test: allow lifecycle helper startup on CI

[webup]

Summary

• make the POSIX timeout-fallback regression model a deliberately slow helper startup
• allow five seconds for AgentSeek to start that helper before exercising fallback cleanup
• retain tight bounded cleanup assertions after the timeout

Why

The AgentSeek 0.1.3 post-merge macOS run started the real helper more slowly than the former two-second test window, so the test timed out before its marker existed. The release implementation itself was not the failure. This change reproduces that race deterministically with a 2.5-second helper delay and verifies the cleanup contract after readiness.

Verification

• RED: slow-start regression failed with the former two-second window because the marker was absent
• GREEN: focused regression passed in 5.49s
• full suite: 1217 passed, 1 skipped
• all pre-commit hooks passed
• ty passed
• git diff --check passed

Scope

Exactly one test file; no package, lock, release-coordinate, workflow, or production code changes.