test(ids): align extractPurpose tests with refactored priority chain

The previous suite had a test "extracts from description field" that
fed a bare `description: ...` string and expected it to be matched.
That was exactly the body-level fallback regex that produced the
"Analyzes provided dataset" false purpose on component-creation-guide.md
(reported by CodeRabbit on PR #747). The refactor in this PR
intentionally removed that match, so the test must be updated to
reflect the new contract.

Changes to the test file:

* Replaced "extracts from description field" with two replacement tests:
  - "extracts from YAML frontmatter `description:` field" — feeds a
    `---\ndescription: X\n---` block and expects extraction from it.
  - "handles quoted YAML frontmatter description" — feeds
    `description: "X"` inside frontmatter and expects the quotes to
    be stripped.

* Added "falls back to ## Overview when no Purpose section" — covers
  the new strategy 3 in the priority chain (many guides like
  component-creation-guide.md use Overview instead of Purpose).

* Added TWO regression tests for the bug that motivated the refactor:
  - "does NOT match body-level `description:` outside frontmatter" —
    reproduces the exact component-creation-guide pattern (Overview
    section + a fenced code block with `Task description:` inside)
    and asserts the Overview wins.
  - "does NOT extract from `description:` lines without YAML
    frontmatter delimiters" — bare `description: X` without `---`
    delimiters falls through to the `# Title` header, NOT to the
    body line.

Test result: 79/79 pass. Existing 5 tests in the suite still pass.
Two new tests cover the YAML frontmatter branch (priority 1) and the
new `## Overview` branch (priority 3). Two regression tests lock in
the removal of the body-level matcher so it can't silently come back.

Author: rafaelscosta

tests/core/ids/populate-entity-registry.test.js

@@ -155,12 +155,24 @@ describe('populate-entity-registry (AC: 3, 4, 12)', () => {
       expect(purpose).toBe('This is the purpose line.');
     });
 
-    it('extracts from description field', () => {
-      const content = 'description: My awesome description here';
+    it('extracts from YAML frontmatter `description:` field', () => {
+      const content = '---\ndescription: My awesome description here\nversion: 1.0\n---\n\n# Title';
       const purpose = extractPurpose(content, '/test.md');
       expect(purpose).toBe('My awesome description here');
     });
 
+    it('handles quoted YAML frontmatter description', () => {
+      const content = '---\ndescription: "A quoted description"\n---\n\n# Title';
+      const purpose = extractPurpose(content, '/test.md');
+      expect(purpose).toBe('A quoted description');
+    });
+
+    it('falls back to ## Overview when no Purpose section', () => {
+      const content = '# Title\n\n## Overview\n\nThis guide walks you through X.\n\n## Other';
+      const purpose = extractPurpose(content, '/test.md');
+      expect(purpose).toBe('This guide walks you through X.');
+    });
+
     it('falls back to header', () => {
       const content = '# My Module Title\n\nSome content.';
       const purpose = extractPurpose(content, '/test.md');
@@ -177,6 +189,40 @@ describe('populate-entity-registry (AC: 3, 4, 12)', () => {
       const purpose = extractPurpose(longPurpose, '/test.md');
       expect(purpose.length).toBeLessThanOrEqual(200);
     });
+
+    // Regression test for the bug that motivated the priority-chain refactor:
+    // a body-level `description:` line inside example output or a code block
+    // used to be matched and treated as the doc's purpose. That was the source
+    // of `component-creation-guide.md` getting "Analyzes provided dataset" as
+    // its purpose (which was example installer transcript output, not a real
+    // description of the guide).
+    it('does NOT match body-level `description:` outside frontmatter', () => {
+      const content = [
+        '# Component Creation Guide',
+        '',
+        '## Overview',
+        '',
+        'This guide walks you through creating components.',
+        '',
+        '## Example Output',
+        '',
+        '```',
+        '? Task description: Analyzes provided dataset to identify patterns',
+        '```',
+      ].join('\n');
+      const purpose = extractPurpose(content, '/test.md');
+      // Should pick up Overview section, NOT the body-level "description:"
+      expect(purpose).toBe('This guide walks you through creating components.');
+      expect(purpose).not.toContain('Analyzes');
+    });
+
+    it('does NOT extract from `description:` lines without YAML frontmatter delimiters', () => {
+      const content = 'description: This should not be matched\n\n# Title';
+      const purpose = extractPurpose(content, '/test.md');
+      // No `---` delimiters → not frontmatter → falls through to `# Title`
+      expect(purpose).toBe('Title');
+      expect(purpose).not.toContain('This should not');
+    });
   });
 
   describe('detectDependencies()', () => {