
 4. Publish the intended commits through the available GitHub/`gh` workflow.
 5. Compose the PR body with a concise summary, exact verification commands, and the required visual table.
 6. Create the PR, then open it and verify its title, base/head branches, body, and embedded images.
+7. Get the PR review threads, comments, and check status. If a comment identifies a confirmed error, fix it, run focused checks, push the update, reply with evidence, and resolve the thread.
 
 ## Visual Evidence Workflow
 
diff --git a/AGENTS.md b/AGENTS.md
index 7b140e33c..a318617e0 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -256,6 +256,7 @@ as a first language.
 ## PR / Workflow Tips
 
 - When asked to create, open, publish, or prepare a pull request, always use the repo-local `create-pr` skill. For user-visible changes it orchestrates `use-vishot` and the matching runtime variant, then uploads before/after screenshots as GitHub user assets in the PR body.
+- After you create a pull request, get its review threads, comments, and check status. If a review identifies a confirmed error, fix it, run focused checks, push the update, reply with evidence, and resolve the thread.
 - Rebase pulls; branch naming `username/feat/short-name`; clear commit messages (gitmoji is prohibited).
 - Summarize changes, how tested (commands), and follow-ups.
 - Improve legacy you touch; avoid one-off patterns.
diff --git a/server/AGENTS.md b/server/AGENTS.md
index 4e7ea17e5..3f3cd1984 100644
--- a/server/AGENTS.md
+++ b/server/AGENTS.md
@@ -9,3 +9,13 @@
 - Use `safeParse` if the caller branches on valid and invalid data.
 - Do not use `typeof`, `Record<string, unknown>`, or type casts as runtime input validation.
 - Infer TypeScript types from Valibot schemas. Do not duplicate the contract in an interface.
+
+## Architecture decisions
+
+- Put server ADRs in `../airi-docs/adr/`.
+- Create or update the ADR before you change a server boundary.
+- A server boundary includes an HTTP contract, provider contract, persistence model, or cross-module lifecycle.
+- Add a module dependency graph, an affected-file tree, and a sequence diagram to every implementation ADR.
+- State the decision, scope, non-goals, and test plan in the ADR.
+- Keep the ADR status `accepted` only after the decision is confirmed.
+- Update the ADR when implementation changes the accepted design.
diff --git a/server/apps/api/src/routes/openai/v1/http/response.test.ts b/server/apps/api/src/routes/openai/v1/http/response.test.ts
new file mode 100644
index 000000000..34c0f932e
--- /dev/null
+++ b/server/apps/api/src/routes/openai/v1/http/response.test.ts
@@ -0,0 +1,22 @@
+import { describe, expect, it } from 'vitest'
+
+import { buildSafeErrorResponseHeaders } from './response'
+
+describe('buildSafeErrorResponseHeaders', () => {
+  it('keeps the provider error content type and retry delay only', () => {
+    const headers = buildSafeErrorResponseHeaders(new Response('provider error', {
+      status: 429,
+      headers: {
+        'content-type': 'application/problem+json',
+        'retry-after': '30',
+        'set-cookie': 'provider-session=secret',
+        'x-request-id': 'provider-request-id',
+      },
+    }))
+
+    expect(headers.get('content-type')).toBe('application/problem+json')
+    expect(headers.get('retry-after')).toBe('30')
+    expect(headers.get('set-cookie')).toBeNull()
+    expect(headers.get('x-request-id')).toBeNull()
+  })
+})
diff --git a/server/apps/api/src/routes/openai/v1/http/response.ts b/server/apps/api/src/routes/openai/v1/http/response.ts
index 668a39f54..ffd357b3b 100644
--- a/server/apps/api/src/routes/openai/v1/http/response.ts
+++ b/server/apps/api/src/routes/openai/v1/http/response.ts
@@ -5,6 +5,11 @@ const SAFE_RESPONSE_HEADERS = new Set([
   'cache-control',
 ])
 
+const SAFE_ERROR_RESPONSE_HEADERS = new Set([
+  'content-type',
+  'retry-after',
+])
+
 export function buildSafeResponseHeaders(response: Response): Headers {
   const headers = new Headers()
   response.headers.forEach((value, key) => {
@@ -13,3 +18,18 @@ export function buildSafeResponseHeaders(response: Response): Headers {
   })
   return headers
 }
+
+/**
+ * Builds the headers for a final upstream error response.
+ *
+ * Upstream errors can expose useful body types and retry delays. Other
+ * upstream headers can contain credentials, cookies, or provider internals.
+ */
+export function buildSafeErrorResponseHeaders(response: Response): Headers {
+  const headers = new Headers()
+  response.headers.forEach((value, key) => {
+    if (SAFE_ERROR_RESPONSE_HEADERS.has(key.toLowerCase()))
+      headers.set(key, value)
+  })
+  return headers
+}
diff --git a/server/apps/api/src/routes/openai/v1/operations/chat-completions/index.ts b/server/apps/api/src/routes/openai/v1/operations/chat-completions/index.ts
index 38dffcce7..559df1dfa 100644
--- a/server/apps/api/src/routes/openai/v1/operations/chat-completions/index.ts
+++ b/server/apps/api/src/routes/openai/v1/operations/chat-completions/index.ts
@@ -9,7 +9,7 @@ import { useLogger } from '@guiiai/logg'
 import { extractUsageFromBody } from '../../../../../services/domain/billing/billing'
 import { createBadRequestError } from '../../../../../utils/error'
 import { nanoid } from '../../../../../utils/id'
-import { buildSafeResponseHeaders } from '../../http/response'
+import { buildSafeErrorResponseHeaders, buildSafeResponseHeaders } from '../../http/response'
 import { createOpenAiRouteBilling } from '../../middlewares/billing'
 import { createRouteTelemetry, newRouteContext } from '../../middlewares/telemetry'
 
@@ -143,7 +143,7 @@ export function chatCompletions(deps: V1RouteDeps): GatewayCallback<'chat.comple
 
       return new Response(response.body, {
         status: response.status,
-        headers: buildSafeResponseHeaders(response),
+        headers: buildSafeErrorResponseHeaders(response),
       })
     }
 
@@ -259,7 +259,8 @@ async function routeChatAliasCandidates(input: {
   routeCtx: ReturnType<typeof newRouteContext>
 }> {
   let lastError: unknown
-  for (const modelId of input.modelIds) {
+  for (let index = 0; index < input.modelIds.length; index += 1) {
+    const modelId = input.modelIds[index]
     const routeCtx = newRouteContext()
     try {
       const response = await input.deps.llmRouter.route({
@@ -268,7 +269,13 @@ async function routeChatAliasCandidates(input: {
         headers: {},
         abortSignal: input.abortSignal,
       }, routeCtx)
-      return { modelId, response, routeCtx }
+      if (response.ok || index === input.modelIds.length - 1)
+        return { modelId, response, routeCtx }
+
+      // The alias owns the next configured model candidate. Its non-2xx body
+      // cannot reach the client while a later candidate can still serve the
+      // request, so release it before the next route attempt.
+      await response.body?.cancel().catch(() => {})
     }
     catch (err) {
       if (input.abortSignal?.aborted)
diff --git a/server/apps/api/src/services/adapters/tts/dashscope-cosyvoice.test.ts b/server/apps/api/src/services/adapters/tts/dashscope-cosyvoice.test.ts
index 64e6929c9..c31529e8e 100644
--- a/server/apps/api/src/services/adapters/tts/dashscope-cosyvoice.test.ts
+++ b/server/apps/api/src/services/adapters/tts/dashscope-cosyvoice.test.ts
@@ -3,6 +3,7 @@ import { Buffer } from 'node:buffer'
 import { describe, expect, it, vi } from 'vitest'
 
 import { dashscopeCosyvoiceAdapter } from './dashscope-cosyvoice'
+import { TtsUpstreamResponseError } from './types'
 
 const UNSPEECH = 'http://unspeech.local:5933'
 const SPEECH_URL = `${UNSPEECH}/v1/audio/speech`
@@ -52,11 +53,12 @@ describe('dashscopeCosyvoiceAdapter', () => {
     expect(Array.from(out)).toEqual(Array.from(audioBytes))
   })
 
