- removed all logging of raw IV, JWK, session tokens, verification codes
→ logs now only include error codes, timestamps and short non-reversible SHA-256 hashes (first 4 bytes)
- replaced global master key storage with PBKDF2-derived non-extractable AES key
→ master key lives only in session memory and is cleared on timeout/focus-out
- added password-based derivation (PBKDF2) for master key initialization
- migrated persistent key storage to AES-GCM wrapped ciphertext in IndexedDB
→ JWK export → encrypt with session master key → store ciphertext + IV + metadata
→ unwrap + import as non-extractable on restore
- removed busy-wait loops and direct `window.gc()` calls
→ replaced with async non-blocking cleanup via setTimeout/Promise/WebWorker
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