src/io/watchFile.test.ts flaky test on refactor branch.

```
src/io/watchFile.test.ts:
24 | watchFile(path, () => calls++, controller.signal);
25 |
26 | writeFileSync(path, '{"a":1}');
27 | writeFileSync(path, '{"a":2}');
28 | await Bun.sleep(250);
29 | expect(calls).toBe(1);
^
error: expect(received).toBe(expected)

Expected: 1
Received: 0

at (/Users/runner/work/agentcore-cli/agentcore-cli/src/io/watchFile.test.ts:29:17)

Error: Expected: 1
Received: 0

at (/Users/runner/work/agentcore-cli/agentcore-cli/src/io/watchFile.test.ts:29:17)
(fail) debounces a burst of edits into a single callback and stops on abort [257.78ms]
(pass) a missing file fails quietly rather than throwing [0.18ms]
```
Ex. https://github.com/aws/agentcore-cli/actions/runs/33117797255/job/98676836925

Seen it fail twice on MacOS, retrying fixed.

Start with the failing test in src/io/watchFile.test.ts, especially the debounced callback and abort case around line 29, and reproduce the failure on macOS if possible. Check why the two writeFileSync calls can leave calls at 0 after the 250ms wait. Done means the test reliably observes one callback for the edit burst and still verifies that abort stops watching.

Vom Indexierungsmodell aus dem Issue-Text verfasst.