-  it('throws Error with .status when unspeech returns non-2xx (router walks to next key)', async () => {
+  it('throws TtsUpstreamResponseError when unspeech returns non-2xx', async () => {
     const fetchImpl = vi.fn().mockResolvedValueOnce(new Response('bad key', { status: 401 }))
 
-    await expect(
-      dashscopeCosyvoiceAdapter.send(
+    let caught: unknown
+    try {
+      await dashscopeCosyvoiceAdapter.send(
         { text: 'hi', voice: 'longxiaochun_v2' },
         {
           keyPlaintext: Buffer.from('sk-test', 'utf8'),
@@ -65,8 +67,16 @@ describe('dashscopeCosyvoiceAdapter', () => {
           adapterParams: {},
           fetchImpl: fetchImpl as unknown as typeof fetch,
         },
-      ),
-    ).rejects.toMatchObject({ status: 401, message: expect.stringContaining('401') })
+      )
+    }
+    catch (error) {
+      caught = error
+    }
+
+    expect(caught).toBeInstanceOf(TtsUpstreamResponseError)
+    if (!(caught instanceof TtsUpstreamResponseError))
+      throw caught
+    expect(caught.response.status).toBe(401)
 
     expect(fetchImpl).toHaveBeenCalledTimes(1)
   })
diff --git a/server/apps/api/src/services/adapters/tts/index.test.ts b/server/apps/api/src/services/adapters/tts/index.test.ts
index 0d0aa59b0..3c4fbce37 100644
--- a/server/apps/api/src/services/adapters/tts/index.test.ts
+++ b/server/apps/api/src/services/adapters/tts/index.test.ts
@@ -4,6 +4,7 @@ import { describe, expect, it, vi } from 'vitest'
 
 import { ApiError } from '../../../utils/error'
 import { getAdapter } from './index'
+import { TtsUpstreamResponseError } from './types'
 
 describe('getAdapter', () => {
   it('returns the azure adapter by id', () => {
@@ -280,20 +281,31 @@ describe('azureAdapter.send', () => {
     expect(fetchImpl).not.toHaveBeenCalled()
   })
 
-  it('throws Error with .status when unspeech non-2xx', async () => {
+  it('throws TtsUpstreamResponseError when unspeech returns non-2xx', async () => {
     const adapter = getAdapter('azure')
     const fetchImpl = vi.fn(async () => new Response('upstream rejected', { status: 401 })) as unknown as typeof fetch
 
-    await expect(adapter.send(
-      { text: 'hi', voice: 'en-US-AvaMultilingualNeural' },
-      {
-        keyPlaintext: Buffer.from('k', 'utf8'),
-        baseURL: 'https://eastasia.tts.speech.microsoft.com/cognitiveservices/v1',
-        unspeechBaseURL: 'http://unspeech.local:5933',
-        adapterParams: { region: 'eastasia' },
-        fetchImpl,
-      },
-    )).rejects.toMatchObject({ status: 401 })
+    let caught: unknown
+    try {
+      await adapter.send(
+        { text: 'hi', voice: 'en-US-AvaMultilingualNeural' },
+        {
+          keyPlaintext: Buffer.from('k', 'utf8'),
+          baseURL: 'https://eastasia.tts.speech.microsoft.com/cognitiveservices/v1',
+          unspeechBaseURL: 'http://unspeech.local:5933',
+          adapterParams: { region: 'eastasia' },
+          fetchImpl,
+        },
+      )
+    }
+    catch (error) {
+      caught = error
+    }
+
+    expect(caught).toBeInstanceOf(TtsUpstreamResponseError)
+    if (!(caught instanceof TtsUpstreamResponseError))
+      throw caught
+    expect(caught.response.status).toBe(401)
   })
 })
 
@@ -459,20 +471,31 @@ describe('stepfunAdapter', () => {
     expect(body.extra_body.voice_label).toEqual({ emotion: '高兴' })
   })
 
-  it('throws Error with .status when unspeech returns non-2xx', async () => {
+  it('throws TtsUpstreamResponseError when unspeech returns non-2xx', async () => {
     const adapter = getAdapter('stepfun')
     const fetchImpl = vi.fn(async () => new Response('bad key', { status: 401 })) as unknown as typeof fetch
 
-    await expect(adapter.send(
-      { text: 'hi', voice: 'cixingnansheng' },
-      {
-        keyPlaintext: Buffer.from('bad-key', 'utf8'),
-        baseURL: 'https://api.stepfun.com',
-        unspeechBaseURL: 'http://unspeech.local',
-        adapterParams: { model: 'stepaudio-2.5-tts' },
-        fetchImpl,
-      },
-    )).rejects.toMatchObject({ status: 401 })
+    let caught: unknown
+    try {
+      await adapter.send(
+        { text: 'hi', voice: 'cixingnansheng' },
+        {
+          keyPlaintext: Buffer.from('bad-key', 'utf8'),
+          baseURL: 'https://api.stepfun.com',
+          unspeechBaseURL: 'http://unspeech.local',
+          adapterParams: { model: 'stepaudio-2.5-tts' },
+          fetchImpl,
+        },
+      )
+    }
+    catch (error) {
+      caught = error
+    }
+
+    expect(caught).toBeInstanceOf(TtsUpstreamResponseError)
+    if (!(caught instanceof TtsUpstreamResponseError))
+      throw caught
+    expect(caught.response.status).toBe(401)
   })
 
   it('preserves an unspeech request abort for router timeout classification', async () => {
diff --git a/server/apps/api/src/services/adapters/tts/types.ts b/server/apps/api/src/services/adapters/tts/types.ts
index 1c52ef44c..81f36a902 100644
--- a/server/apps/api/src/services/adapters/tts/types.ts
+++ b/server/apps/api/src/services/adapters/tts/types.ts
@@ -70,6 +70,19 @@ export interface TtsResult {
   body: ArrayBuffer | ReadableStream<Uint8Array>
 }
 
