[P4] Corpus: PLATFORM_THREAD_PER_TASK's executor probe has no pair #1182

#1185 pairs the detector's churn branch, which reads no clock. Its other branch, registerExecutor probing a thread-per-task executor against a 200 ms deadline, is held only by its unit test.

Why not now. A firing row would depend on a task starting within 200 ms, which is a flaky gate on a loaded runner. The twin, a virtual executor, is structural.

What it would take. Several executors per run, so that any probe answering fires, and a measured failure rate over CI runs before trusting it.