fix(ai-openrouter): stop forwarding root observability metadata to the wire request (#737)

* fix(ai-openrouter): stop forwarding root observability metadata to the wire request

The OpenRouter chat-completions adapter (since 0.13.0) and responses
adapter (since 0.9.0) copied chat()'s root-level observability metadata
onto the wire as chatRequest.metadata / responsesRequest.metadata. The
@openrouter/sdk validates those fields as Record<string, string>, so
structured observability metadata (objects, arrays — the documented
usage for middleware/devtools consumers) failed client-side Zod
validation with "Input validation failed" on every call. The spread
also clobbered an intentional, correctly-typed modelOptions.metadata.

Root metadata is observability-only again (middleware, devtools, event
client) and modelOptions.metadata is the sole source for OpenRouter
wire metadata, matching every other adapter. The TextOptions.metadata
doc comment now states this contract explicitly.

Fixes #735

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

* test(ai-openrouter): drop unnecessary modelOptions cast flagged by review

modelOptions accepts { metadata } directly in the responses test, so the
OpenRouterResponsesTextProviderOptions assertion (and its out-of-order
type import, flagged by CodeRabbit) are unnecessary.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

---------

Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

Author: tombeckenham

.changeset/root-metadata-not-forwarded.md

@@ -0,0 +1,10 @@
+---
+'@tanstack/ai-openrouter': patch
+'@tanstack/ai': patch
+---
+
+fix(ai-openrouter): stop forwarding root observability `metadata` to the provider wire request (#735)
+
+The OpenRouter chat-completions adapter (since 0.13.0) and responses adapter (since 0.9.0) copied `chat()`'s root-level observability `metadata` onto the wire as `chatRequest.metadata` / `responsesRequest.metadata`. The `@openrouter/sdk` validates those fields as `Record<string, string>`, so structured observability metadata (objects, arrays — the documented usage for middleware/devtools consumers) failed client-side Zod validation with `Input validation failed` on every call. The spread also clobbered an intentional, correctly-typed `modelOptions.metadata`.
+
+Root `metadata` is observability-only again (middleware, devtools, event client) and `modelOptions.metadata` is the sole source for OpenRouter wire metadata, matching every other adapter. The `TextOptions.metadata` doc comment in `@tanstack/ai` now states this contract explicitly.

packages/ai-openrouter/src/adapters/responses-text.ts

@@ -1580,7 +1580,11 @@ export class OpenRouterResponsesTextAdapter<
     > = {
       ...modelOptions,
       model: options.model + variantSuffix,
-      ...(options.metadata !== undefined && { metadata: options.metadata }),
+      // Root `metadata` is observability-only and intentionally not forwarded:
+      // the SDK validates wire `metadata` as `Record<string, string>`, while
+      // root metadata may carry arbitrarily structured values (#735). Callers
+      // set wire metadata via `modelOptions.metadata`, which flows through
+      // the spread.
       ...(() => {
         const prompts = normalizeSystemPrompts(options.systemPrompts)
         if (prompts.length === 0) return {}

packages/ai-openrouter/src/adapters/text.ts

@@ -1156,16 +1156,15 @@ export class OpenRouterTextAdapter<
       ? convertToolsToProviderFormat(options.tools)
       : undefined
 
-    // `modelOptions` is the sole sampling surface: callers set provider-native
-    // wire names (`temperature`, `topP`, `maxCompletionTokens`, etc.) there and
-    // they flow through the spread below. The root `temperature`/`topP`/
-    // `maxTokens` fields are intentionally NOT read here. Root `metadata` is
-    // still part of the contract, so forward it the same way the responses
-    // adapter does.
+    // `modelOptions` is the sole wire surface: callers set provider-native
+    // names (`temperature`, `topP`, `maxCompletionTokens`, `metadata`, etc.)
+    // there and they flow through the spread below. Root `metadata` is
+    // observability-only (middleware, devtools, event client) and must NOT be
+    // forwarded here — it may carry arbitrarily structured values while the
+    // SDK validates `chatRequest.metadata` as `Record<string, string>` (#735).
     const request: Omit<ChatRequest, 'stream'> = {
       ...restModelOptions,
       model: options.model + variantSuffix,
-      ...(options.metadata !== undefined && { metadata: options.metadata }),
       messages,
       ...(tools && tools.length > 0 && { tools }),
     }

packages/ai-openrouter/tests/openrouter-adapter.test.ts

@@ -1533,16 +1533,39 @@ describe('OpenRouter modelOptions pass-through', () => {
     expect(params.maxCompletionTokens).toBe(9999)
   })
 
