The server now logs a loud warning at startup when the SQLCipher KDF is weakened below the production floor (reached only in test mode, e.g. ``LDR_TEST_MODE``) while user databases already exist. New databases would be created with this weak at-rest work factor, and — separately — any existing database created at a higher KDF can no longer be opened: its on-disk key is unchanged, but the server now derives a different, weaker key, so decryption fails and login returns a generic "Invalid username or password" 401 for every affected user (the KDF-mismatch symptom class behind PR #4775). Silent on fresh deployments and when the effective KDF is at/above the floor.
