Add CI workflow to validate YAML frontmatter in PRs

Adds a GitHub Actions workflow that validates frontmatter in agent,
skill, and command .md files changed by a PR. Checks:

- Agents: name and description are present and parseable
- Skills: description is present (required for Skill tool discovery)
- Commands: description is present and parseable

The workflow only runs when PRs touch files in agents/, skills/, or
commands/ directories, and only validates the changed files.

.github/scripts/validate-frontmatter.ts

@@ -0,0 +1,273 @@
+#!/usr/bin/env bun
+/**
+ * Validates YAML frontmatter in agent, skill, and command .md files.
+ *
+ * Usage:
+ *   bun validate-frontmatter.ts                    # scan current directory
+ *   bun validate-frontmatter.ts /path/to/dir       # scan specific directory
+ *   bun validate-frontmatter.ts file1.md file2.md  # validate specific files
+ */
+
+import { parse as parseYaml } from "yaml";
+import { readdir, readFile } from "fs/promises";
+import { basename, join, relative, resolve } from "path";
+
+// Characters that require quoting in YAML values when unquoted:
+// {} [] flow indicators, * anchor/alias, & anchor, # comment,
+// ! tag, | > block scalars, % directive, @ ` reserved
+const YAML_SPECIAL_CHARS = /[{}[\]*&#!|>%@`]/;
+const FRONTMATTER_REGEX = /^---\s*\n([\s\S]*?)---\s*\n?/;
+
+/**
+ * Pre-process frontmatter text to quote values containing special YAML
+ * characters. This allows glob patterns like **\/*.{ts,tsx} to parse.
+ */
+function quoteSpecialValues(text: string): string {
+  const lines = text.split("\n");
+  const result: string[] = [];
+
+  for (const line of lines) {
+    const match = line.match(/^([a-zA-Z_-]+):\s+(.+)$/);
+    if (match) {
+      const [, key, value] = match;
+      if (!key || !value) {
+        result.push(line);
+        continue;
+      }
+      // Skip already-quoted values
+      if (
+        (value.startsWith('"') && value.endsWith('"')) ||
+        (value.startsWith("'") && value.endsWith("'"))
+      ) {
+        result.push(line);
+        continue;
+      }
+      if (YAML_SPECIAL_CHARS.test(value)) {
+        const escaped = value.replace(/\\/g, "\\\\").replace(/"/g, '\\"');
+        result.push(`${key}: "${escaped}"`);
+        continue;
+      }
+    }
+    result.push(line);
+  }
+
+  return result.join("\n");
+}
+
+interface ParseResult {
+  frontmatter: Record<string, unknown>;
+  content: string;
+  error?: string;
+}
+
+function parseFrontmatter(markdown: string): ParseResult {
+  const match = markdown.match(FRONTMATTER_REGEX);
+
+  if (!match) {
+    return {
+      frontmatter: {},
+      content: markdown,
+      error: "No frontmatter found",
+    };
+  }
+
+  const frontmatterText = quoteSpecialValues(match[1] || "");
+  const content = markdown.slice(match[0].length);
+
+  try {
+    const parsed = parseYaml(frontmatterText);
+    if (parsed && typeof parsed === "object" && !Array.isArray(parsed)) {
+      return { frontmatter: parsed as Record<string, unknown>, content };
+    }
+    return {
+      frontmatter: {},
+      content,
+      error: `YAML parsed but result is not an object (got ${typeof parsed}${Array.isArray(parsed) ? " array" : ""})`,
+    };
+  } catch (err) {
+    return {
+      frontmatter: {},
+      content,
+      error: `YAML parse failed: ${err instanceof Error ? err.message : err}`,
+    };
+  }
+}
+
+// --- Validation ---
+
+type FileType = "agent" | "skill" | "command";
+
+interface ValidationIssue {
+  level: "error" | "warning";
+  message: string;
+}
+
+function validateAgent(
+  frontmatter: Record<string, unknown>
+): ValidationIssue[] {
+  const issues: ValidationIssue[] = [];
+
+  if (!frontmatter["name"] || typeof frontmatter["name"] !== "string") {
+    issues.push({ level: "error", message: 'Missing required "name" field' });
+  }
+  if (
+    !frontmatter["description"] ||
+    typeof frontmatter["description"] !== "string"
+  ) {
+    issues.push({
+      level: "error",
+      message: 'Missing required "description" field',
+    });
+  }
+
+  return issues;
+}
+
+function validateSkill(
+  frontmatter: Record<string, unknown>
+): ValidationIssue[] {
+  const issues: ValidationIssue[] = [];
+
+  if (!frontmatter["description"] && !frontmatter["when_to_use"]) {
+    issues.push({
+      level: "error",
+      message: 'Missing required "description" field',
+    });
+  }
+
+  return issues;
+}
+
+function validateCommand(
