Auto-reload skills when updated by another session

Problem

When running multiple Claude Code sessions from the same project directory, skills updated in one session are not picked up by other running sessions. The only workaround is to restart the session, which loses conversation context.

Proposed Solution

Implement a filesystem-based notification mechanism for skill hot-reloading:

1. Maintain a skill checksum/version file (e.g., .claude/.skills-hash) that gets updated whenever a skill file is written
2. On each prompt or skill invocation, check if the hash file has changed since last read
3. If changed, reload skills from disk into the session context

This would be lightweight — a single stat() call per prompt to check mtime on the hash file, only doing the full reload when it actually changed.

Alternatives Considered

• --add-dir .claude enables live change detection, but only for that specific directory and requires launching with the flag
• Manual session restart works but loses conversation context
• A /reload-skills slash command would help but still requires manual intervention

Use Case

Running parallel Claude Code sessions on the same project — one session iterates on skill definitions while others use them. Common when developing/testing skills or when a team member updates shared project skills.