Skills fail to load in GitHub Copilot CLI 1.0.65+ due to array-shaped argument-hint #514

Summary

One or more SKILL.md frontmatters in this repo declare argument-hint: with bare YAML brackets, e.g. argument-hint: [X]. YAML parses that as a one-element flow-sequence (a list), not a string. GitHub Copilot CLI 1.0.65 tightened its skill-loader to require argument-hint to be a string, so on 1.0.65+ these skills silently fail to load — no error is surfaced to the user, they just don't appear in copilot skill list or the slash-command menu.

Same class of latent bug on Claude Code — see anthropics/claude-code#22161 (accepts either shape today, but the documented contract is a string).

Why bare brackets are a bug

Per YAML 1.2, a value starting with an unquoted [ opens a flow-sequence node:

argument-hint: [X]      # → list ['X']       ❌
argument-hint: "[X]"    # → string '[X]'     ✅
argument-hint: ["X"]    # → list ['X']       (STILL a list — quoting inside the brackets doesn't help)

Verifiable with any YAML 1.2 parser:

python3 -c 'import sys, yaml; fm = yaml.safe_load(open(sys.argv[1]).read().split("---")[1]); print(type(fm["argument-hint"]).__name__)' path/to/SKILL.md
# → list

Reproducer

1. Install / upgrade to GitHub Copilot CLI 1.0.65 or later
2. Install this plugin / skill pack
3. Run copilot skill list — the affected skill(s) will be missing with no error

Documented contract — string

• VS Code Agent Skills docs — argument-hint documented as a string
• Copilot CLI Skills tutorial (copilot-cli-for-beginners/05-skills) — every example wraps the value in double quotes
• Copilot CLI 1.0.65 release notes — skill-loader tightening enforcing the string type

Fix

Two-character fix per file — wrap the value in double quotes. Full patch in #513.

Broader context

Copilot CLI 1.0.65 dropped recently and about 30 other public agent-skills repos ship the same bug shape — the surface hasn't caught up yet.