fix(adapters): support structured output for Google and CCA models

src/adapters/google-wire-compiler.ts

@@ -141,6 +141,16 @@ function compileGenerationConfig(value: unknown): JsonObject | undefined {
     const valid = value.responseModalities.filter((m): m is string => typeof m === "string" && ["TEXT", "IMAGE", "AUDIO"].includes(m));
     if (valid.length > 0) out.responseModalities = valid;
   }
+  // Structured output. This compiler is an allowlist, so without these two the adapter
+  // could set a schema and it would still be dropped before the wire.
+  if (typeof value.responseMimeType === "string" && value.responseMimeType.length > 0) {
+    out.responseMimeType = value.responseMimeType;
+  }
+  // Carried through unmodified: a caller-authored output schema is not a tool
+  // declaration, so sanitizeGeminiToolParameters must not touch it.
+  if (isObject(value.responseJsonSchema)) {
+    out.responseJsonSchema = value.responseJsonSchema;
+  }
   return Object.keys(out).length > 0 ? out : undefined;
 }
 

src/adapters/google.ts

@@ -786,6 +786,18 @@ export function createGoogleAdapter(provider: OcxProviderConfig): ProviderAdapte
       : {}),
 
     async buildRequest(parsed: OcxParsedRequest) {
+      const requestedTextFormat = parsed.options.textFormat;
+      if (requestedTextFormat) {
+        if (isImageCapableModel(parsed.modelId)) {
+          throw new Error(
+            "google image-capable models cannot combine image output with structured output — "
+            + "remove response_format or select a text model",
+          );
+        }
+        if (requestedTextFormat.type === "json_schema" && !requestedTextFormat.schema) {
+          throw new Error("google structured output requires text.format.schema for type json_schema");
+        }
+      }
       const routedModelId = provider.googleMode === "cloud-code-assist"
         ? resolveAntigravityEffortWireModel(
             parsed.modelId,
@@ -841,6 +853,13 @@ export function createGoogleAdapter(provider: OcxProviderConfig): ProviderAdapte
       if (!generationConfig.thinkingConfig && isImageCapableModel(parsed.modelId)) {
         generationConfig.responseModalities = ["TEXT", "IMAGE"];
       }
+      const textFormat = parsed.options.textFormat;
+      if (textFormat) {
+        generationConfig.responseMimeType = "application/json";
+        if (textFormat.type === "json_schema" && textFormat.schema) {
+          generationConfig.responseJsonSchema = textFormat.schema;
+        }
+      }
       if (Object.keys(generationConfig).length > 0) body.generationConfig = generationConfig;
 
       const method = parsed.stream ? "streamGenerateContent" : "generateContent";

tests/adapters/google/google-adapter.test.ts

@@ -583,3 +583,100 @@ describe("google adapter — direct -tiered wire renames", () => {
     }
   });
 });
+
+describe("google adapter — structured output", () => {
+  test("carries json_schema format into generationConfig responseMimeType and responseJsonSchema", async () => {
+    const parsed = {
+      modelId: "gemini-2.5-flash",
+      stream: false,
+      options: {
+        textFormat: {
+          type: "json_schema",
+          name: "output_schema",
+          schema: {
+            type: "object",
+            properties: { answer: { type: "string" } },
+            required: ["answer"],
+          },
+        },
+      },
+      context: { messages: [{ role: "user", content: "hello" }] },
+    } as unknown as OcxParsedRequest;
+
+    const body = await geminiBody(parsed);
+    const gc = body.generationConfig as Record<string, unknown>;
+    expect(gc.responseMimeType).toBe("application/json");
+    expect(gc.responseJsonSchema).toEqual({
+      type: "object",
+      properties: { answer: { type: "string" } },
+      required: ["answer"],
+    });
+  });
+
+  test("carries structured output through Cloud Code Assist envelope", async () => {
+    const ccaProvider = {
+      adapter: "google",
+      baseUrl: "https://daily-cloudcode-pa.googleapis.com",
+      googleMode: "cloud-code-assist" as const,
+      apiKey: "test-token",
+      project: "test-project",
+    };
+    const parsed = {
+      modelId: "gemini-3.8-flash",
+      stream: false,
+      options: {
+        textFormat: {
+          type: "json_schema",
+          name: "decision_format",
+          schema: {
+            type: "object",
+            properties: { decision: { type: "string" } },
+            required: ["decision"],
+          },
+        },
+      },
+      context: { messages: [{ role: "user", content: "review request" }] },
+    } as unknown as OcxParsedRequest;
+
+    const request = await createGoogleAdapter(ccaProvider).buildRequest(parsed);
+    const envelope = JSON.parse(request.body) as Record<string, unknown>;
+    const req = envelope.request as Record<string, unknown>;
+    const gc = req.generationConfig as Record<string, unknown>;
+    expect(gc.responseMimeType).toBe("application/json");
+    expect(gc.responseJsonSchema).toEqual({
+      type: "object",
+      properties: { decision: { type: "string" } },
+      required: ["decision"],
+    });
+  });
+
+  test("refuses structured output for image capable models", async () => {
+    const parsed = {
+      modelId: "gemini-3.1-flash-image",
+      stream: false,
+      options: {
+        textFormat: { type: "json_object" },
+      },
+      context: { messages: [{ role: "user", content: "generate image" }] },
+    } as unknown as OcxParsedRequest;
+
+    expect(createGoogleAdapter(provider).buildRequest(parsed)).rejects.toThrow(
+      "google image-capable models cannot combine image output with structured output",
+    );
+  });
+
+  test("refuses json_schema without schema", async () => {
+    const parsed = {
+      modelId: "gemini-2.5-flash",
+      stream: false,
+      options: {
+        textFormat: { type: "json_schema" },
+      },
+      context: { messages: [{ role: "user", content: "hello" }] },
+    } as unknown as OcxParsedRequest;
+
+    expect(createGoogleAdapter(provider).buildRequest(parsed)).rejects.toThrow(
+      "google structured output requires text.format.schema for type json_schema",
+    );
+  });
+});