test(orchestrator): verify agent is preserved across fallback replay

Add two cases to the orchestrator test suite:
- agent name from the failing message is passed to session.prompt
- agent is omitted (undefined) when it could not be resolved

Also extend MockClientCalls.prompt to capture the agent field.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: blazejpawlak

test/helpers/mock-client.ts

@@ -11,7 +11,7 @@ export interface MockMessageEntry {
 export interface MockClientCalls {
   abort: string[];
   revert: Array<{ sessionId: string; messageID: string }>;
-  prompt: Array<{ sessionId: string; providerID: string; modelID: string; parts: unknown[] }>;
+  prompt: Array<{ sessionId: string; providerID: string; modelID: string; agent?: string; parts: unknown[] }>;
   toasts: Array<{ title?: string; message: string; variant: string }>;
   logs: Array<{ level: string; message: string }>;
 }
@@ -52,13 +52,14 @@ export function makeMockClient(opts: MockClientOptions = {}): {
       },
       prompt: async (options: {
         path: { id: string };
-        body?: { model?: { providerID: string; modelID: string }; parts?: unknown[] };
+        body?: { model?: { providerID: string; modelID: string }; agent?: string; parts?: unknown[] };
       }) => {
         if (opts.promptError) throw opts.promptError;
         calls.prompt.push({
           sessionId: options.path.id,
           providerID: options.body?.model?.providerID ?? "",
           modelID: options.body?.model?.modelID ?? "",
+          agent: options.body?.agent,
           parts: options.body?.parts ?? [],
         });
         return { data: {} };

test/orchestrator.test.ts

@@ -453,6 +453,41 @@ describe("attemptFallback — concurrency", () => {
   });
 });
 
+// ─── Agent preservation ───────────────────────────────────────────────────────
+
+describe("attemptFallback — agent preservation", () => {
+  it("passes the agent name to the prompt call so the fallback model runs under the same agent", async () => {
+    const { client, calls } = makeMockClient({
+      messages: [makeUserMessage("s1", "m1", "openai", "gpt-5.3-codex", "OpenCoder")],
+    });
+    const store = makeStore();
+    store.sessions.setOriginalModel("s1", "openai/gpt-5.3-codex");
+    const logger = new Logger(client, "/tmp/test.log", false);
+
+    await attemptFallback("s1", "rate_limit", client, store, BASE_CONFIG, logger, "/tmp");
+
+    expect(calls.prompt).toHaveLength(1);
+    expect(calls.prompt[0].agent).toBe("OpenCoder");
+  });
+
+  it("omits agent from prompt when it could not be resolved", async () => {
+    // No agent field in the message → agentName resolves to null
+    const msg = makeUserMessage("s1", "m1", "openai", "gpt-5.3-codex");
+    // Strip the agent field so resolveAgentName has nothing to work with
+    (msg.info as any).agent = undefined;
+
+    const { client, calls } = makeMockClient({ messages: [msg] });
+    const store = makeStore();
+    store.sessions.setOriginalModel("s1", "openai/gpt-5.3-codex");
+    const logger = new Logger(client, "/tmp/test.log", false);
+
+    await attemptFallback("s1", "rate_limit", client, store, BASE_CONFIG, logger, "/tmp");
+
+    expect(calls.prompt).toHaveLength(1);
+    expect(calls.prompt[0].agent).toBeUndefined();
+  });
+});
+
 // ─── Replay step failures ─────────────────────────────────────────────────────
 
 describe("attemptFallback — replay step failures", () => {