+/**
+ * A non-2xx response from the immediate TTS upstream.
+ *
+ * The router uses this response for configured fallback. It returns the final
+ * response to the client when every permitted fallback has failed.
+ */
+export class TtsUpstreamResponseError extends Error {
+  constructor(readonly response: Response) {
+    super(`TTS upstream responded with ${response.status}`)
+    this.name = 'TtsUpstreamResponseError'
+  }
+}
+
 /**
  * Stable provider identifier for the v1 adapter registry.
  *
@@ -120,9 +133,8 @@ export interface TtsVoiceCatalogContext {
  *
  * Returns:
  * - A {@link TtsResult} on 2xx upstream responses.
- * - Throws (Error subclass) on upstream non-2xx — the router maps the error to
- *   the next fallback key/upstream or to a 5xx for the caller. Adapters MUST
- *   NOT swallow upstream failures.
+ * - Throws {@link TtsUpstreamResponseError} on upstream non-2xx. The router
+ *   can use the response for a fallback or return it to the caller.
  */
 export interface TtsAdapter {
   /** Stable id used by the registry and config (`tts.upstreams[i].adapter`). */
diff --git a/server/apps/api/src/services/adapters/tts/unspeech.ts b/server/apps/api/src/services/adapters/tts/unspeech.ts
index 9d8117262..f7f631ce6 100644
--- a/server/apps/api/src/services/adapters/tts/unspeech.ts
+++ b/server/apps/api/src/services/adapters/tts/unspeech.ts
@@ -6,6 +6,7 @@ import { errorMessageFrom } from '@moeru/std'
 import { generateSpeechResponse, listVoices, UnSpeechAPIError } from 'unspeech'
 
 import { createBadGatewayError, createInternalError } from '../../../utils/error'
+import { TtsUpstreamResponseError } from './types'
 
 interface SendSpeechOptions {
   ctx: TtsAdapterContext
@@ -72,9 +73,10 @@ export async function sendSpeechViaUnSpeech(options: SendSpeechOptions): Promise
       throw error
 
     if (error instanceof UnSpeechAPIError) {
-      const err = new Error(`${providerLabel} tts upstream ${error.status}: ${error.responseBody.slice(0, 256)}`) as Error & { status?: number }
-      err.status = error.status
-      throw err
+      throw new TtsUpstreamResponseError(new Response(error.responseBody, {
+        status: error.status,
+        headers: error.responseHeaders,
+      }))
     }
 
     throw createInternalError(`${providerLabel} tts fetch failed: ${errorMessageFrom(error) ?? 'unknown'}`)
diff --git a/server/apps/api/src/services/domain/llm-router/router.ts b/server/apps/api/src/services/domain/llm-router/router.ts
index 96461015b..df84ab99f 100644
--- a/server/apps/api/src/services/domain/llm-router/router.ts
+++ b/server/apps/api/src/services/domain/llm-router/router.ts
@@ -8,6 +8,7 @@ import type { EnvelopeCrypto } from '../../../utils/envelope-crypto'
 import type { ConfigKVService } from '../../adapters/config-kv'
 import type { TtsAdapterId, TtsInput } from '../../adapters/tts/types'
 import type { ConcurrencyLedger } from './concurrency-ledger'
+import type { UpstreamAttempt } from './error-mapping'
 import type { LlmRouteContext, LlmRouteRequest, LlmRoutingGroup, LlmUpstream, RouteFailureTriggers, TtsRoutingGroup, TtsUpstream } from './types'
 
 import { Buffer as NodeBuffer } from 'node:buffer'
@@ -24,12 +25,29 @@ import {
   AIRI_ATTR_GEN_AI_GATEWAY_UPSTREAM_URL,
 } from '../../../utils/observability'
 import { getAdapter } from '../../adapters/tts'
+import { TtsUpstreamResponseError } from '../../adapters/tts/types'
 import { createConfigLoader } from './config-loader'
 import { mapUpstreamError } from './error-mapping'
 import { createKeyRotator } from './key-rotator'
 
 const UPSTREAM_BODY_SNIPPET_MAX = 256
 
+interface HttpAttemptFailure {
+  keyId: string
+  status: number | 'timeout'
+  bodySnippet?: string
+  errorMessage?: string
+  response?: Response
+}
+
+function toDiagnosticAttempt({ provider, keyId, status, bodySnippet, errorMessage }: HttpAttemptFailure & { provider: string }): UpstreamAttempt {
+  return { provider, keyId, status, bodySnippet, errorMessage }
+}
+
+async function discardUpstreamResponse(response: Response | undefined): Promise<void> {
+  await response?.body?.cancel().catch(() => {})
+}
+
 /**
  * Read at most `maxBytes` from an upstream non-2xx response body for
  * diagnostic logging, then cancel the rest so the socket can return to
@@ -214,8 +232,8 @@ function ttsVoicesCacheKey(provider: string, modelName: string): string {
  * Returns:
  * - `route(req)` — picks an upstream + key, fetches the upstream, walks
  *   fallback on non-2xx until one succeeds or every (upstream, key) has
- *   been tried. Returns a `Response` on the first 2xx; throws `ApiError`
- *   per KTD-1 mapping on full exhaustion.
+ *   been tried. Returns a `Response` on the first 2xx or terminal upstream
+ *   HTTP error. Throws `ApiError` when every attempt fails before a response.
  *
  * The router does NOT open its own OTel span — the route handler in U4
  * owns the span. The router only enriches the *active* span with
@@ -243,15 +261,15 @@ export function createLlmRouterService(options: CreateLlmRouterServiceOptions) {
     req: LlmRouteRequest,
     perAttemptTimeoutMs: number,
     fallbackHttpCodes: number[],
-    onAttemptFailure: (failure: { keyId: string, status: number | 'timeout', bodySnippet?: string, errorMessage?: string }) => void,
+    onAttemptFailure: (failure: HttpAttemptFailure) => void,
   ): Promise<
     | { kind: 'ok', response: Response, attemptIndex: number, upstreamModel: string }
-    | { kind: 'exhausted', failures: Array<{ keyId: string, status: number | 'timeout', bodySnippet?: string, errorMessage?: string }> }
+    | { kind: 'exhausted', failures: HttpAttemptFailure[] }
   > {
     const provider = deriveProviderTag(upstream.baseURL)
     const rotator = createKeyRotator(upstream, options.envelopeCrypto, req.modelName, options.gatewayMetrics, provider)
 
-    const failures: Array<{ keyId: string, status: number | 'timeout', bodySnippet?: string, errorMessage?: string }> = []
+    const failures: HttpAttemptFailure[] = []
     let attemptIndex = 0
 
     for (const key of rotator) {
@@ -299,6 +317,7 @@ export function createLlmRouterService(options: CreateLlmRouterServiceOptions) {
         }
 
         if (response.ok) {
+          await Promise.all(failures.map(failure => discardUpstreamResponse(failure.response)))
           // First 2xx wins. Enrich the active span and return.
           trace.getActiveSpan()?.setAttributes({
             [AIRI_ATTR_GEN_AI_GATEWAY_UPSTREAM_URL]: upstream.baseURL,
@@ -311,17 +330,15 @@ export function createLlmRouterService(options: CreateLlmRouterServiceOptions) {
 
         const status = response.status
         // NOTICE:
-        // Drain at most UPSTREAM_BODY_SNIPPET_MAX bytes of the failed body
-        // for diagnostic logging (operators need to see the upstream's real
-        // error, not just the status code), then cancel the rest so the
-        // socket can return to the pool. Without the cancel, a 401/429/5xx
-        // fallback storm leaves half-read bodies in flight and exhausts the
-        // connection pool exactly when the upstream is sick.
+        // Read a cloned response for diagnostic logging. The original response
+        // stays unread because it can become the final client response. When a
+        // later fallback wins, this router cancels the discarded response.
         // Source: codex review 2026-05-15 HIGH #2 (cancel) + cause-propagation
         // follow-up 2026-05-16 (snippet).
-        const bodySnippet = await readUpstreamBodySnippet(response)
-        failures.push({ keyId: key.id, status, bodySnippet })
-        onAttemptFailure({ keyId: key.id, status, bodySnippet })
+        const bodySnippet = await readUpstreamBodySnippet(response.clone())
+        const failure = { keyId: key.id, status, bodySnippet, response }
+        failures.push(failure)
+        onAttemptFailure(failure)
         options.gatewayMetrics?.fallbackCount.add(1, {
           provider,
           from_key: key.id,
@@ -345,6 +362,7 @@ export function createLlmRouterService(options: CreateLlmRouterServiceOptions) {
         // timeout. The router does NOT fall back on caller-abort: there is
         // no longer a client waiting for a response.
         if (req.abortSignal?.aborted) {
+          await Promise.all(failures.map(failure => discardUpstreamResponse(failure.response)))
           logger.withError(err).withFields({ keyId: key.id }).debug('Caller aborted upstream fetch; propagating without fallback')
           throw err
         }
@@ -355,8 +373,9 @@ export function createLlmRouterService(options: CreateLlmRouterServiceOptions) {
         // ApiError.cause so operators can tell apart "DNS failed" from
         // "attempt-timeout" without re-running the request.
         const errorMessage = errorMessageFromUnknown(err)
-        failures.push({ keyId: key.id, status: 'timeout', errorMessage })
-        onAttemptFailure({ keyId: key.id, status: 'timeout', errorMessage })
+        const failure = { keyId: key.id, status: 'timeout' as const, errorMessage }
+        failures.push(failure)
+        onAttemptFailure(failure)
         options.gatewayMetrics?.fallbackCount.add(1, {
           provider,
           from_key: key.id,
@@ -372,6 +391,7 @@ export function createLlmRouterService(options: CreateLlmRouterServiceOptions) {
       attemptIndex += 1
     }
 
