Plugin skill silently dropped from /skills list despite "Installed N skills" confirming load

[shinyay]

Describe the bug

Installing my plugin shinyay/tokopt-skills (9 skills + 2 agents) reports Installed 9 skills, and copilot plugin list confirms registration, but /skills list consistently shows only 8 of the 9 skills. The missing skill is exactly the same one every time: slim-apply. The other 8 (antipattern-scan, heavy-tail, hygiene-coach, prompt-anatomy, prompt-optimizer, slim-rewind, slim-suggest, token-audit) appear correctly.

Verified:

• ✅ On disk: ~/.copilot/installed-plugins/_direct/shinyay--tokopt-skills/skills/slim-apply/SKILL.md exists, well-formed (3452 B, ASCII frontmatter, no BOM)
• ✅ Install log says Installed 9 skills → loader sees it
• ❌ /skills list shows 8/9 → display/filter layer drops one
• ❌ Cwd-shadowing ruled out — same result from /tmp (outside repo) and from inside the repo
• ❌ Description length ruled out — slim-apply is 346 chars, well within range of visible skills (233–357 chars)
• ❌ Frontmatter formatting ruled out — identical structure (just name: + description:) to the 8 visible skills

Repro repo: https://github.com/shinyay/tokopt-skills (public, v0.1.0)

Affected version

GitHub Copilot CLI 1.0.55-6.

Steps to reproduce the behavior

copilot plugin install shinyay/tokopt-skills
# → "Plugin "tokopt-skills" installed successfully. Installed 9 skills."

copilot plugin list | grep tokopt
# → "  • tokopt-skills (v0.1.0)"

ls ~/.copilot/installed-plugins/_direct/shinyay--tokopt-skills/skills/
# → 9 entries including slim-apply/

Then in an interactive copilot session:

/skills list

Count entries in the plugin: section that belong to tokopt-skills. Result: 8 entries, slim-apply missing.

Expected behavior

/skills list should show all 9 skills from the plugin, including slim-apply, matching the loader's Installed 9 skills count.

Additional context

Workarounds attempted (none worked):

1. Uninstall + reinstall — same 8/9
2. Edited SKILL.md to rename ## DO NOT → ## Guardrails and Destructive. → Note: (in case a safety-keyword filter was matching) — still 8/9
3. Cleared a stale duplicate directory _direct/tokopt-skills/ left over from an earlier local-path install — caused all 9 to disappear; re-established via symlink to recover the 8/9 state (separate-but-related quirk: the loader appears to resolve plugin dir by plugin-manifest name, not by <org>--<repo> directory name)

Description content of slim-apply (in case the filter is keyword-based):

Apply tokopt slim's compression IN-PLACE after the user has reviewed a slim-suggest preview AND explicitly approved. Writes compressed output back to disk with full safety: requires clean git tree, refuses symlinks, detects races. Use ONLY when the prior turn ran slim-suggest for the SAME single file. Never for first-pass analysis.

It is the only skill in the plugin whose description references another skill by name (slim-suggest, twice). Could /skills list be deduplicating or filtering based on cross-references in descriptions?

Environment:

• OS: Linux (WSL2, kernel 6.6.114.1-microsoft-standard)
• Arch: x86_64
• Node: v22.22.0
• Shell: bash
• Terminal: VS Code Insiders integrated terminal

Related quirk (separate finding from the same investigation):

When a plugin is installed from a GitHub repo shorthand (e.g., copilot plugin install shinyay/tokopt-skills), the plugin is unpacked to ~/.copilot/installed-plugins/_direct/shinyay--tokopt-skills/, but /skills list only sees the skills if a _direct/<plugin-manifest-name>/ directory (without the <org>-- prefix) is also present. Removing the orphan unprefixed directory leaves only the prefixed one, and the loader then loads 0 skills from the plugin, even though copilot plugin list still reports it as installed. A symlink _direct/tokopt-skills -> shinyay--tokopt-skills restores the loader. This suggests the plugin-name → directory resolution may not be handling the gh-shorthand naming convention consistently.