-  it('forwards root metadata to the request (same as the responses adapter)', async () => {
+  it('does not forward root observability metadata to the request (#735)', async () => {
     setupMockSdkClient(minimalStreamChunks)
     const adapter = createAdapter()
 
     for await (const _ of chat({
       adapter,
       messages: [{ role: 'user', content: 'test' }],
-      // Root `metadata` is still part of the contract; it must not be dropped
-      // by the chat-completions request builder.
-      metadata: { env: 'test' },
+      // Root `metadata` is observability-only (middleware, devtools, event
+      // client) and may carry structured values; the SDK validates wire
+      // `chatRequest.metadata` as `Record<string, string>`, so forwarding it
+      // fails client-side Zod validation on every call.
+      metadata: { tags: ['a', 'b'], prompt: { name: 'p', version: 1 } },
+    })) {
+      // consume
+    }
+
+    const [rawParams] = mockSend.mock.calls[0]!
+    const params = rawParams.chatRequest
+    expect(params).not.toHaveProperty('metadata')
+  })
+
+  it('root metadata does not clobber modelOptions.metadata (#735)', async () => {
+    setupMockSdkClient(minimalStreamChunks)
+    const adapter = createAdapter()
+
+    for await (const _ of chat({
+      adapter,
+      messages: [{ role: 'user', content: 'test' }],
+      metadata: { observationName: 'my-call' },
+      // `modelOptions.metadata` is the typed home for OpenRouter wire
+      // metadata; it must reach the request untouched even when root
+      // observability metadata is also present.
+      modelOptions: { metadata: { env: 'test' } } as OpenRouterTextModelOptions,
     })) {
       // consume
     }

packages/ai-openrouter/tests/openrouter-responses-adapter.test.ts

@@ -197,6 +197,60 @@ describe('OpenRouter responses adapter — request shape', () => {
     expect(params.model).toBe('openai/gpt-4o-mini:thinking')
   })
 
+  it('does not forward root observability metadata; modelOptions.metadata reaches the wire (#735)', async () => {
+    setupMockSdkClient([
+      {
+        type: 'response.completed',
+        sequenceNumber: 1,
+        response: {
+          model: 'openai/gpt-4o-mini',
+          output: [],
+          usage: { inputTokens: 0, outputTokens: 0, totalTokens: 0 },
+        },
+      },
+    ])
+    const adapter = createAdapter()
+    for await (const _ of chat({
+      adapter,
+      messages: [{ role: 'user', content: 'hi' }],
+      // Root `metadata` is observability-only and may carry structured
+      // values; the SDK validates wire `metadata` as `Record<string,
+      // string>`, so forwarding it fails client-side Zod validation.
+      metadata: { tags: ['a', 'b'], prompt: { name: 'p', version: 1 } },
+      // `modelOptions.metadata` is the typed home for wire metadata and
+      // must not be clobbered by root metadata.
+      modelOptions: { metadata: { env: 'test' } },
+    })) {
+      // consume
+    }
+    const params = mockSend.mock.calls[0]![0].responsesRequest
+    expect(params.metadata).toEqual({ env: 'test' })
+  })
+
+  it('omits wire metadata entirely when only root observability metadata is set (#735)', async () => {
+    setupMockSdkClient([
+      {
+        type: 'response.completed',
+        sequenceNumber: 1,
+        response: {
+          model: 'openai/gpt-4o-mini',
+          output: [],
+          usage: { inputTokens: 0, outputTokens: 0, totalTokens: 0 },
+        },
+      },
+    ])
+    const adapter = createAdapter()
+    for await (const _ of chat({
+      adapter,
+      messages: [{ role: 'user', content: 'hi' }],
+      metadata: { observationName: 'my-call' },
+    })) {
+      // consume
+    }
+    const params = mockSend.mock.calls[0]![0].responsesRequest
+    expect(params).not.toHaveProperty('metadata')
+  })
+
   it('rejects webSearchTool() as RUN_ERROR pointing at the chat adapter', async () => {
     const adapter = createAdapter()
     const ws = webSearchTool() as Tool

packages/ai/src/types.ts

@@ -820,14 +820,14 @@ export interface TextOptions<
   systemPrompts?: Array<SystemPrompt>
   agentLoopStrategy?: AgentLoopStrategy
   /**
-   * Additional metadata to attach to the request.
-   * Can be used for tracking, debugging, or passing custom information.
-   * Structure and constraints vary by provider.
+   * Observability metadata attached to this call. Surfaced to middleware,
+   * devtools, and the event client; values may be arbitrarily structured
+   * (objects, arrays). Adapters never forward this field onto the provider
+   * wire request.
    *
-   * Provider usage:
-   * - OpenAI: `metadata` (Record<string, string>) - max 16 key-value pairs, keys max 64 chars, values max 512 chars
-   * - Anthropic: `metadata` (Record<string, any>) - includes optional user_id (max 256 chars)
-   * - Gemini: Not directly available in TextProviderOptions
+   * To send provider-side request metadata, use the provider's
+   * `modelOptions` field instead, where the provider supports one (e.g.
+   * OpenAI's and OpenRouter's `metadata` are both Record<string, string>).
    */
   metadata?: Record<string, any> | undefined
   modelOptions?: TProviderOptionsForModel

testing/e2e/src/routes/api.chat.ts

@@ -90,6 +90,23 @@ export const Route = createFileRoute('/api/chat')({
               ]
             : [systemPrompt]
 
