feat(FN-2617): merge fusion/fn-2617 (auto-resolved)

- test(FN-2617): stabilize workflow remediation timeout under full suite
- test(FN-2617): complete Step 5 — add openclaw runtime resolution coverage
- feat(FN-2617): complete Step 4 — route step sessions through runtime resolution
- fix(FN-2617): thread runtimeHint through merger rebase push flow
- feat(FN-2617): complete Step 3 — wire runtimeHint across engine subsystems
- feat(FN-2617): complete Step 2 — thread runtimeHint in executor paths
- feat(FN-2617): complete Step 1 — add runtimeHint extraction helper

packages/engine/src/__tests__/step-session-executor.test.ts

@@ -546,6 +546,25 @@ vi.mock("../pi.js", () => ({
   compactSessionContext: vi.fn(),
 }));
 
+vi.mock("../agent-session-helpers.js", async () => {
+  const pi = await import("../pi.js");
+  return {
+    createResolvedAgentSession: vi.fn(async (options: any) => {
+      const result = await pi.createFnAgent(options);
+      return {
+        session: result.session,
+        sessionFile: result.sessionFile,
+        runtimeId: "pi",
+        wasConfigured: false,
+      };
+    }),
+    promptWithAutoRetry: vi.fn(async (session: any, prompt: string, options?: unknown) =>
+      pi.promptWithFallback(session, prompt, options as any),
+    ),
+    describeAgentModel: vi.fn(async (session: any) => pi.describeModel(session)),
+  };
+});
+
 // Mock logger
 vi.mock("../logger.js", () => {
   const createMockLogger = () => ({