Flaky test: "a mandatory call deadline overrides requestTimeoutMs: 0" races a fixed sleep against a child's 300 ms reply #478

What's wrong

test/mcpl-request-timeout.test.ts:164-189 (main e670363) is flaky. The test:

1. spawns a stub server whose tools/call answers 300 ms after it receives the call;
2. calls with a 75 ms deadline;
3. sleeps a fixed 350 ms after the rejection;
4. asserts that exactly one orphaned-response arrived.

That leaves about 125 ms of slack. On a loaded runner the reply lands after the sleep, so the test sees [] and fails.

Why it matters

It turns main red with no code change. CI for cabf3d0 (the merge of #412, Oct 18) failed only on macOS / Node 24, only in this test (actual: []). The next merge passed. #407 fixed the same class of problem in the guard's #281 tests.

How it was found

While checking whether main's red CI matched the red check on #372 (Actions run 39087371623).

Suggested fix

Wait for the event rather than sleeping: once(connection, 'orphaned-response'), raced against a timeout of several seconds.

Found during our review of #372: #372 (review)

_{Posted by the maintainer's desk assistant.}