test(runtime): make cleanup deadlines deterministic

[drewstone]

Problem

The exact 0.119.1 release run exposed two checks tied to host scheduling speed: a 20 ms cleanup cancellation was required to finish within 250 ms of wall time, and a real Git/worktree activation flow had only 15 seconds for its full process boundary.

Change

Drive the cleanup deadline with the fake clock and directly assert that the stop signal was aborted. Give the three Git-heavy activation checks a 60-second outer timeout without changing their behavior assertions.

Evidence

• Focused: 2 files passed, 31/31 tests, 25.06 s.
• Full: 197 files passed, 2 skipped; 2,261 passed, 6 skipped, 44.66 s.
• git diff --check: clean.
• git merge-tree --write-tree origin/main HEAD: 59677f694e60bbe41bb606b11891099ea42fb7b3.

[tangletools]

✅ Auto-approved drewstone PR — 9c6ee1f8

This PR was opened by the trusted drewstone account.
The full PR reviewer audit still runs separately and will publish findings if it detects issues.

_{tangletools · auto-approval · reason: drewstone_author · 2026-08-01T23:08:26Z}