+    await Promise.all(failures.slice(0, -1).map(failure => discardUpstreamResponse(failure.response)))
     return { kind: 'exhausted', failures }
   }
 
@@ -392,8 +412,9 @@ export function createLlmRouterService(options: CreateLlmRouterServiceOptions) {
     const defaults = slice.defaults ?? { perAttemptTimeoutMs: 30000, fullChainTimeoutMs: 60000, fallbackHttpCodes: [401, 402, 403, 429, 500, 502, 503, 504] }
     const fallbackHttpCodes = llmModel.fallbackTriggers?.httpCodes ?? defaults.fallbackHttpCodes ?? [401, 402, 403, 429, 500, 502, 503, 504]
 
-    const allFailures: Array<{ provider: string, keyId: string, status: number | 'timeout', bodySnippet?: string, errorMessage?: string }> = []
+    const allFailures: Array<HttpAttemptFailure & { provider: string }> = []
     let triedUpstreams = 0
+    let terminalResponse: Response | undefined
 
     async function attemptUpstream(upstream: LlmUpstream, index: number) {
       const provider = deriveProviderTag(upstream.baseURL)
@@ -424,12 +445,13 @@ export function createLlmRouterService(options: CreateLlmRouterServiceOptions) {
       return {
         kind: 'exhausted' as const,
         statuses: result.failures.map(failure => failure.status),
+        response: result.failures.at(-1)?.response,
       }
     }
 
     async function routeGroup(group: LlmRoutingGroup): Promise<
       | { kind: 'ok', response: Response }
-      | { kind: 'exhausted', statuses: Array<number | 'timeout'>, transitionBlocked: boolean }
+      | { kind: 'exhausted', statuses: Array<number | 'timeout'>, transitionBlocked: boolean, response?: Response }
     > {
       const statuses: Array<number | 'timeout'> = []
       for (let groupCandidateIndex = 0; groupCandidateIndex < group.upstreamIds.length; groupCandidateIndex += 1) {
@@ -447,10 +469,12 @@ export function createLlmRouterService(options: CreateLlmRouterServiceOptions) {
         statuses.push(...result.statuses)
         const hasNextCandidate = groupCandidateIndex < group.upstreamIds.length - 1
         if (hasNextCandidate && !failuresMatch(result.statuses, group.retryOn))
-          return { kind: 'exhausted', statuses, transitionBlocked: true }
+          return { kind: 'exhausted', statuses, transitionBlocked: true, response: result.response }
+        if (hasNextCandidate)
+          await discardUpstreamResponse(result.response)
       }
 
-      return { kind: 'exhausted', statuses, transitionBlocked: false }
+      return { kind: 'exhausted', statuses, transitionBlocked: false, response: allFailures.at(-1)?.response }
     }
 
     if (llmModel.routing != null) {
@@ -466,8 +490,11 @@ export function createLlmRouterService(options: CreateLlmRouterServiceOptions) {
           || !hasNextGroup
           || !failuresMatch(result.statuses, group.continueOn)
         ) {
+          if (result.response != null)
+            terminalResponse = result.response
           break
         }
+        await discardUpstreamResponse(result.response)
       }
     }
     else {
@@ -475,6 +502,10 @@ export function createLlmRouterService(options: CreateLlmRouterServiceOptions) {
         const result = await attemptUpstream(llmModel.upstreams[index], index)
         if (result.kind === 'ok')
           return result.response
+        if (index < llmModel.upstreams.length - 1)
+          await discardUpstreamResponse(result.response)
+        else if (result.response != null)
+          terminalResponse = result.response
       }
     }
 
@@ -512,6 +543,9 @@ export function createLlmRouterService(options: CreateLlmRouterServiceOptions) {
       }
     }
 
+    if (terminalResponse != null)
+      return terminalResponse
+
     throw mapUpstreamError(
       lastFailure.status,
       {
@@ -519,15 +553,15 @@ export function createLlmRouterService(options: CreateLlmRouterServiceOptions) {
         triedUpstreams,
         lastStatusCode: lastFailure.status,
       },
-      allFailures,
+      allFailures.map(toDiagnosticAttempt),
     )
   }
 
   /**
    * Run one TTS upstream's key list in order, parallel to {@link dispatchOneUpstream}
    * but delegating actual HTTP to the provider adapter. Adapters surface
-   * upstream non-2xx as `Error & { status: number }`; network failures /
-   * timeouts arrive as plain `Error` with no status.
+   * upstream non-2xx as {@link TtsUpstreamResponseError}; network failures
+   * and timeouts arrive as errors without an upstream response.
    */
   async function dispatchOneTtsUpstream(
     upstream: TtsUpstream,
@@ -539,15 +573,15 @@ export function createLlmRouterService(options: CreateLlmRouterServiceOptions) {
     perAttemptTimeoutMs: number,
     fallbackHttpCodes: number[],
     unspeechBaseURL: string,
-    onAttemptFailure: (failure: { keyId: string, status: number | 'timeout', errorMessage?: string }) => void,
+    onAttemptFailure: (failure: HttpAttemptFailure) => void,
   ): Promise<
     | { kind: 'ok', contentType: string, body: ArrayBuffer | ReadableStream<Uint8Array>, attemptIndex: number }
-    | { kind: 'exhausted', failures: Array<{ keyId: string, status: number | 'timeout', errorMessage?: string }> }
+    | { kind: 'exhausted', failures: HttpAttemptFailure[] }
   > {
     const providerTag = deriveProviderTag(upstream.baseURL)
     const rotator = createKeyRotator(upstream, options.envelopeCrypto, modelName, options.gatewayMetrics, providerTag)
     const adapter = getAdapter(providerId)
-    const failures: Array<{ keyId: string, status: number | 'timeout', errorMessage?: string }> = []
+    const failures: HttpAttemptFailure[] = []
     let attemptIndex = 0
 
     for (const key of rotator) {
@@ -587,14 +621,38 @@ export function createLlmRouterService(options: CreateLlmRouterServiceOptions) {
           [AIRI_ATTR_GEN_AI_GATEWAY_KEY_ID]: key.id,
           [AIRI_ATTR_GEN_AI_GATEWAY_FALLBACK_DEPTH]: attemptIndex,
         })
+        await Promise.all(failures.map(failure => discardUpstreamResponse(failure.response)))
         return { kind: 'ok', contentType: result.contentType, body: result.body, attemptIndex }
       }
       catch (err) {
         if (abortSignal?.aborted) {
+          await Promise.all(failures.map(failure => discardUpstreamResponse(failure.response)))
           logger.withError(err).withFields({ keyId: key.id }).debug('Caller aborted upstream tts fetch; propagating without fallback')
           throw err
         }
 
