feat: add Memcached backend with pymemcache HashClient#67
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- MemcachedBackend implementing BaseBackend protocol (get/set/delete/exists/health_check) - pymemcache HashClient for consistent hashing across multiple servers - TTL clamped to 30-day Memcached maximum (2,592,000 seconds) - MemcachedBackendConfig with pydantic-settings (CACHEKIT_MEMCACHED_ env prefix) - Error classification mapping pymemcache exceptions to BackendErrorType - Lazy import via __getattr__ (pymemcache is optional dependency) - 79 unit/config/critical tests (all mocked — integration tests to follow)
Bug fix: health_check() called self._client.stats() but HashClient has no stats() method — only Client does. Replaced with a benign get() probe. The unit tests never caught this because they mocked everything. This is exactly why integration tests matter. Integration tests (28 total, all against real Memcached): - CRUD round-trip: set/get/delete/exists, overwrite, empty values - TTL expiry: real server-side eviction, negative TTL, 30-day clamp - Key prefix isolation: namespace separation verified - Binary data integrity: null bytes, all-byte-values, 1MB payloads - Concurrent thread safety: 10 threads x 50 ops, mixed read/write/delete - Health check: live server + unreachable server - Decorator integration: @cache.minimal with set_default_backend - Edge cases: 500-key bulk ops, rapid set/delete cycles Threading note: per-thread MemcachedBackend instances used for concurrency tests — pymemcache HashClient pool has known contention issues when shared across many threads simultaneously.
Was missing from BACKEND_CONFIGS parametrization — never added when the memcached backend was created.
- Bump requests>=2.33.0 (CVE-2026-25645) in dev deps with py>=3.10 marker - Ignore pygments GHSA-5239-wwwm-4pmq in pip-audit (no upstream fix) - Validate server port is numeric and in range 1-65535 - Route health_check probe through _prefixed_key() for consistency
- Add error-raising tests for get/set/delete/exists except branches - Add __getattr__ lazy import tests for MemcachedBackend and unknown attr
CI PRs only run tests/critical/ for coverage. Added error paths, health_check failure, TTL clamping, key prefix, error classification, lazy import, and config validation to critical tests.
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Summary
health_check()was callingHashClient.stats()which doesn't exist — replaced with benignget()probeTest plan