fix(apple): don't evict caches during protection-class migration#162
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…ction-class migration decrypt_with_cached_key re-stores the wrapping key on every cache miss to migrate items to AfterFirstUnlockThisDeviceOnly. It called keychain_store(), which evicts both the wrapping-key cache and the LAContext registry. This created a self-perpetuating cycle: every sign saw a cache miss, triggered the migration, evicted both caches, and forced a fresh Touch ID prompt on the next sign. Extract keychain_store_ffi (the raw FFI call without eviction) and use it in the migration path. The key bytes are unchanged — only the protection class is updated — so the cached entries remain valid. keychain_store retains the eviction for callers that change key bytes (generate_and_wrap, relabel_wrapping_key). Restores single-prompt-per-cache-window behavior: first sign triggers Touch ID, subsequent signs within the TTL reuse the cached LAContext.
This was referenced May 21, 2026
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Summary
decrypt_with_cached_keycalledkeychain_store()on every cache miss, which evicts both the wrapping-key cache and the LAContext registrykeychain_store_ffi(raw FFI, no eviction) and use it in the migration path — the key bytes are unchanged, so cached entries remain validkeychain_storeretains eviction for callers that change key bytes (generate, relabel)Root cause
PR #158 added a lazy protection-class migration that re-stores the wrapping key on cache miss. The re-store called
keychain_store()→cache_evict()→ nuked both the wrapping-key cache and LAContext registry. Next sign saw another cache miss → migration fired again → infinite cycle. Every sign got a fresh LAContext and Touch ID prompt.Test plan
cargo test --workspace— all existing tests passcargo clippy --workspace --all-targets -- -D warnings— cleancargo fmt --all -- --check— clean