fix(registries): resolve GitLab marketplace plugins

[Minitour]

Summary

Plugins from GitLab's marketplace (gitlab-org/ai/skills) failed with "Plugin subpath not found". There were two bugs; this PR fixes both. Closes #312.

What changed

Leading dot stripped twice

• The marketplace lists ./.claude-plugin/plugins/glab. The parser stripped ./, then the path join stripped a leading . again, so capa looked for claude-plugin/plugins/glab.
• Only a leading ./ (or a bare .) is stripped now. Fixed in the generic claude-marketplace parser and the bundled claude-plugins adapter, with its pin updated in bundled.ts.

Symlinked plugin skills

• In that repo, each plugin's skills/<name> is a symlink to the repo's top-level skills/<name>.
• Skill discovery skipped symlinked dirs, so the plugin had no skills and resolution failed with "No plugin manifest found".
• The stable plugin copy used cpSync, which keeps the relative link, and the link breaks once copied.
• Discovery (getSkillEntriesFromPath) now accepts symlinked skill dirs.
• The stable plugin copy now goes through copySkillTree with the snapshot as the root:
  • Symlinks are replaced by what they point to when they resolve inside the cloned repo.
  • Links that point outside it are still rejected.
  • There is no per-file size cap, matching the old cpSync behavior.
• copySkillTree decided file vs directory from lstat, so it silently dropped every symlink. It now follows contained links and skips links back to an enclosing directory, so a cycle can't recurse forever.

Review follow-ups

• Link fan-out: links pointing at each other used to copy 2^N trees. The copy now walks the real tree first, then follows links, and enters each real directory once. A link to a directory that was already copied is skipped, and a real directory always lands at its own path.
• Bad links: the plugin copy skips broken links, and links leaving the repository, with an install warning instead of failing the whole plugin.
• Stamp: the stable-copy stamp is versioned (copy-v2), so plugins copied by the old cpSync path are copied again once.
• Preview: the marketplace plugin preview checks the subpath with assertSafeRepoPath, like install does.

Notes

• On Windows without Developer Mode, git checks symlinks out as plain text files, so plugins built from symlinks still can't be installed there. The reporter is on Linux.
• Projects that already saved the stripped path (claude-plugin/plugins/...) in capabilities.yaml need to re-add the plugin or fix the path.

Test plan

• Marketplace test: ./.claude-plugin/..., .agents/... and . map to the right subpaths.

• copySkillTree test (junctions, so it also runs on Windows):

  • a symlinked dir inside root is copied;
  • the same copy without root is rejected;
  • a link cycle terminates.

• Integration test of GitLab's layout:

  • detectAndParseManifest finds the linked skill;
  • ensureStablePluginCopy writes a real directory.

  The test fails without the fix.

• Windows build, isolated HOME, real gitlab-org/ai/skills: the subpath now resolves. The symlinked skill couldn't be checked end to end on this machine, because Windows checks the links out as text files.

• exec bits preserved by the new copy path on Linux (checked with a compiled Linux binary).

• bunx tsc --noEmit. On Windows the full suite fails only on the usual EBUSY temp cleanup and on symlink creation without privilege.

Checklist

• Tests added or updated
• bunx tsc --noEmit passes
• Docs updated (if user-facing): not needed

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