🤖 bug: support symlinked project skills in local workspaces

[ThomasK33]

Summary

Mux currently treats symlinked project skills under .mux/skills/* as invalid in host-local project workspaces. That means skills installed as symlinks do not show up in agent_skill_list and cannot be managed through agent_skill_write / Chat with Mux.

Background

In the workflow used for PR #2910, the project skill entries were installed as symlinks. Codex flagged that local project skill discovery and management currently reject those symlinked entries, so the right follow-up is to teach Mux to support this installation pattern rather than forcing individual PRs to replace symlinks with copied directories.

Problem

• agent_skill_list skips symbolic-link entries for project scope.
• agent_skill_write / the skill file utilities reject symlinked project skill directories.
• As a result, symlinked project skills do not appear or remain manageable through Chat with Mux in the default host-local context (non-SSH / non-docker).

References

• Codex review comment: 🤖 feat: add browser automation skills and docs #2910 (comment)
• PR: 🤖 feat: add browser automation skills and docs #2910
• Relevant code paths called out in the review: src/node/services/tools/agent_skill_list.ts, src/node/services/tools/agent_skill_write.ts, and src/node/services/agentSkills/skillFileUtils.ts.

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Generated with mux • Model: openai:gpt-5.4 • Thinking: high

[ThomasK33]

Note: the skills CLI by Vercel defaults to installing skills into .agents/skills/ and then symlinking these to the corresponding agent folders.