tip-leaf: refresh effect flock heartbeat timestamps (origin #51248)

[kvnloo]

Origin

anomalyco#51248

Intent

Wrap heartbeat utimes in Effect.suspend so each spaced repeat evaluates a fresh Date instead of stamping the lock with a once-captured time.

Paths

• packages/core/src/util/effect-flock.ts
• packages/core/test/util/effect-flock.test.ts

Base

dev @ 696f41bc8e (synced from upstream/dev; prior tip was adee738)

Notes

github_writes_origin=0. Codex promote parked.