fix(google): allow structured output for Gemini models on Cloud Code Assist

src/adapters/google.ts

@@ -796,14 +796,14 @@ export function createGoogleAdapter(provider: OcxProviderConfig): ProviderAdapte
       // body, URL or credential.
       const requestedTextFormat = parsed.options.textFormat;
       if (requestedTextFormat) {
-        if (provider.googleMode === "cloud-code-assist") {
-          // Not implemented or verified by opencodex for the Cloud Code Assist envelope,
-          // including Claude models served through it. This is not a claim that the
-          // upstream cannot do it — silence would return unconstrained prose as success,
-          // which is the failure this fix exists to remove.
+        if (provider.googleMode === "cloud-code-assist" && !parsed.modelId.startsWith("gemini-")) {
+          // Not implemented by opencodex for non-Gemini models (including Claude)
+          // served through the Cloud Code Assist envelope. This is not a claim that
+          // the upstream cannot do it — silence would return unconstrained prose as success,
+          // which is the failure this refusal exists to prevent.
           throw new Error(
-            "google cloud-code-assist structured output is not implemented by opencodex — "
-            + "remove response_format or route this model through AI Studio or Vertex",
+            "google cloud-code-assist structured output is not implemented by opencodex for non-Gemini models — "
+            + "remove response_format or route this model through a direct provider",
           );
         }
         if (isImageCapableModel(parsed.modelId)) {

structure/providers/google.md

@@ -62,12 +62,13 @@ The schema is carried verbatim. `sanitizeGeminiToolParameters` narrows a schema
 the function-declaration subset and must never be applied to a caller-authored output
 schema. `compileGenerationConfig` in `google-wire-compiler.ts` is a whitelist, so
 both keys are listed there as well; setting them in the adapter alone would drop them
-before the wire.
+before the wire. On Cloud Code Assist, Gemini models carry these same keys inside
+`envelope.request.generationConfig`.
 
 Three cases refuse explicitly rather than dropping the constraint silently:
-cloud-code-assist, which opencodex does not implement or verify for this field
-(including Claude models served through that envelope — this is not a claim about
-what the upstream can do); an image-capable model, whose `responseModalities`
+non-Gemini models on Cloud Code Assist (such as Claude models served through that
+envelope), which opencodex does not implement or verify for this field (this is not
+a claim about what the upstream can do); an image-capable model, whose `responseModalities`
 configuration contradicts JSON-constrained text; and a `json_schema` format carrying
 no schema, which would otherwise downgrade to bare JSON mode. An image-capable model
 with no structured-output request keeps its existing `responseModalities` behavior.

tests/adapters/google/google-structured-output.test.ts

@@ -17,7 +17,17 @@ import type { OcxParsedRequest, OcxProviderConfig } from "../../../src/types";
 
 const aiStudio = { adapter: "google", baseUrl: "https://generativelanguage.googleapis.com", apiKey: "key" } as unknown as OcxProviderConfig;
 const vertex = { adapter: "google", googleMode: "vertex", baseUrl: "https://aiplatform.googleapis.com", apiKey: "key" } as unknown as OcxProviderConfig;
-const cca = { adapter: "google", googleMode: "cloud-code-assist", baseUrl: "https://cloudcode-pa.googleapis.com", apiKey: "token" } as unknown as OcxProviderConfig;
+const cca = { adapter: "google", googleMode: "cloud-code-assist", baseUrl: "https://cloudcode-pa.googleapis.com", apiKey: "token", project: "test-project" } as unknown as OcxProviderConfig;
+type CloudCodeAssistEnvelope = {
+  generationConfig?: unknown;
+  request?: {
+    generationConfig?: {
+      responseMimeType?: unknown;
+      responseJsonSchema?: unknown;
+      responseSchema?: unknown;
+    };
+  };
+};
 
 const SCHEMA = {
   type: "object",
@@ -57,6 +67,27 @@ describe("F3 Google structured output reaches the generateContent wire", () => {
     expect(config.responseJsonSchema).toEqual(SCHEMA);
   });
 
+  test("Gemini-on-CCA carries responseMimeType and responseJsonSchema inside envelope.request", async () => {
+    const { body } = await createGoogleAdapter(cca).buildRequest(
+      parsed({ type: "json_schema", name: "answer", schema: SCHEMA, strict: true }),
+    );
+    const envelope = JSON.parse(typeof body === "string" ? body : JSON.stringify(body)) as CloudCodeAssistEnvelope;
+
+    expect(envelope.generationConfig).toBeUndefined();
+    expect(envelope.request?.generationConfig?.responseMimeType).toBe("application/json");
+    expect(envelope.request?.generationConfig?.responseJsonSchema).toEqual(SCHEMA);
+    expect(envelope.request?.generationConfig?.responseSchema).toBeUndefined();
+  });
+
+  test("json_object on Cloud Code Assist sets only responseMimeType in envelope.request", async () => {
+    const { body } = await createGoogleAdapter(cca).buildRequest(parsed({ type: "json_object" }));
+    const envelope = JSON.parse(typeof body === "string" ? body : JSON.stringify(body)) as CloudCodeAssistEnvelope;
+
+    expect(envelope.generationConfig).toBeUndefined();
+    expect(envelope.request?.generationConfig?.responseMimeType).toBe("application/json");
+    expect(envelope.request?.generationConfig?.responseJsonSchema).toBeUndefined();
+  });
+
   test("the schema survives compilation byte-for-byte, unsanitized", async () => {
     const nested = {
       type: "object",
@@ -86,8 +117,10 @@ describe("F3 Google structured output reaches the generateContent wire", () => {
 });
 
 describe("F3 unsupported modes refuse explicitly instead of dropping the schema", () => {
-  test("cloud-code-assist reports that opencodex does not implement it", async () => {
-    const promise = createGoogleAdapter(cca).buildRequest(parsed({ type: "json_schema", schema: SCHEMA }));
+  test("Claude-on-CCA with textFormat reports that opencodex does not implement it", async () => {
+    const promise = createGoogleAdapter(cca).buildRequest(
+      parsed({ type: "json_schema", schema: SCHEMA }, "claude-3-7-sonnet"),
+    );
     await expect(promise).rejects.toThrow(/not implemented by opencodex/);
   });
 
@@ -98,6 +131,13 @@ describe("F3 unsupported modes refuse explicitly instead of dropping the schema"
     await expect(promise).rejects.toThrow(/cannot combine image output with structured output/);
   });
 
+  test("an image-capable Cloud Code Assist model refuses the structured-output conflict", async () => {
+    const promise = createGoogleAdapter(cca).buildRequest(
+      parsed({ type: "json_schema", schema: SCHEMA }, "gemini-3-pro-image-preview"),
+    );
+    await expect(promise).rejects.toThrow("cannot combine image output with structured output");
+  });
+
   test("an image-capable model with NO schema keeps its image behavior", async () => {
     const config = await generationConfig(aiStudio, parsed(undefined, "gemini-3-pro-image-preview"));