fix(skills): extend CRLF fence handling to stripFrontmatter + derived-manifest name parse

Same root cause as the parent commit, two sibling LF-only fence regexes:
- src/core/skill-brain-first.ts FRONTMATTER_RE: on CRLF skills,
  stripFrontmatter was a no-op, so a frontmatter 'tools: [web_search]'
  leaked into the body scan and false-flagged the skill (the exact F6
  case the code comments guard against). Regression test added.
- src/core/skill-manifest.ts parseSkillName: derived-manifest mode
  (no manifest.json) fell back to the dirname for CRLF skills instead
  of the frontmatter name.

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

src/core/skill-brain-first.ts

@@ -162,9 +162,11 @@ export const PHASE_HEADING_RE = /^##+\s*(?:Phase\s*1|Step\s*0)\b[^\n]*brain/im;
 /**
  * Frontmatter fence regex used by body extraction. Conservative match:
  * leading `---\n` through the next `\n---` (greedy stop). Matches the
- * shape `parseSkillFrontmatter` already accepts.
+ * shape `parseSkillFrontmatter` already accepts, including CRLF fences —
+ * if this stayed LF-only, a CRLF skill's `tools: [web_search]` frontmatter
+ * would survive into the body scan and false-flag the skill (F6).
  */
-const FRONTMATTER_RE = /^---\n[\s\S]*?\n---\n?/;
+const FRONTMATTER_RE = /^---\r?\n[\s\S]*?\r?\n---\r?\n?/;
 
 // ---------------------------------------------------------------------------
 // Hardcoded EXEMPT_SKILLS (CMT1 — replaces the dropped upgrade migration)

src/core/skill-manifest.ts

@@ -47,7 +47,7 @@ export interface ManifestLoadResult {
 function parseSkillName(skillMdPath: string): string | null {
   try {
     const content = readFileSync(skillMdPath, 'utf-8');
-    const fmMatch = content.match(/^---\n([\s\S]*?)\n---/);
+    const fmMatch = content.match(/^---\r?\n([\s\S]*?)\r?\n---/);
     if (!fmMatch) return null;
     const fm = fmMatch[1];
     // Match `name: foo` or `name: "foo"` or `name: 'foo'`

test/skill-brain-first.test.ts

@@ -227,6 +227,20 @@ describe('stripFrontmatter', () => {
     // Body should NOT contain `web_search` (it was in the stripped frontmatter).
     expect(body.includes('web_search')).toBe(false);
   });
+
+  test('F6 holds for CRLF fences — frontmatter tools do not leak into the body scan', () => {
+    const content = [
+      '---',
+      'name: x',
+      'tools: [web_search]',
+      '---',
+      '',
+      '# x',
+      'Body says gbrain search comes first.',
+    ].join('\r\n');
+    const body = stripFrontmatter(content);
+    expect(body.includes('web_search')).toBe(false);
+  });
 });
 
 describe('offset helpers', () => {