+        if (err instanceof TtsUpstreamResponseError) {
+          const failure = { keyId: key.id, status: err.response.status, response: err.response }
+          failures.push(failure)
+          onAttemptFailure(failure)
+          options.gatewayMetrics?.fallbackCount.add(1, {
+            provider: providerTag,
+            from_key: key.id,
+            reason: String(failure.status),
+          })
+          options.gatewayMetrics?.upstreamErrors.add(1, {
+            provider: providerTag,
+            status_code: failure.status,
+          })
+          if (!fallbackHttpCodes.includes(failure.status)) {
+            attemptIndex += 1
+            break
+          }
+          logger.withError(err).withFields({ keyId: key.id, upstream: upstream.baseURL }).warn('Upstream TTS attempt failed')
+          attemptIndex += 1
+          continue
+        }
+
         // Adapter contract (see `server/apps/api/src/services/tts-adapters/types.ts`
         // and the three impls):
         //
@@ -613,34 +671,20 @@ export function createLlmRouterService(options: CreateLlmRouterServiceOptions) {
         if (err instanceof ApiError && err.statusCode < 500)
           throw err
 
-        const rawStatus
-          = (err as { status?: unknown }).status
-            ?? (err instanceof ApiError ? err.statusCode : undefined)
-        const failureStatus: number | 'timeout' = typeof rawStatus === 'number' ? rawStatus : 'timeout'
-        // TTS adapters bake the upstream body snippet into err.message
-        // (azure: `azure tts upstream 403: <body>`, cosyvoice / volcengine
-        // analogous), so a single errorMessage carries both the status
-        // and the upstream payload diagnostics.
+        const rawStatus = err instanceof ApiError ? err.statusCode : undefined
+        const failureStatus: number | 'timeout' = rawStatus ?? 'timeout'
         const errorMessage = errorMessageFromUnknown(err)
-        failures.push({ keyId: key.id, status: failureStatus, errorMessage })
-        onAttemptFailure({ keyId: key.id, status: failureStatus, errorMessage })
+        const failure = { keyId: key.id, status: failureStatus, errorMessage }
+        failures.push(failure)
+        onAttemptFailure(failure)
         options.gatewayMetrics?.fallbackCount.add(1, {
           provider: providerTag,
           from_key: key.id,
           reason: String(failureStatus),
         })
-        if (typeof rawStatus === 'number') {
-          options.gatewayMetrics?.upstreamErrors.add(1, {
-            provider: providerTag,
-            status_code: rawStatus,
-          })
-          if (!fallbackHttpCodes.includes(rawStatus)) {
-            // Same key-level policy as chat: stop rotating credentials in this
-            // candidate. The enclosing group separately decides whether another
-            // candidate may be tried.
-            attemptIndex += 1
-            break
-          }
+        if (typeof rawStatus === 'number' && !fallbackHttpCodes.includes(rawStatus)) {
+          attemptIndex += 1
+          break
         }
         logger.withError(err).withFields({ keyId: key.id, upstream: upstream.baseURL }).warn('Upstream TTS attempt failed')
       }
@@ -651,6 +695,7 @@ export function createLlmRouterService(options: CreateLlmRouterServiceOptions) {
       attemptIndex += 1
     }
 
+    await Promise.all(failures.slice(0, -1).map(failure => discardUpstreamResponse(failure.response)))
     return { kind: 'exhausted', failures }
   }
 
@@ -672,13 +717,13 @@ export function createLlmRouterService(options: CreateLlmRouterServiceOptions) {
     modelName: string,
     attemptUpstream: (upstream: TtsUpstream, index: number) => Promise<
       | { kind: 'ok', response: Response }
-      | { kind: 'exhausted', sawTooManyRequests: boolean, statuses: Array<number | 'timeout'> }
+      | { kind: 'exhausted', sawTooManyRequests: boolean, statuses: Array<number | 'timeout'>, response?: Response }
     >,
     retryOn?: RouteFailureTriggers,
     strategy: 'least-inflight' | 'ordered' = 'least-inflight',
   ): Promise<
     | { kind: 'ok', response: Response }
-    | { kind: 'exhausted', statuses: Array<number | 'timeout'>, transitionBlocked: boolean }
+    | { kind: 'exhausted', statuses: Array<number | 'timeout'>, transitionBlocked: boolean, response?: Response }
   > {
     async function markSaturated(upstream: TtsUpstream, poolId: string): Promise<void> {
       await ledger.markSaturated(poolId, ttsPoolSaturationTtlSeconds)
@@ -719,6 +764,13 @@ export function createLlmRouterService(options: CreateLlmRouterServiceOptions) {
     let dispatchedAny = false
     let attemptedPools = 0
     const statuses: Array<number | 'timeout'> = []
+    let lastResponse: Response | undefined
+
+    async function discardPreviousPoolResponse(): Promise<void> {
+      await discardUpstreamResponse(lastResponse)
+      lastResponse = undefined
+    }
+
     for (let rankedIndex = 0; rankedIndex < ranked.length; rankedIndex += 1) {
       const { upstream, index, poolId, maxConcurrency } = ranked[rankedIndex]
       const hasNextCandidate = rankedIndex < ranked.length - 1
@@ -726,14 +778,16 @@ export function createLlmRouterService(options: CreateLlmRouterServiceOptions) {
         // Unlimited pool — dispatch without occupying a slot.
         dispatchedAny = true
         attemptedPools += 1
+        await discardPreviousPoolResponse()
         const result = await attemptUpstream(upstream, index)
         if (result.kind === 'ok')
           return result
         statuses.push(...result.statuses)
+        lastResponse = result.response
         if (result.sawTooManyRequests)
           await markSaturated(upstream, poolId)
         if (hasNextCandidate && retryOn != null && !failuresMatch(result.statuses, retryOn))
-          return { kind: 'exhausted', statuses, transitionBlocked: true }
+          return { kind: 'exhausted', statuses, transitionBlocked: true, response: result.response }
         continue
       }
 
@@ -750,14 +804,16 @@ export function createLlmRouterService(options: CreateLlmRouterServiceOptions) {
       dispatchedAny = true
       attemptedPools += 1
       try {
+        await discardPreviousPoolResponse()
         const result = await attemptUpstream(upstream, index)
         if (result.kind === 'ok')
           return result
         statuses.push(...result.statuses)
+        lastResponse = result.response
         if (result.sawTooManyRequests)
           await markSaturated(upstream, poolId)
         if (hasNextCandidate && retryOn != null && !failuresMatch(result.statuses, retryOn))
-          return { kind: 'exhausted', statuses, transitionBlocked: true }
+          return { kind: 'exhausted', statuses, transitionBlocked: true, response: result.response }
       }
       finally {
         await ledger.release(poolId)
@@ -780,6 +836,7 @@ export function createLlmRouterService(options: CreateLlmRouterServiceOptions) {
       kind: 'exhausted',
       statuses,
       transitionBlocked: attemptedPools !== upstreams.length,
+      response: lastResponse,
     }
   }
 
@@ -804,8 +861,9 @@ export function createLlmRouterService(options: CreateLlmRouterServiceOptions) {
 
     const unspeechBaseURL = (await options.configKV.getOrThrow('UNSPEECH_UPSTREAM')).restBaseURL
 
-    const allFailures: Array<{ provider: string, keyId: string, status: number | 'timeout', errorMessage?: string }> = []
+    const allFailures: Array<HttpAttemptFailure & { provider: string }> = []
     let triedUpstreams = 0
+    let terminalResponse: Response | undefined
 
