- Added metadata merge helpers in `sdk/cliproxy/auth` to retain existing auth-file settings while excluding token lifecycle fields.
- Applied merge before saving in management handler and `sdk/auth.Manager.Login` so re-login overwrites credentials without discarding user-configured fields.
- Updated token save paths for Claude, Codex, Kimi, XAI, and Vertex to persist merged metadata payloads when writing auth files.
Closes: #4945