feat(S-103): Test-drive and implement --debug diagnostic mode

tools/ai-cli-dispatch/tests/cli.test.ts

@@ -406,4 +406,91 @@ describe("main", () => {
       out.restore();
     }
   });
+
+  it("run prints debug diagnostic JSON to stderr with --debug", async () => {
+    const out = captureOutput();
+    const stderrChunks: string[] = [];
+    try {
+      const code = await main(
+        ["node", "cli.ts", "run", "--client", "codex", "--prompt", "hello", "--debug"],
+        {
+          detectClients: () => mockClients,
+          executePrompt: async (_client, _prompt, options?) => {
+            options?.onDebug?.({
+              command: "codex",
+              args: ["exec", "--yolo", "hello"],
+              pid: 12345,
+              exitCode: 0,
+              exitSignal: null,
+              durationMs: 42,
+              stderrLength: 0,
+              stdoutLength: 6,
+            } as any);
+            return {
+              stdout: "output",
+              stderr: "",
+              exitCode: 0,
+              client: "codex",
+              durationMs: 42,
+            };
+          },
+          stderrWrite: (chunk) => stderrChunks.push(chunk),
+        }
+      );
+      assert.strictEqual(code, 0);
+      assert.strictEqual(stderrChunks.length, 1);
+      const diag = JSON.parse(stderrChunks[0]);
+      assert.strictEqual(diag.command, "codex");
+      assert.deepStrictEqual(diag.args, ["exec", "--yolo", "hello"]);
+      assert.strictEqual(diag.pid, 12345);
+      assert.strictEqual(diag.exitCode, 0);
+      assert.strictEqual(diag.exitSignal, null);
+      assert.strictEqual(diag.durationMs, 42);
+      assert.strictEqual(diag.stderrLength, 0);
+    } finally {
+      out.restore();
+    }
+  });
+
+  it("dispatch prints debug diagnostic JSON to stderr with --debug", async () => {
+    const out = captureOutput();
+    const stderrChunks: string[] = [];
+    try {
+      const code = await main(
+        ["node", "cli.ts", "dispatch", "do something", "--debug"],
+        {
+          detectClients: () => mockClients,
+          executePrompt: async (_client, _prompt, options?) => {
+            options?.onDebug?.({
+              command: "codex",
+              args: ["exec", "--yolo", "do something"],
+              pid: 12345,
+              exitCode: 0,
+              exitSignal: null,
+              durationMs: 42,
+              stderrLength: 0,
+              stdoutLength: 6,
+            } as any);
+            return {
+              stdout: "output",
+              stderr: "",
+              exitCode: 0,
+              client: "codex",
+              durationMs: 42,
+            };
+          },
+          resolveClient: () => "codex",
+          resolveConfig: () => ({ paths: {}, timeout: 600_000 }),
+          stderrWrite: (chunk) => stderrChunks.push(chunk),
+        }
+      );
+      assert.strictEqual(code, 0);
+      assert.strictEqual(stderrChunks.length, 1);
+      const diag = JSON.parse(stderrChunks[0]);
+      assert.strictEqual(diag.command, "codex");
+      assert.strictEqual(diag.durationMs, 42);
+    } finally {
+      out.restore();
+    }
+  });
 });

tools/ai-cli-dispatch/tests/execute.test.ts

@@ -16,6 +16,7 @@ interface MockScenario {
 
 function createMockChildProcess(scenario: MockScenario): any {
   const child = new EventEmitter() as any;
+  child.pid = 12345;
   child.stdout = Readable.from(
     scenario.stdout !== undefined ? [scenario.stdout] : []
   );
@@ -257,4 +258,66 @@ describe("executePrompt", () => {
       global.setTimeout = origSetTimeout;
     }
   });
+
+  it("emits debug info via onDebug when debug is true for successful execution", async () => {
+    const scenarios = new Map<string, MockScenario>([
+      ["codex exec --yolo hello", { stdout: "ok", stderr: "warn", exitCode: 0 }],
+    ]);
+    const debugInfos: any[] = [];
+    const result = await executePrompt("codex", "hello", {
+      spawn: mockSpawn(scenarios),
+      existsSync: () => true,
+      debug: true,
+      onDebug: (info) => debugInfos.push(info),
+    });
+    assert.strictEqual(result.exitCode, 0);
+    assert.strictEqual(debugInfos.length, 1);
+    const info = debugInfos[0];
+    assert.strictEqual(info.command, "codex");
+    assert.deepStrictEqual(info.args, ["exec", "--yolo", "hello"]);
+    assert.strictEqual(info.pid, 12345);
+    assert.strictEqual(info.exitCode, 0);
+    assert.strictEqual(info.exitSignal, null);
+    assert.strictEqual(info.stderrLength, 4);
+    assert.strictEqual(info.stdoutLength, 2);
+    assert.strictEqual(typeof info.durationMs, "number");
+    assert.ok(info.durationMs >= 0);
+  });
+
+  it("emits debug info via onDebug when debug is true for failed execution", async () => {
+    const scenarios = new Map<string, MockScenario>([
+      ["codex exec --yolo fail", { stdout: "", stderr: "error", exitCode: 1 }],
+    ]);
+    const debugInfos: any[] = [];
+    const result = await executePrompt("codex", "fail", {
+      spawn: mockSpawn(scenarios),
+      existsSync: () => true,
+      debug: true,
+      onDebug: (info) => debugInfos.push(info),
+    });
+    assert.strictEqual(result.exitCode, 1);
+    assert.strictEqual(debugInfos.length, 1);
+    assert.strictEqual(debugInfos[0].exitCode, 1);
+    assert.strictEqual(debugInfos[0].stderrLength, 5);
+    assert.strictEqual(debugInfos[0].stdoutLength, 0);
+  });
+
+  it("emits debug info via onDebug for spawn errors", async () => {
+    const scenarios = new Map<string, MockScenario>();
+    const debugInfos: any[] = [];
+    await assert.rejects(
+      executePrompt("codex", "hello", {
+        spawn: mockSpawn(scenarios),
+        existsSync: () => true,
+        debug: true,
+        onDebug: (info) => debugInfos.push(info),
+      }),
+      (err: unknown) => err instanceof ClientNotFoundError
+    );
+    assert.strictEqual(debugInfos.length, 1);
+    assert.strictEqual(debugInfos[0].command, "codex");
+    assert.deepStrictEqual(debugInfos[0].args, ["exec", "--yolo", "hello"]);
+    assert.strictEqual(debugInfos[0].exitCode, null);
+    assert.strictEqual(debugInfos[0].exitSignal, null);
+  });
 });