Dynamically reload skills and notify the model at turn boundaries

[danielkov]

Summary

Skills can change while a Kit session is running, including project/user skills and skills supplied by mutable local Agent Plugins. A live session should discover those changes without requiring a process restart.

Environment

• Kit: 0.1.119
• OS: macOS (Darwin, arm64)
• Host: Kit ACP session

Requested behavior

• Watch or re-scan configured skill sources for added, changed, and removed skills.
• Rebuild the effective skill catalog using the existing precedence rules.
• Apply updates at a turn boundary rather than mutating the catalog midway through a model turn.
• Notify the model through the next existing turn when a change is detected, rather than creating an unsolicited background turn.
• Keep the notification bounded and identify which skill names were added, changed, or removed.
• If an update is invalid, retain the last valid skill catalog and surface a diagnostic.

This would make skill updates immediately useful while preserving deterministic behavior within each turn.