OS secure store per platform: macOS Keychain (/usr/bin/security), Windows Credential
Manager (advapi32 P/Invoke), Linux secret-tool; AES-256-CBC+HMAC encrypt-then-MAC
fallback (CI-safe, master secret + machine id via PBKDF2, ciphertext under user
app-data, never in repo). Env override (MCPFORUNITY_<P>_API_KEY, read-only) layered on
top; SecretRedactor scrubs auth tokens. Keys never touch EditorPrefs/bridge/logs/git.
EditMode tests for fallback round-trip, encryption-at-rest, env override, redaction.
Compiles clean on Unity 2021.3.45f2 (floor).
Claude-Session: https://claude.ai/code/session_01Tjpb5gYgUe2AUJuRdXr7Lv
Shutong Wu