     // tts upstream schema has no per-upstream timeoutMs (see ttsUpstreamSchema);
     // the defaults bucket alone governs per-attempt timeout.
@@ -817,7 +875,7 @@ export function createLlmRouterService(options: CreateLlmRouterServiceOptions) {
     // so the caller can circuit-break thatpool.
     async function attemptUpstream(upstream: TtsUpstream, index: number): Promise<
       | { kind: 'ok', response: Response }
-      | { kind: 'exhausted', sawTooManyRequests: boolean, statuses: Array<number | 'timeout'> }
+      | { kind: 'exhausted', sawTooManyRequests: boolean, statuses: Array<number | 'timeout'>, response?: Response }
     > {
       const providerTag = deriveProviderTag(upstream.baseURL)
       triedUpstreams += 1
@@ -849,12 +907,13 @@ export function createLlmRouterService(options: CreateLlmRouterServiceOptions) {
         kind: 'exhausted',
         sawTooManyRequests: result.failures.some(f => f.status === 429),
         statuses: result.failures.map(failure => failure.status),
+        response: result.failures.at(-1)?.response,
       }
     }
 
     async function routeGroup(group: TtsRoutingGroup): Promise<
       | { kind: 'ok', response: Response }
-      | { kind: 'exhausted', statuses: Array<number | 'timeout'>, transitionBlocked: boolean }
+      | { kind: 'exhausted', statuses: Array<number | 'timeout'>, transitionBlocked: boolean, response?: Response }
     > {
       const indexedUpstreams = group.upstreamIds.map((upstreamId) => {
         const index = ttsModel.upstreams.findIndex(upstream => upstream.id === upstreamId)
@@ -892,10 +951,12 @@ export function createLlmRouterService(options: CreateLlmRouterServiceOptions) {
         statuses.push(...result.statuses)
         const hasNextCandidate = groupCandidateIndex < indexedUpstreams.length - 1
         if (hasNextCandidate && !failuresMatch(result.statuses, group.retryOn))
-          return { kind: 'exhausted', statuses, transitionBlocked: true }
+          return { kind: 'exhausted', statuses, transitionBlocked: true, response: result.response }
+        if (hasNextCandidate)
+          await discardUpstreamResponse(result.response)
       }
 
-      return { kind: 'exhausted', statuses, transitionBlocked: false }
+      return { kind: 'exhausted', statuses, transitionBlocked: false, response: allFailures.at(-1)?.response }
     }
 
     if (ttsModel.routing != null) {
@@ -911,8 +972,11 @@ export function createLlmRouterService(options: CreateLlmRouterServiceOptions) {
           || !hasNextGroup
           || !failuresMatch(result.statuses, group.continueOn)
         ) {
+          if (result.response != null)
+            terminalResponse = result.response
           break
         }
+        await discardUpstreamResponse(result.response)
       }
     }
     else {
@@ -925,12 +989,18 @@ export function createLlmRouterService(options: CreateLlmRouterServiceOptions) {
           const result = await attemptUpstream(ttsModel.upstreams[i], i)
           if (result.kind === 'ok')
             return result.response
+          if (i === ttsModel.upstreams.length - 1 && result.response != null)
+            terminalResponse = result.response
+          else
+            await discardUpstreamResponse(result.response)
         }
       }
       else {
         const result = await routeTtsAcrossPools(ttsModel.upstreams, req.modelName, attemptUpstream)
         if (result.kind === 'ok')
           return result.response
+        if (result.response != null)
+          terminalResponse = result.response
       }
     }
 
@@ -957,6 +1027,9 @@ export function createLlmRouterService(options: CreateLlmRouterServiceOptions) {
       }
     }
 
+    if (terminalResponse != null)
+      return terminalResponse
+
     throw mapUpstreamError(
       lastFailure.status,
       {
@@ -964,7 +1037,7 @@ export function createLlmRouterService(options: CreateLlmRouterServiceOptions) {
         triedUpstreams,
         lastStatusCode: lastFailure.status,
       },
-      allFailures,
+      allFailures.map(toDiagnosticAttempt),
     )
   }
 
diff --git a/server/apps/api/src/services/domain/llm-router/tests/router.test.ts b/server/apps/api/src/services/domain/llm-router/tests/router.test.ts
index 68eca3909..d7ee78618 100644
--- a/server/apps/api/src/services/domain/llm-router/tests/router.test.ts
+++ b/server/apps/api/src/services/domain/llm-router/tests/router.test.ts
@@ -281,10 +281,12 @@ describe('createLlmRouterService', () => {
     expect(ctx.upstreamModel).toBe('real/upstream-id')
   })
 
-  it('multi-key fallback: k1=401 then k2=200 → returns 200 and records fallbackCount once', async () => {
+  // https://github.com/moeru-ai/airi/pull/2333#discussion_r3820516102
+  it('pr #2333: multi-key fallback releases the failed chat response before returning success', async () => {
     const { config, crypto } = makeConfig({ upstreams: [{ baseURL: 'https://up-a.example/v1', keyIds: ['k1', 'k2'] }] })
+    const failedResponse = failResponse(401)
     const fetchImpl = vi.fn()
-      .mockResolvedValueOnce(failResponse(401))
+      .mockResolvedValueOnce(failedResponse)
       .mockResolvedValueOnce(happyResponse({ ok: 1 }))
     const metrics = makeMetrics()
 
@@ -299,6 +301,7 @@ describe('createLlmRouterService', () => {
 
     const res = await router.route({ modelName: 'openai/gpt-5-mini', body: {} })
     expect(res.status).toBe(200)
+    expect(failedResponse.bodyUsed).toBe(true)
     expect(fetchImpl.mock.calls.length).toBe(2)
 
     expect((metrics.fallbackCount.add as ReturnType<typeof vi.fn>).mock.calls.length).toBe(1)
@@ -310,6 +313,36 @@ describe('createLlmRouterService', () => {
     expect((metrics.keyExhaustedCount.add as ReturnType<typeof vi.fn>).mock.calls.length).toBe(0)
   })
 
+  // https://github.com/moeru-ai/airi/pull/2333#discussion_r3820516102
+  it('pr #2333: caller abort releases earlier failed chat responses', async () => {
+    const { config, crypto } = makeConfig({ upstreams: [{ baseURL: 'https://up-a.example/v1', keyIds: ['k1', 'k2'] }] })
+    const failedResponse = failResponse(401)
+    const callerAbort = new AbortController()
+    const fetchImpl = vi.fn()
+      .mockResolvedValueOnce(failedResponse)
+      .mockImplementationOnce(async () => {
+        callerAbort.abort(new Error('client disconnected'))
+        throw callerAbort.signal.reason
+      })
+
+    const router = createLlmRouterService({
+      configKV: makeConfigKV(config),
+      envelopeCrypto: crypto,
+      gatewayMetrics: null,
+      fetchImpl,
+      redis: makeRedisStub(),
+      concurrencyLedger: makeLedger(),
+    })
+
+    await expect(router.route({
+      modelName: 'openai/gpt-5-mini',
+      body: {},
+      abortSignal: callerAbort.signal,
+    })).rejects.toThrow('client disconnected')
+
+    expect(failedResponse.bodyUsed).toBe(true)
+  })
+
   it('cross-upstream fallback: upstream A keys all 401, upstream B[0] = 200 → returns 200 without terminal exhaustion', async () => {
     const { config, crypto } = makeConfig({
       upstreams: [
@@ -340,14 +373,20 @@ describe('createLlmRouterService', () => {
     expect((metrics.fallbackCount.add as ReturnType<typeof vi.fn>).mock.calls.length).toBe(2)
   })
 
