fix(idempotency): compute the Redis orphan lock timeout from the configured expiry - #8779

Summary

The Redis/Cache orphan lock timeout was computed in CachePersistenceLayer.__init__, right after super().__init__() had set expires_after_seconds to its 3600-second default. min(10, 3600) therefore always produced 10, and the later configure() call — which applies the user's IdempotencyConfig — never changed it. A lock could outlive the record it protects when expires_after_seconds was below 10, leaving later calls unable to take over an orphaned record.

The timeout is now computed at the point of use in _acquire_lock, from self.expires_after_seconds after configuration. The 10-second cap is preserved for longer expiries.

Test

Added test_orphan_lock_ttl_follows_configured_expiry in tests/functional/idempotency/_redis/test_redis_layer.py. It drives the public idempotent decorator with a fake Redis client that records the ex argument of every set call, seeds an expired INPROGRESS record, and checks the ex used for the :lock key:

• expires_after_seconds=2 -> lock ex=2 (was 10 before the fix)
• expires_after_seconds=30 -> lock ex=10 (cap unchanged)

Verification run locally (terminal output):

$ uv run pytest tests/functional/idempotency/_redis/test_redis_layer.py -k orphan_lock_ttl -q
# before the fix
FAILED ... test_orphan_lock_ttl_follows_configured_expiry[2-2]
E       AssertionError: lock ex=10, want 2
=========== 1 failed, 1 passed, 31 deselected ============

# after the fix
================= 2 passed, 31 deselected =================

• Full Redis functional test file: 33 passed.
• ruff format aws_lambda_powertools tests examples --check: 1398 files already formatted; ruff check aws_lambda_powertools tests examples: All checks passed!.
• mypy on the changed source: Success: no issues found in 1 source file.
• All idempotency unit + functional tests: uv run pytest tests/functional/idempotency tests/unit/idempotency -q -> 210 passed.
• The full unit + functional suite was also run. Two unrelated tests (auth_alpha/oauth2 timing and event_handler/_pydantic PurePath encoding) fail on this Windows/Python 3.14 setup; I confirmed both fail identically on an unmodified develop checkout, so they are pre-existing environment failures, not regressions from this change.

By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of your choice.

Disclaimer: We value your time and bandwidth. As such, any pull requests created on non-triaged issues might not be successful.

closes #8726