+          // Test-only flag — when set to `true`, the route passes
+          // structured root-level observability `metadata` (objects,
+          // arrays) to `chat()`. Enables root-metadata-wire.spec.ts to
+          // verify the call still completes: the adapter keeps root
+          // metadata off the provider request, so the OpenRouter SDK's
+          // Record<string, string> outbound validation never sees it
+          // (regression coverage for #735). Wire-absence itself is
+          // asserted by the adapter unit tests.
+          const rootObservabilityMetadata =
+            fp.structuredRootMetadata === true
+              ? {
+                  observationName: 'e2e-root-metadata',
+                  tags: ['a', 'b'],
+                  prompt: { name: 'p', version: 1 },
+                }
+              : undefined
+
           // Two structured-output-streaming features differ only in which
           // schema they bind to. Branched per-feature so TS can pick the
           // right `chat<TSchema>()` overload without a `never` cast.
@@ -141,6 +158,9 @@ export const Route = createFileRoute('/api/chat')({
                       messages: params.messages,
                       threadId: params.threadId,
                       runId: params.runId,
+                      ...(rootObservabilityMetadata && {
+                        metadata: rootObservabilityMetadata,
+                      }),
                       abortController,
                     })
 

testing/e2e/tests/root-metadata-wire.spec.ts

@@ -0,0 +1,68 @@
+import { test, expect } from './fixtures'
+
+/**
+ * End-to-end regression coverage for #735: root-level observability
+ * `metadata` on `chat()` must never be forwarded onto the provider wire
+ * request.
+ *
+ * In `@tanstack/ai-openrouter` 0.13.x the chat-completions mapper copied
+ * root `metadata` into OpenRouter's `chatRequest.metadata`. The
+ * `@openrouter/sdk` validates that field as `Record<string, string>`
+ * client-side, so structured observability metadata (objects, arrays —
+ * the documented usage for middleware/devtools consumers) failed Zod
+ * validation before the request ever left the process, killing every
+ * call with `RUN_ERROR`.
+ *
+ * Wire-shape coverage lives in the unit tests
+ * `packages/ai-openrouter/tests/openrouter-adapter.test.ts` and
+ * `openrouter-responses-adapter.test.ts`, which inspect the request
+ * handed to the SDK directly. What this spec covers (which those
+ * cannot): the full HTTP path — test → route → `chat()` → adapter →
+ * real `@openrouter/sdk` outbound validation — tolerates structured
+ * root metadata. Pre-fix, the SDK's own Zod schema rejects the request
+ * and the stream emits RUN_ERROR instead of completing.
+ */
+test.describe('root observability metadata — wire path', () => {
+  test('chat completes end-to-end on OpenRouter without the root metadata reaching the wire request', async ({
+    request,
+    testId,
+    aimockPort,
+  }) => {
+    const body = {
+      threadId: 'thread-root-meta-1',
+      runId: 'run-root-meta-1',
+      state: {},
+      messages: [
+        { id: 'u1', role: 'user', content: '[chat] recommend a guitar' },
+      ],
+      tools: [],
+      context: [],
+      forwardedProps: {
+        provider: 'openrouter',
+        feature: 'chat',
+        testId,
+        aimockPort,
+        // Opt-in flag handled by `api.chat.ts` — passes structured
+        // root-level observability metadata (arrays, nested objects) to
+        // `chat()`. The adapter must keep it off the provider request;
+        // pre-fix, the SDK's own outbound Zod validation rejects the
+        // request before it reaches aimock and the stream ends in
+        // RUN_ERROR.
+        structuredRootMetadata: true,
+      },
+    }
+    const response = await request.post('/api/chat', {
+      data: body,
+      headers: { 'Content-Type': 'application/json' },
+    })
+    expect(
+      response.ok(),
+      `expected 200, got ${response.status()}: ${await response.text()}`,
+    ).toBe(true)
+    const text = await response.text()
+    expect(text).toContain('RUN_FINISHED')
+    // No RUN_ERROR — the @openrouter/sdk's outbound Record<string, string>
+    // validation never saw the structured metadata.
+    expect(text).not.toContain('RUN_ERROR')
+  })
+})