Changes
- Distinguish side sessions with a synchronized blue border pulse while preserving the purple travelling Ultracode border.
- Isolate side-session activity and usage from inherited parent subagent, background, scheduled, and monitor state while retaining context and session-owned tasks.
- Clarify Ctrl+C behavior for side sessions.
Validation
Targeted pager and shell tests passed, minimal cargo check passed, binary cargo build passed, and an actual PTY check passed for side entry, border pulse, 72x24 resize, busy cancellation staying in the side session, and Ctrl+C returning to the parent. git diff --check passed. Full test suite was not run.