feat: add shared/gh-skill.md workflow for gh skill install

.github/workflows/shared/gh-skill.md

@@ -0,0 +1,153 @@
+---
+# gh skill - Install Agent Skills
+# Installs agent skills from GitHub repositories using `gh skill install`
+# before the AI agent starts.
+#
+# Requirements:
+#   GitHub CLI v2.90.0 or later (for `gh skill` support)
+#
+# Documentation: https://cli.github.com/manual/gh_skill_install
+#
+# Usage:
+#   imports:
+#     - uses: shared/gh-skill.md
+#       with:
+#         skills:
+#           - github/awesome-copilot/documentation-writer
+#           - github/awesome-copilot/code-review
+#
+# Skill format:
+#   - owner/repo                     — install all skills from the repository
+#   - owner/repo/skill-name          — install a specific skill (latest)
+#   - owner/repo/skill-name@version  — install a pinned version
+
+import-schema:
+  skills:
+    type: array
+    items:
+      type: string
+    required: true
+    description: >
+      List of skills to install. Each entry is in the format owner/repo,
+      owner/repo/skill-name, or owner/repo/skill-name@version.
+      Examples: "github/awesome-copilot", "github/awesome-copilot/documentation-writer",
+      "github/awesome-copilot/code-review@v1.2.0"
+
+pre-agent-steps:
+  - name: Install agent skills
+    env:
+      GH_TOKEN: ${{ secrets.GH_AW_PLUGINS_TOKEN || secrets.GH_AW_GITHUB_TOKEN || secrets.GITHUB_TOKEN }}
+      GH_AW_SKILLS: ${{ github.aw.import-inputs.skills }}
+    run: |
+      set -euo pipefail
+      skills_json="${GH_AW_SKILLS}"
+      count=$(echo "$skills_json" | jq 'length')
+      if [ "$count" = "0" ]; then
+        echo "::error::shared/gh-skill.md import provided no skills. Add skills: <list> in the with: block."
+        exit 1
+      fi
+      agent="${AI_AGENT:-github-copilot}"
+      printf "::notice::Installing %d skill(s) for agent: %s\n" "$count" "$agent"
+      while IFS= read -r skill_entry; do
+        repo=$(echo "$skill_entry" | cut -d'/' -f1,2)
+        skill_part=$(echo "$skill_entry" | cut -d'/' -f3-)
+        if [ -n "$skill_part" ]; then
+          echo "Installing skill: $repo $skill_part"
+          gh skill install "$repo" "$skill_part" --agent "$agent"
+        else
+          echo "Installing all skills from: $repo"
+          gh skill install "$repo" --agent "$agent"
+        fi
+      done < <(echo "$skills_json" | jq -r '.[]')
+---
+
+<!--
+## Agent Skills
+
+This shared workflow installs agent skills before the AI agent runs, using the
+[`gh skill install`](https://cli.github.com/manual/gh_skill_install) command
+(available in GitHub CLI v2.90.0+).
+
+### How it works
+
+Each skill in the `skills:` list is installed into the repository's
+`.github/skills/` directory via `gh skill install`, making the skills available
+to the AI agent during its session.
+
+The target agent host is determined from the `AI_AGENT` environment variable if
+set (for example, Claude Code automatically sets `AI_AGENT=claude-code` for its
+subprocesses), otherwise defaults to `github-copilot`. Set `AI_AGENT` in your
+workflow's `agent.env` block to override:
+
+```yaml
+agent:
+  env:
+    AI_AGENT: claude-code
+```
+
+### Usage
+
+```yaml
+imports:
+  - uses: shared/gh-skill.md
+    with:
+      skills:
+        - github/awesome-copilot/documentation-writer
+        - github/awesome-copilot/code-review@v1.2.0
+```
+
+### Skill format
+
+Each entry in `skills:` is one of:
+
+| Format | Example | Effect |
+|--------|---------|--------|
+| `owner/repo` | `github/awesome-copilot` | Installs all skills from the repo |
+| `owner/repo/skill-name` | `github/awesome-copilot/documentation-writer` | Installs a specific skill (latest) |
+| `owner/repo/skill-name@version` | `github/awesome-copilot/code-review@v1.2.0` | Installs a pinned version |
+
+### Authentication
+
+Uses a token from the standard precedence chain:
+`GH_AW_PLUGINS_TOKEN` → `GH_AW_GITHUB_TOKEN` → `GITHUB_TOKEN`.
+
+For private skill repositories, configure `GH_AW_PLUGINS_TOKEN` or
+`GH_AW_GITHUB_TOKEN` with appropriate access.
+
+### Agent targeting
+
+The `AI_AGENT` environment variable controls which agent host receives the
+installed skills:
+
+- `AI_AGENT=github-copilot` — GitHub Copilot (default when unset)
+- `AI_AGENT=claude-code` — Claude Code
+- `AI_AGENT=cursor` — Cursor
+- `AI_AGENT=codex` — OpenAI Codex
+- `AI_AGENT=gemini-cli` — Gemini CLI
+
+Set `AI_AGENT` in `agent.env` to match the engine used by the workflow:
+
+```yaml
+engine: claude
+agent:
+  env:
+    AI_AGENT: claude-code
+imports:
+  - uses: shared/gh-skill.md
+    with:
+      skills:
+        - github/awesome-copilot/documentation-writer
+```
+
+### Network access
+
+`gh skill install` downloads skill files from GitHub. No additional network
+configuration is needed on standard GitHub-hosted runners. If your workflow
+uses a strict network firewall, add `github.com` to the allowed domains:
+
+```yaml
+network:
+  allowed:
+    - github.com
+```
+-->