fix: address review findings on milestone-summary PR

1. Add <success_criteria> section to command (pattern compliance)
2. Fix archived audit path: check .planning/milestones/ not .planning/
3. Add RESEARCH.md to command context block
4. Add empty phase handling (graceful skip to minimal summary)
5. Add overwrite guard for existing summary files
6. Add 7 new tests: overwrite guard, empty phases, audit paths,
   success_criteria, RESEARCH.md context, artifact path resolution

Tests: 18/18 milestone-summary, 1184/1184 full suite

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

tests/milestone-summary.test.cjs

@@ -111,4 +111,82 @@ describe('milestone-summary workflow', () => {
       'should update STATE.md via gsd-tools'
     );
   });
+
+  test('workflow has overwrite guard for existing summaries', () => {
+    const content = fs.readFileSync(workflowPath, 'utf-8');
+    assert.ok(
+      content.includes('already exists'),
+      'should check for existing summary before overwriting'
+    );
+  });
+
+  test('workflow handles empty phase directories gracefully', () => {
+    const content = fs.readFileSync(workflowPath, 'utf-8');
+    assert.ok(
+      content.includes('no phase directories') || content.includes('No phases'),
+      'should handle case where no phases exist'
+    );
+  });
+
+  test('workflow checks both audit file locations for archived milestones', () => {
+    const content = fs.readFileSync(workflowPath, 'utf-8');
+    assert.ok(
+      content.includes('.planning/milestones/v${VERSION}-MILESTONE-AUDIT.md'),
+      'should check milestones/ directory for archived audit file'
+    );
+  });
+});
+
+describe('milestone-summary command structure', () => {
+  test('command has success_criteria section', () => {
+    const content = fs.readFileSync(commandPath, 'utf-8');
+    assert.ok(
+      content.includes('<success_criteria>'),
+      'should have success_criteria section (follows complete-milestone pattern)'
+    );
+  });
+
+  test('command context lists RESEARCH.md', () => {
+    const content = fs.readFileSync(commandPath, 'utf-8');
+    assert.ok(
+      content.includes('RESEARCH.md'),
+      'should list RESEARCH.md in context block'
+    );
+  });
+});
+
+describe('milestone-summary artifact path resolution', () => {
+  const { createTempProject, cleanup } = require('./helpers.cjs');
+  let tmpDir;
+
+  test('archived milestone paths point to milestones/ directory', () => {
+    const content = fs.readFileSync(workflowPath, 'utf-8');
+    // Archived roadmap path should be under milestones/
+    assert.ok(
+      content.includes('.planning/milestones/v${VERSION}-ROADMAP.md'),
+      'archived ROADMAP path should be under .planning/milestones/'
+    );
+    assert.ok(
+      content.includes('.planning/milestones/v${VERSION}-REQUIREMENTS.md'),
+      'archived REQUIREMENTS path should be under .planning/milestones/'
+    );
+    assert.ok(
+      content.includes('.planning/milestones/v${VERSION}-MILESTONE-AUDIT.md'),
+      'archived AUDIT path should be under .planning/milestones/'
+    );
+  });
+
+  test('current milestone paths point to .planning/ root', () => {
+    const content = fs.readFileSync(workflowPath, 'utf-8');
+    // Current milestone should read from .planning/ root
+    const lines = content.split('\n');
+    const currentSection = lines.slice(
+      lines.findIndex(l => l.includes('Current/in-progress')),
+      lines.findIndex(l => l.includes('Current/in-progress')) + 10
+    ).join('\n');
+    assert.ok(
+      currentSection.includes('ROADMAP_PATH=".planning/ROADMAP.md"'),
+      'current ROADMAP path should be at .planning/ root'
+    );
+  });
 });