- Added a new ultrathink mode module with standalone, case-insensitive detection, rainbow editor highlighting, and a hidden notice payload.
- Updated `CustomEditor` and the shared TUI `Editor` to support optional zero-width text decoration and apply the `ultrathink` styling during input rendering.
- Extended `AgentSession` prompt handling to append the hidden ultrathink notice after user turns in both streaming and non-streaming message flows, excluding synthetic messages.