[Aafimalek]

What does this PR do?

An expired prompt can start a background refresh while another operation invalidates or replaces its cache entry. If the old request finishes afterward, it can restore stale content or delete the newer entry after a 404.

Update or delete the cache entry only when it is still the same entry that scheduled the refresh. Foreground fetches retain their existing behavior.

Type of change

• Bug fix

Verification

uv run --frozen pytest -q tests/unit/test_prompt.py
uv run --frozen pytest -n 4 --dist worksteal tests/unit
uv run --frozen ruff check .
uv run --frozen ruff format --check .
uv run --frozen mypy langfuse --no-error-summary

The regression exercises a delayed successful response and a delayed 404, both after invalidation and after replacement with a newer entry. Before the fix, the successful response overwrote the newer prompt and the 404 deleted it. The full unit suite passed with 1,019 passed and 2 skipped, using local test credentials.

Checklist

• Diff reviewed against code_review.md.
• Regression tests added for both outcomes.
• Generated files and credentials excluded from the diff.

Confidence Score: 5/5

The PR appears safe to merge.

Summary

Background refreshes now change the cache only when the entry that started the refresh is still current. Foreground fetches keep their existing behavior.

• Background refreshes only change the cache entry that started them.

_{Reviews (2) · Last reviewed commit: "test(prompts): verify background refresh..." · Reviewed by Greptile}

[claude]

Claude Code Review

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