test: verify native timeout reaping from parent child identity

[roodboi]

The native-runtime-client timeout test could fail under load after correctly killing its child: its 250 ms deadline begins at spawn, but its reaping assertions depended on marker files written later by the child.

Observe the real spawn result for the exact fixture binary and require one child, settled exit completion, SIGKILL, and ESRCH for that parent-captured PID. The deadline case now deliberately waits before writing either marker. Pre-aborted requests still require zero spawns, and running cancellation still requires the exact marker and matching child PID. The pass-through spy is restored in finally; production code and timeout budgets are unchanged.

Validation: focused runtime-client tests (12 passed); full CLI suite (1,835 passed, 67 skipped, zero failures); CLI/root typecheck; root check; changed-file lint; and staged privacy checks passed with pinned Bun 1.4.2. The CLI tasks ran fresh; unchanged DB tasks used the shared cache. These checks do not qualify native VM behavior.

Release signal: test-only verification correction. This does not fix or qualify the separate native HTTPS release failure.

---

^{Need help on this PR? Tag @codesmith-bot with what you need. Autofix is disabled.}