-  it('full exhaustion: every upstream + every key 401 → throws 502 BAD_GATEWAY (KTD-1 last-cause = 401 → 502)', async () => {
+  it('full exhaustion: every upstream + every key 401 → returns the final upstream response', async () => {
     const { config, crypto } = makeConfig({
       upstreams: [
         { baseURL: 'https://up-a.example/v1', keyIds: ['kA1'] },
         { baseURL: 'https://up-b.example/v1', keyIds: ['kB1'] },
       ],
     })
-    const fetchImpl = vi.fn(async () => failResponse(401))
+    const fetchImpl = vi.fn(async () => new Response('provider denied', {
+      status: 401,
+      headers: {
+        'content-type': 'text/plain',
+        'retry-after': '30',
+      },
+    }))
     const metrics = makeMetrics()
 
     const router = createLlmRouterService({
@@ -359,16 +398,11 @@ describe('createLlmRouterService', () => {
       concurrencyLedger: makeLedger(),
     })
 
-    try {
-      await router.route({ modelName: 'openai/gpt-5-mini', body: {} })
-      throw new Error('expected throw')
-    }
-    catch (err) {
-      expect(err).toBeInstanceOf(ApiError)
-      expect((err as ApiError).statusCode).toBe(502)
-      expect((err as ApiError).errorCode).toBe('BAD_GATEWAY')
-      expect((err as ApiError).details).toMatchObject({ triedKeys: 2, triedUpstreams: 2, lastStatusCode: 401 })
-    }
+    const response = await router.route({ modelName: 'openai/gpt-5-mini', body: {} })
+    expect(response.status).toBe(401)
+    expect(response.headers.get('content-type')).toBe('text/plain')
+    expect(response.headers.get('retry-after')).toBe('30')
+    await expect(response.text()).resolves.toBe('provider denied')
 
     const exhaustionCalls = (metrics.keyExhaustedCount.add as ReturnType<typeof vi.fn>).mock.calls
     expect(exhaustionCalls.length).toBe(1)
@@ -431,6 +465,10 @@ describe('createLlmRouterService', () => {
       expect(first).toMatchObject({ keyId: 'kA1', status: 401 })
       expect(first.bodySnippet).toEqual(expect.stringContaining('key disabled'))
       expect(first.errorMessage).toBeUndefined()
+      // https://github.com/moeru-ai/airi/pull/2333#discussion_r3828016906
+      // `Response` owns headers and a body stream. The diagnostic cause must
+      // keep only the documented serializable attempt fields.
+      expect(first.response).toBeUndefined()
 
       const second = (cause!.attempts as Array<Record<string, unknown>>)[1]
       expect(second).toMatchObject({ keyId: 'kB1', status: 'timeout' })
@@ -439,7 +477,7 @@ describe('createLlmRouterService', () => {
     }
   })
 
-  it('same-status exhaustion: all keys 429 → throws 503 + sameStatusExhaustion incremented per provider', async () => {
+  it('same-status exhaustion: all keys 429 → returns 429 and increments sameStatusExhaustion per provider', async () => {
     const { config, crypto } = makeConfig({
       upstreams: [
         { baseURL: 'https://up-a.example/v1', keyIds: ['kA1', 'kA2'] },
@@ -458,7 +496,8 @@ describe('createLlmRouterService', () => {
       concurrencyLedger: makeLedger(),
     })
 
-    await expect(router.route({ modelName: 'openai/gpt-5-mini', body: {} })).rejects.toMatchObject({ statusCode: 503, errorCode: 'SERVICE_UNAVAILABLE' })
+    const response = await router.route({ modelName: 'openai/gpt-5-mini', body: {} })
+    expect(response.status).toBe(429)
 
     const calls = (metrics.sameStatusExhaustion.add as ReturnType<typeof vi.fn>).mock.calls
     expect(calls.length).toBe(2)
@@ -780,10 +819,11 @@ describe('createLlmRouterService', () => {
 
       const router = makeGroupedLlmRouter(fetchImpl)
 
-      await expect(router.route({
+      const response = await router.route({
         modelName: 'openai/gpt-5-mini',
         body: { messages: [] },
-      })).rejects.toBeInstanceOf(ApiError)
+      })
+      expect(response.status).toBe(429)
 
       expect(calledURLs).toEqual([
         'https://api.stepfun.com/step_plan/v1/chat/completions',
@@ -801,10 +841,11 @@ describe('createLlmRouterService', () => {
 
       const router = makeGroupedLlmRouter(fetchImpl)
 
-      await expect(router.route({
+      const response = await router.route({
         modelName: 'openai/gpt-5-mini',
         body: { messages: [] },
-      })).rejects.toBeInstanceOf(ApiError)
+      })
+      expect(response.status).toBe(401)
 
       expect(calledURLs).toEqual([
         'https://api.stepfun.com/step_plan/v1/chat/completions',
@@ -823,17 +864,19 @@ describe('createLlmRouterService', () => {
   // walked every key + upstream before surfacing — wasting upstream quota
   // and hiding the actual user-facing 400 behind a 502 mapping.
   //
-  // After patch: ApiError 4xx propagates immediately; ApiError 5xx folds
-  // into the network-failure fallback path using `statusCode`; `Error &
-  // { status }` stays on the existing fallback policy.
+  // After patch: ApiError 4xx propagates immediately. ApiError 5xx uses
+  // `statusCode` and obeys `fallbackHttpCodes`. TtsUpstreamResponseError
+  // stays on the existing fallback policy.
   describe('routeTts adapter error handling', () => {
     function makeTtsConfig(opts: {
       provider?: 'azure'
       upstreams?: Array<{ baseURL: string, keyIds: string[], adapterParams?: Record<string, unknown> }>
+      fallbackHttpCodes?: number[]
     }): { config: RouterConfig, crypto: ReturnType<typeof createEnvelopeCrypto> } {
       const crypto = createEnvelopeCrypto({ masterKey: freshMasterKey() })
       const modelName = 'tts-test'
       const upstreams = opts.upstreams ?? [{ baseURL: 'https://up-a.example', keyIds: ['kA1'] }]
+      const fallbackHttpCodes = opts.fallbackHttpCodes ?? [401, 429, 500, 502, 503, 504]
       const upstreamConfigs = upstreams.map(u => ({
         baseURL: u.baseURL,
         keys: u.keyIds.map((id) => {
@@ -850,14 +893,14 @@ describe('createLlmRouterService', () => {
             [modelName]: {
               provider: opts.provider ?? 'azure',
               upstreams: upstreamConfigs,
-              fallbackTriggers: { httpCodes: [401, 429, 500, 502, 503, 504], onTimeout: true },
+              fallbackTriggers: { httpCodes: fallbackHttpCodes, onTimeout: true },
             },
           },
         },
         defaults: {
           perAttemptTimeoutMs: 5000,
           fullChainTimeoutMs: 10000,
-          fallbackHttpCodes: [401, 429, 500, 502, 503, 504],
+          fallbackHttpCodes,
         },
       } as RouterConfig
       return { config, crypto }
@@ -936,17 +979,52 @@ describe('createLlmRouterService', () => {
       expect((metrics.fallbackCount.add as ReturnType<typeof vi.fn>).mock.calls.length).toBe(1)
     })
 
