[deanq]

Summary

When the Flash build artifact was not on the volume at container start, maybe_unpack() slept a fixed 30s (DEFAULT_TARBALL_UNPACK_INTERVAL) before retrying, even if the artifact landed a moment later.

• Retry every 0.5s until a 60s deadline. The worst case is unchanged: 3 attempts with 30s between them was 60s.
• Extraction errors are retried too, since a partially written tarball fails to extract.
• Logging: one warning when the wait starts, one info line with the wait time on recovery, and one error at the deadline. Before, every attempt logged an error with a traceback; logging every poll would mean up to 120 lines.
• DEFAULT_TARBALL_UNPACK_ATTEMPTS and DEFAULT_TARBALL_UNPACK_INTERVAL are replaced by DEFAULT_TARBALL_UNPACK_TIMEOUT and DEFAULT_TARBALL_UNPACK_POLL_INTERVAL. Nothing else referenced the old names.

Impact

Measured cold start on an RTX 4090 (SLS-811), with container start at t=0:

Event	t
first attempt: flash build artifact not found	1.3s
second attempt succeeds	33.4s
result posted	38.5s

About 32s of the ~38s in-container start was this sleep. With this change, a late artifact is picked up within 0.5s of landing.

Test plan

• New: an artifact missing on the first attempt and present on the second is unpacked after ≤1s of waiting (fails on main: waits 30s)
• New: a missing artifact is retried until the 60s deadline, then raises with the last error chained
• Existing failure tests moved to a fake clock; the logging test asserts one warning and one error
• make quality-check: 295 passed, 78.49% coverage, 14/14 local handler tests
• Confirm on a real worker after the image is published: the log shows artifact unpacked after Xs of retries instead of a 30s gap

Linear: SLS-812 (related: SLS-811)

[Copilot]

🟢 Approval recommended

The focused retry change and updated tests have no identified blocking issues.

No open issues 🎉

What changed in this PR

Reduces worker startup delays when build artifacts arrive late on the mounted volume.

Changes:

• Replaces fixed retries with 0.5-second polling under a 60-second deadline.
• Consolidates retry logging.
• Adds fake-clock tests for timeout handling and prompt recovery.

File	Description
tests/​unit/​test_unpack_volume.py	Tests deadline handling, late artifacts, and logging.
src/​unpack_volume.py	Implements deadline-based polling and consolidated logging.
src/​constants.py	Defines the retry timeout and polling interval.

_{Review effort: Balanced}