[Aafimalek]

What does this PR do?

Prompt cache expiry rounds timestamps down to whole seconds and considers an item expired only when the rounded time is greater than its expiry. As a result, a positive TTL can be treated as fresh for almost one additional second. For example, an item cached at 100.75 seconds with a one-second TTL is still considered fresh at 101.75 seconds, so the usual stale-while-revalidate refresh is not scheduled at the configured expiry.

Keep fractional timestamp precision and treat the item as expired once the TTL has elapsed. The stale-while-revalidate behavior remains unchanged: the first request after expiry can still receive stale data while the background refresh runs.

This addresses positive-TTL timing; #2114 separately addresses writing to the cache when the caller explicitly requests a zero TTL.

Type of change

• Bug fix
• New feature
• Breaking change
• Refactor
• Documentation update
• Tooling, CI, or repo maintenance

Verification

• A deterministic test for the exact TTL boundary failed before the fix and passes afterward. The complete prompt unit file passed: 27 tests.
• ruff check ., ruff format --check ., mypy langfuse --no-error-summary, and the repository pre-commit hooks passed.
• Linux unit suite: 1,008 passed, two skipped, eight failed when LANGFUSE_TRACING_ENVIRONMENT=unit was set for the run. Those eight environment-propagation cases all passed when rerun with that variable unset. The entire unit suite was not rerun after changing the environment.
• No live provider or server E2E tests were run; this change affects local cache timing.

Checklist

• I self-reviewed the diff using code_review.md.
• I added or updated tests for behavior changes.
• I updated docs, examples, or .env.template if needed. (No documentation change was needed.)
• I did not hand-edit generated files; if generated files changed, I used the upstream regeneration path.
• I did not commit secrets or credentials.

Confidence Score: 5/5

The PR appears safe to merge.

Summary

Prompt cache entries now keep fractional timestamps and expire when their full TTL has elapsed.

• Prompt entries expire as soon as their full TTL elapses.

Aafimalek explicitly deferred zero-TTL cache writes to #2114.

_{Reviews (1) · Last reviewed commit: "fix(prompts): honor cache expiry at frac..." · Reviewed by Greptile}

[claude]

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