-    it('upstream `Error & { status: 401 }` folds into the existing fallback path', async () => {
-      // azure adapter throws `Error & { status: number }` on upstream non-2xx
-      // (see azure.ts:189-194). 401 is in fallbackHttpCodes so we must try
-      // the next key.
+    // https://github.com/moeru-ai/airi/pull/2333#discussion_r3820516115
+    it('pr #2333: apiError 5xx stops key fallback when fallbackHttpCodes excludes the status', async () => {
+      const { config, crypto } = makeTtsConfig({
+        upstreams: [{ baseURL: 'https://az.example', keyIds: ['kA1', 'kA2'], adapterParams: { region: 'eastasia' } }],
+        fallbackHttpCodes: [401, 429],
+      })
+      const fetchImpl = vi.fn(async () => {
+        throw new TypeError('network unreachable')
+      })
+
+      const router = createLlmRouterService({
+        configKV: makeConfigKV(config),
+        envelopeCrypto: crypto,
+        gatewayMetrics: null,
+        fetchImpl,
+        redis: makeRedisStub(),
+        concurrencyLedger: makeLedger(),
+      })
+
+      let caught: unknown
+      try {
+        await router.routeTts({
+          modelName: 'tts-test',
+          input: { text: 'hi', voice: 'en-US-AvaMultilingualNeural' },
+        })
+      }
+      catch (error) {
+        caught = error
+      }
+
+      expect(caught).toBeInstanceOf(ApiError)
+      expect((caught as ApiError).statusCode).toBe(502)
+      expect(fetchImpl).toHaveBeenCalledTimes(1)
+    })
+
+    it('upstream 401 folds into the existing fallback path', async () => {
+      // The Azure adapter throws TtsUpstreamResponseError on upstream non-2xx.
+      // 401 is in fallbackHttpCodes so we must try the next key.
       const { config, crypto } = makeTtsConfig({ upstreams: [{ baseURL: 'https://az.example', keyIds: ['kA1', 'kA2'], adapterParams: { region: 'eastasia' } }] })
 
       let callIdx = 0
+      const failedResponse = failResponse(401)
       const fetchImpl = vi.fn(async () => {
         callIdx += 1
         if (callIdx === 1)
-          return failResponse(401)
+          return failedResponse
         return new Response(new Uint8Array([0x01]), { status: 200, headers: { 'content-type': 'audio/mpeg' } })
       })
       const metrics = makeMetrics()
@@ -966,6 +1044,7 @@ describe('createLlmRouterService', () => {
       })
 
       expect(res.status).toBe(200)
+      expect(failedResponse.bodyUsed).toBe(true)
       expect(fetchImpl).toHaveBeenCalledTimes(2)
       const fallbackCalls = (metrics.fallbackCount.add as ReturnType<typeof vi.fn>).mock.calls
       expect(fallbackCalls.length).toBe(1)
@@ -995,10 +1074,12 @@ describe('createLlmRouterService', () => {
         concurrencyLedger: makeLedger(),
       })
 
-      await expect(router.routeTts({
+      const response = await router.routeTts({
         modelName: 'tts-test',
         input: { text: 'hi', voice: 'en-US-AvaMultilingualNeural' },
-      })).rejects.toMatchObject({ statusCode: 502 })
+      })
+      expect(response.status).toBe(451)
+      await expect(response.json()).resolves.toEqual({ error: 'bad' })
 
       const exhaustionCalls = (metrics.keyExhaustedCount.add as ReturnType<typeof vi.fn>).mock.calls
       expect(exhaustionCalls.length).toBe(1)
@@ -1323,10 +1404,11 @@ describe('createLlmRouterService', () => {
 
       const router = makeGroupedStepfunRouter(fetchImpl)
 
-      await expect(router.routeTts({
+      const response = await router.routeTts({
         modelName: 'stepfun/stepaudio-2.5-tts',
         input: { text: '你好' },
-      })).rejects.toBeInstanceOf(ApiError)
+      })
+      expect(response.status).toBe(429)
 
       expect(calledProfiles).toEqual(['step-plan', 'step-plan'])
       expect(calledProfiles).not.toContain('default')
@@ -1342,10 +1424,11 @@ describe('createLlmRouterService', () => {
 
       const router = makeGroupedStepfunRouter(fetchImpl)
 
-      await expect(router.routeTts({
+      const response = await router.routeTts({
         modelName: 'stepfun/stepaudio-2.5-tts',
         input: { text: '你好' },
-      })).rejects.toBeInstanceOf(ApiError)
+      })
+      expect(response.status).toBe(401)
 
       expect(calledProfiles).toEqual(['step-plan'])
     })
@@ -1638,10 +1721,11 @@ describe('createLlmRouterService', () => {
 
       const router = makePoolRouter(config, crypto, ledger, fetchImpl)
 
-      await expect(router.routeTts({
+      const response = await router.routeTts({
         modelName: 'tts-pool',
         input: { text: 'hi' },
-      })).rejects.toBeInstanceOf(ApiError)
+      })
+      expect(response.status).toBe(402)
 
       expect(selectedAppIds).toEqual(['plan-b'])
     })
@@ -1728,7 +1812,8 @@ describe('createLlmRouterService', () => {
       const fetchImpl = vi.fn(async () => failResponse(429)) as unknown as typeof fetch
 
       const router = makePoolRouter(config, crypto, ledger, fetchImpl)
-      await expect(router.routeTts({ modelName: 'tts-pool', input: { text: 'hi' } })).rejects.toBeInstanceOf(ApiError)
+      const response = await router.routeTts({ modelName: 'tts-pool', input: { text: 'hi' } })
+      expect(response.status).toBe(429)
 
       expect(markSaturated).toHaveBeenCalledWith('app-1', expect.any(Number))
     })
@@ -1743,7 +1828,8 @@ describe('createLlmRouterService', () => {
       const fetchImpl = vi.fn(async () => failResponse(500)) as unknown as typeof fetch
 
       const router = makePoolRouter(config, crypto, ledger, fetchImpl)
-      await expect(router.routeTts({ modelName: 'tts-pool', input: { text: 'hi' } })).rejects.toBeInstanceOf(ApiError)
+      const response = await router.routeTts({ modelName: 'tts-pool', input: { text: 'hi' } })
+      expect(response.status).toBe(500)
 
       expect(markSaturated).not.toHaveBeenCalled()
     })
diff --git a/server/apps/api/src/services/domain/openai-speech/index.ts b/server/apps/api/src/services/domain/openai-speech/index.ts
index 2b223bc18..18692b3ce 100644
--- a/server/apps/api/src/services/domain/openai-speech/index.ts
+++ b/server/apps/api/src/services/domain/openai-speech/index.ts
@@ -28,6 +28,11 @@ const SAFE_RESPONSE_HEADERS = new Set([
   'cache-control',
 ])
 
+const SAFE_ERROR_RESPONSE_HEADERS = new Set([
+  'content-type',
+  'retry-after',
+])
+
 function asRecord(value: unknown): Record<string, unknown> | undefined {
   if (typeof value !== 'object' || value == null || Array.isArray(value))
     return undefined
@@ -199,7 +204,7 @@ export function createOpenAiSpeechService(deps: OpenAiSpeechServiceDeps) {
         .warn('tts speech delivered with upstream error status')
       return new Response(response.body, {
         status: response.status,
-        headers: buildSafeResponseHeaders(response),
+        headers: buildSafeErrorResponseHeaders(response),
       })
     }
 
@@ -383,3 +388,12 @@ function buildSafeResponseHeaders(response: Response): Headers {
   })
   return headers
 }
+
+function buildSafeErrorResponseHeaders(response: Response): Headers {
+  const headers = new Headers()
+  response.headers.forEach((value, key) => {
+    if (SAFE_ERROR_RESPONSE_HEADERS.has(key.toLowerCase()))
+      headers.set(key, value)
+  })
+  return headers
+}