feat: [gh skill CLI, v2.90.0+] session-start skill sync in Cowork — part of cross-surface remote skill integration (#50148)

Part of the cross-surface gh skill integration proposed in #50148. This issue covers Cowork sessions specifically.

The surface

Cowork sessions are ephemeral — there is no persistent local filesystem between sessions. Skills must be loaded at session start to be available as commands, and currently there is no native mechanism for loading them from a remote source.

What's missing today

Users who maintain skills in a GitHub repo must author a bootstrap skill that installs other skills and invoke it manually at the start of every session. The pattern works but is invisible to the runtime, breaks silently if skipped, and cannot share config state with the Claude.ai customize panel or Claude Code CLI settings.

The ask for this surface

Honor the skills.sources config established in #50148 at Cowork session initialization — syncing declared repos via the gh skill protocol before the first user turn, with no manual invocation required. Skills should appear as commands immediately in the session, consistent with how they appear in Claude Code and the customize panel.

For shared Cowork workspaces, a workspace-level skills.sources config would let all workspace members get the same skill set without individual setup — particularly relevant for teams using Cowork as a shared environment.

How it connects to other surfaces

The remote source configured in the Claude.ai customize panel (#50154) or in Claude Code settings.json (#50150) should be the same source Cowork reads from — one configuration that follows you across surfaces. Managed sources from enterprise admins (issue to follow) should apply to Cowork workspaces the same way they apply to other surfaces. The full cross-surface picture is in #50148.

References

• Cross-surface parent: #50148
• gh skill announcement: https://github.blog/changelog/2026-04-16-manage-agent-skills-with-github-cli/