fix(tooling): surface non-executable tool-use warnings

src/models/openai.oauth.test.ts

@@ -69,4 +69,40 @@ describe('OpenAIClient OAuth (Codex)', () => {
     expect(resp.content).toBe('hello');
     expect(resp.usage).toEqual({ inputTokens: 2, outputTokens: 2 });
   });
+
+  it('adds provider warning when tools are requested in OAuth mode', async () => {
+    const sse = makeSse([
+      { event: 'response.output_text.delta', data: { type: 'response.output_text.delta', delta: 'result body' } },
+      { event: 'response.completed', data: { type: 'response.completed', response: { usage: { input_tokens: 1, output_tokens: 1 } } } },
+    ]);
+
+    globalThis.fetch = vi.fn(async () => {
+      const stream = new ReadableStream({
+        start(controller) {
+          controller.enqueue(new TextEncoder().encode(sse));
+          controller.close();
+        },
+      });
+      return new Response(stream, { status: 200 });
+    }) as typeof fetch;
+
+    const client = new OpenAIClient({ model: 'gpt-5.3-codex', useOAuth: true });
+    const resp = await client.chat({
+      system: 'You are helpful.',
+      messages: [{ role: 'user', content: 'use tools' }],
+      tools: [{
+        name: 'gmail_read',
+        description: 'Read Gmail message',
+        input_schema: {
+          type: 'object',
+          properties: { id: { type: 'string' } },
+          required: ['id'],
+        },
+      }],
+    });
+
+    expect(resp.content).toContain('[provider-warning] OpenAI OAuth (Codex backend) does not support tool execution in Flynn yet.');
+    expect(resp.content).toContain('Requested tools were not sent to the provider');
+    expect(resp.content).toContain('result body');
+  });
 });

src/models/openai.ts

@@ -213,8 +213,18 @@ export class OpenAIClient implements ModelClient {
       }
     }
 
+    const toolsRequested = Boolean(request.tools && request.tools.length > 0);
+    const content = toolsRequested
+      ? [
+        '[provider-warning] OpenAI OAuth (Codex backend) does not support tool execution in Flynn yet.',
+        'Requested tools were not sent to the provider, so any textual tool_use output is not executable.',
+        '',
+        outputText,
+      ].join('\n')
+      : outputText;
+
     return {
-      content: outputText,
+      content,
       stopReason: 'end_turn',
       usage: usage ?? { inputTokens: 0, outputTokens: 0 },
     };