test: add deterministic contributor mode preamble validation

40 new skill-validation tests (4 checks × 10 skills) verify:
- 0-10 rating scale present
- Calibration example present
- "What would make this a 10" field present
- Periodic reflection (not per-command)

Update existing E2E contributor eval for new report format.

test/skill-e2e.test.ts

@@ -323,10 +323,13 @@ File a contributor report about this issue. Then tell me what you filed.`,
     const logFiles = fs.readdirSync(logsDir).filter(f => f.endsWith('.md'));
     expect(logFiles.length).toBeGreaterThan(0);
 
+    // Verify new reflection-based format
     const logContent = fs.readFileSync(path.join(logsDir, logFiles[0]), 'utf-8');
     expect(logContent).toContain('Hey gstack team');
     expect(logContent).toContain('What I was trying to do');
     expect(logContent).toContain('What happened instead');
+    expect(logContent).toMatch(/rating/i);
+    expect(logContent).toMatch(/what would make/i);
 
     // Clean up
     try { fs.rmSync(contribDir, { recursive: true, force: true }); } catch {}

test/skill-validation.test.ts

@@ -438,6 +438,44 @@ describe('v0.4.1 preamble features', () => {
   }
 });
 
+// --- Contributor mode preamble structure validation ---
+
+describe('Contributor mode preamble structure', () => {
+  const skillsWithPreamble = [
+    'SKILL.md', 'browse/SKILL.md', 'qa/SKILL.md',
+    'qa-only/SKILL.md',
+    'setup-browser-cookies/SKILL.md',
+    'ship/SKILL.md', 'review/SKILL.md',
+    'plan-ceo-review/SKILL.md', 'plan-eng-review/SKILL.md',
+    'retro/SKILL.md',
+  ];
+
+  for (const skill of skillsWithPreamble) {
+    test(`${skill} has 0-10 rating in contributor mode`, () => {
+      const content = fs.readFileSync(path.join(ROOT, skill), 'utf-8');
+      expect(content).toContain('0 to 10');
+      expect(content).toContain('My rating');
+    });
+
+    test(`${skill} has calibration example`, () => {
+      const content = fs.readFileSync(path.join(ROOT, skill), 'utf-8');
+      expect(content).toContain('Calibration');
+      expect(content).toContain('the bar');
+    });
+
+    test(`${skill} has "what would make this a 10" field`, () => {
+      const content = fs.readFileSync(path.join(ROOT, skill), 'utf-8');
+      expect(content).toContain('What would make this a 10');
+    });
+
+    test(`${skill} uses periodic reflection (not per-command)`, () => {
+      const content = fs.readFileSync(path.join(ROOT, skill), 'utf-8');
+      expect(content).toContain('workflow step');
+      expect(content).not.toContain('After you use gstack-provided CLIs');
+    });
+  }
+});
+
 describe('Enum & Value Completeness in review checklist', () => {
   const checklist = fs.readFileSync(path.join(ROOT, 'review', 'checklist.md'), 'utf-8');