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__/agent-session-helpers.test.ts

@@ -0,0 +1,24 @@
+import { describe, expect, it } from "vitest";
+import { extractRuntimeHint } from "../agent-session-helpers.js";
+
+describe("extractRuntimeHint", () => {
+  it("returns undefined for undefined config", () => {
+    expect(extractRuntimeHint(undefined)).toBeUndefined();
+  });
+
+  it("returns undefined when runtimeHint key is missing", () => {
+    expect(extractRuntimeHint({})).toBeUndefined();
+  });
+
+  it("returns normalized runtime hint when configured", () => {
+    expect(extractRuntimeHint({ runtimeHint: " openclaw " })).toBe("openclaw");
+  });
+
+  it("returns undefined for whitespace-only runtimeHint", () => {
+    expect(extractRuntimeHint({ runtimeHint: "   " })).toBeUndefined();
+  });
+
+  it("returns undefined for non-string runtimeHint", () => {
+    expect(extractRuntimeHint({ runtimeHint: 42 })).toBeUndefined();
+  });
+});