Expert skills in the chat session were derived by intersecting built-in
experts with ACP availableCommands, which caused Codex experts to never
appear since Codex does not advertise skills through ACP.
- Add `experts_list_for_agent` backend API that checks symlink status
across all global skill dirs for the given agent type
- Replace availableCommands-based expert filtering with symlink-based
query, making the settings page the single source of truth
- Use `$` prefix for Codex expert skills while keeping `/` for slash
commands and other agents' experts
- Disable the expert button when no experts are linked for the agent
- Invalidate per-agent expert cache after link/unlink in settings
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
ade59f474c