test: trigger preview retirement after the initial result

[huangruiteng]

The retirement recovery test shortens the five-minute worker lifetime to 200ms from spawn. On a slow worker, that can retire the first accepted request before its result, so the test never reaches the intended second-request cleanup race. A synthetic 350ms worker startup delay reproduces the lifetime failure on the current main baseline 99839aeb8fed5fae38a5d319391cd050672a6508 (idle and broken-pipe variants pass).

Advance the selected retirement timers through a test-only SIGUSR2 preload after the first preview has completed. The real Host cleanup grace, request deadline, process-group ownership and retirement fence remain in use. Add ready/350ms worker variants for idle, lifetime and broken-pipe retirement. Cleared timer handles are excluded; the replacement supervisor retains its original production clocks. No production code or timeout changes.

Validation on macOS / Node 24.21.0 / Python 3.12.15:

• Full tests/test_delegation_preview_reuse.py: 41 passed.
• All six retirement variants under two pytest workers with an additional 350ms startup delay: 6 passed.
• Native delegation_preview_bridge, host_process_group and host_process TypeScript tests: 24 passed.
• Python compile and git diff --check: passed.

Linux qualification remains required. This fixes a demonstrated test timing defect; it does not establish that every Linux CI failure has the same cause. The separate test_retry_safe_typed_write_recovers_after_unexpected_runtime_exit failure remains unexplained: 25 consecutive current-main macOS trials pass, which is not a Linux waiver. Existing accepted-request failure/uncertain-cleanup tests are retained. No model, live connector or production installation was changed.

Linux CI checkpoint on exact head b201ba28941b7af3b57bf8fb33bfd5080be4720c: all six new ready/slow-worker retirement variants are passed in the four uploaded Python JUnit shard artifacts from run 37171421012. The separate unexpected-exit typed-write recovery case also passed in that run. Overall CI remains failed (72 failing test names); the preview suite has 40 passed and one existing backpressure/deadline failure. These artifacts qualify the six cases, without attributing or waiving other failures or the earlier unexplained runtime exit.