+  frontmatter: Record<string, unknown>
+): ValidationIssue[] {
+  const issues: ValidationIssue[] = [];
+
+  if (
+    !frontmatter["description"] ||
+    typeof frontmatter["description"] !== "string"
+  ) {
+    issues.push({
+      level: "error",
+      message: 'Missing required "description" field',
+    });
+  }
+
+  return issues;
+}
+
+// --- File type detection ---
+
+function detectFileType(filePath: string): FileType | null {
+  if (filePath.includes("/agents/")) return "agent";
+  if (filePath.includes("/skills/") && basename(filePath) === "SKILL.md")
+    return "skill";
+  if (filePath.includes("/commands/")) return "command";
+  return null;
+}
+
+// --- File discovery ---
+
+async function findMdFiles(
+  baseDir: string
+): Promise<{ path: string; type: FileType }[]> {
+  const results: { path: string; type: FileType }[] = [];
+
+  async function walk(dir: string) {
+    const entries = await readdir(dir, { withFileTypes: true });
+    for (const entry of entries) {
+      const fullPath = join(dir, entry.name);
+      if (entry.isDirectory()) {
+        await walk(fullPath);
+      } else if (entry.name.endsWith(".md")) {
+        const type = detectFileType(fullPath);
+        if (type) {
+          results.push({ path: fullPath, type });
+        }
+      }
+    }
+  }
+
+  await walk(baseDir);
+  return results;
+}
+
+// --- Main ---
+
+async function main() {
+  const args = process.argv.slice(2);
+
+  let files: { path: string; type: FileType }[];
+  let baseDir: string;
+
+  if (args.length > 0 && args.every((a) => a.endsWith(".md"))) {
+    baseDir = process.cwd();
+    files = [];
+    for (const arg of args) {
+      const fullPath = resolve(arg);
+      const type = detectFileType(fullPath);
+      if (type) {
+        files.push({ path: fullPath, type });
+      }
+    }
+  } else {
+    baseDir = args[0] || process.cwd();
+    files = await findMdFiles(baseDir);
+  }
+
+  let totalErrors = 0;
+  let totalWarnings = 0;
+
+  console.log(`Validating ${files.length} frontmatter files...\n`);
+
+  for (const { path: filePath, type } of files) {
+    const rel = relative(baseDir, filePath);
+    const content = await readFile(filePath, "utf-8");
+    const result = parseFrontmatter(content);
+
+    const issues: ValidationIssue[] = [];
+
+    if (result.error) {
+      issues.push({ level: "error", message: result.error });
+    }
+
+    if (!result.error) {
+      switch (type) {
+        case "agent":
+          issues.push(...validateAgent(result.frontmatter));
+          break;
+        case "skill":
+          issues.push(...validateSkill(result.frontmatter));
+          break;
+        case "command":
+          issues.push(...validateCommand(result.frontmatter));
+          break;
+      }
+    }
+
+    if (issues.length > 0) {
+      console.log(`${rel} (${type})`);
+      for (const issue of issues) {
+        const prefix = issue.level === "error" ? "  ERROR" : "  WARN ";
+        console.log(`${prefix}: ${issue.message}`);
+        if (issue.level === "error") totalErrors++;
+        else totalWarnings++;
+      }
+      console.log();
+    }
+  }
+
+  console.log("---");
+  console.log(
+    `Validated ${files.length} files: ${totalErrors} errors, ${totalWarnings} warnings`
+  );
+
+  if (totalErrors > 0) {
+    process.exit(1);
+  }
+}
+
+main().catch((err) => {
+  console.error("Fatal error:", err);
+  process.exit(2);
+});

.github/workflows/validate-frontmatter.yml

@@ -0,0 +1,34 @@
+name: Validate Frontmatter
+
+on:
+  pull_request:
+    paths:
+      - '**/agents/*.md'
+      - '**/skills/*/SKILL.md'
+      - '**/commands/*.md'
+
+jobs:
+  validate:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: oven-sh/setup-bun@v2
+
+      - name: Install dependencies
+        run: cd .github/scripts && bun install yaml
+
+      - name: Get changed frontmatter files
+        id: changed
+        run: |
+          FILES=$(gh pr diff ${{ github.event.pull_request.number }} --name-only | grep -E '(agents/.*\.md|skills/.*/SKILL\.md|commands/.*\.md)$' || true)
+          echo "files<<EOF" >> "$GITHUB_OUTPUT"
+          echo "$FILES" >> "$GITHUB_OUTPUT"
+          echo "EOF" >> "$GITHUB_OUTPUT"
+        env:
+          GH_TOKEN: ${{ github.token }}
+
+      - name: Validate frontmatter
+        if: steps.changed.outputs.files != ''
+        run: |
+          echo "${{ steps.changed.outputs.files }}" | xargs bun .github/scripts/validate-frontmatter.ts