Cryptext x64 0.8 regression checklist
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1. Encrypt/decrypt: 0 B, 1 B, 4 MiB, 4 MiB+1, >300 MiB.
2. Keep-original checked in both directions -> source remains.
3. Keep-original unchecked in both directions -> source removed only after success.
4. Remember mode: first password entry works; second operation works with blank edit.
5. Switch to forget mode -> blank edit must no longer reuse cached password.
6. Wrong remembered password on decrypt -> auth error + cache invalidation.
7. One-byte ciphertext modification -> auth error; no final plaintext.
8. Existing target/temp -> no overwrite.
9. Session and active password buffers are wiped on process exit by code inspection.
