ci: validate against the official Claude Code plugin schema

Add a `spec` job to the Validate plugins workflow that installs the
Claude Code CLI (pinned to 2.1.173 — schema warnings can change between
releases, so bumps should be deliberate) and runs
`claude plugin validate .` offline.

Phase 1 of #4: the command exits 0 on warnings, so this lands green on
current main (1 known warning: `stability` in one plugin.json) while
failing on real schema errors — manifest typos, malformed hooks.json,
bad skill frontmatter — and future spec drift. Phase 2 (--strict) comes
once the `stability` field question is settled.

Closes #4

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Author: wzslr321

.github/workflows/validate-plugins.yml

@@ -25,3 +25,25 @@ jobs:
 
       - name: Validate plugin structure
         run: go run ./cmd/validate-plugins
+
+  spec:
+    name: Claude Code plugin spec check
+    runs-on: ubuntu-latest
+    timeout-minutes: 5
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Setup Node
+        uses: actions/setup-node@v4
+        with:
+          node-version: 22
+
+      # Pinned: schema warnings can change between CLI releases; bump deliberately.
+      - name: Install Claude Code CLI
+        run: npm install -g @anthropic-ai/claude-code@2.1.173
+
+      # Phase 1: fails on schema errors only; warnings pass (exit 0).
+      # Phase 2: add --strict once the manifest cleanup lands — see issue #4.
+      - name: Validate against the Claude Code plugin schema
+        run: claude plugin validate .

AGENTS.md

@@ -46,7 +46,7 @@ Validate plugin structure locally with Go:
 go run ./cmd/validate-plugins
 ```
 
-CI runs the same structure validation plus Go formatting/lint on every PR. After pushing, watch CI with `gh pr checks <pr-number>`.
+CI runs the same structure validation, Go formatting/lint, and the official Claude Code plugin-spec check (`claude plugin validate .`, errors-only for now) on every PR. After pushing, watch CI with `gh pr checks <pr-number>`.
 
 ## Platform notes