docs+test: SKILL authoring guidance + regression tests

Adds "Writing SKILL templates" section to CLAUDE.md explaining that
templates are prompts, not scripts. Adds validation test catching
hardcoded 'main' in git commands, and resolver content test.

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

CLAUDE.md

@@ -64,6 +64,23 @@ SKILL.md files are **generated** from `.tmpl` templates. To update docs:
 To add a new browse command: add it to `browse/src/commands.ts` and rebuild.
 To add a snapshot flag: add it to `SNAPSHOT_FLAGS` in `browse/src/snapshot.ts` and rebuild.
 
+## Writing SKILL templates
+
+SKILL.md.tmpl files are **prompt templates read by Claude**, not bash scripts.
+Each bash code block runs in a separate shell — variables do not persist between blocks.
+
+Rules:
+- **Use natural language for logic and state.** Don't use shell variables to pass
+  state between code blocks. Instead, tell Claude what to remember and reference
+  it in prose (e.g., "the base branch detected in Step 0").
+- **Don't hardcode branch names.** Detect `main`/`master`/etc dynamically via
+  `gh pr view` or `gh repo view`. Use `{{BASE_BRANCH_DETECT}}` for PR-targeting
+  skills. Use "the base branch" in prose, `<base>` in code block placeholders.
+- **Keep bash blocks self-contained.** Each code block should work independently.
+  If a block needs context from a previous step, restate it in the prose above.
+- **Express conditionals as English.** Instead of nested `if/elif/else` in bash,
+  write numbered decision steps: "1. If X, do Y. 2. Otherwise, do Z."
+
 ## Browser interaction
 
 When you need to interact with a browser (QA, dogfooding, cookie setup), use the

test/gen-skill-docs.test.ts

@@ -131,6 +131,27 @@ describe('gen-skill-docs', () => {
   });
 });
 
+describe('BASE_BRANCH_DETECT resolver', () => {
+  // Find a generated SKILL.md that uses the placeholder (ship is guaranteed to)
+  const shipContent = fs.readFileSync(path.join(ROOT, 'ship', 'SKILL.md'), 'utf-8');
+
+  test('resolver output contains PR base detection command', () => {
+    expect(shipContent).toContain('gh pr view --json baseRefName');
+  });
+
+  test('resolver output contains repo default branch detection command', () => {
+    expect(shipContent).toContain('gh repo view --json defaultBranchRef');
+  });
+
+  test('resolver output contains fallback to main', () => {
+    expect(shipContent).toMatch(/fall\s*back\s+to\s+`main`/i);
+  });
+
+  test('resolver output uses "the base branch" phrasing', () => {
+    expect(shipContent).toContain('the base branch');
+  });
+});
+
 /**
  * Quality evals — catch description regressions.
  *

test/skill-validation.test.ts

@@ -361,6 +361,64 @@ describe('Greptile history format consistency', () => {
   });
 });
 
+// --- Hardcoded branch name detection in templates ---
+
+describe('No hardcoded branch names in SKILL templates', () => {
+  const tmplFiles = [
+    'ship/SKILL.md.tmpl',
+    'review/SKILL.md.tmpl',
+    'qa/SKILL.md.tmpl',
+    'plan-ceo-review/SKILL.md.tmpl',
+    'retro/SKILL.md.tmpl',
+  ];
+
+  // Patterns that indicate hardcoded 'main' in git commands
+  const gitMainPatterns = [
+    /\bgit\s+diff\s+(?:origin\/)?main\b/,
+    /\bgit\s+log\s+(?:origin\/)?main\b/,
+    /\bgit\s+fetch\s+origin\s+main\b/,
+    /\bgit\s+merge\s+origin\/main\b/,
+    /\borigin\/main\b/,
+  ];
+
+  // Lines that are allowed to mention 'main' (fallback logic, prose)
+  const allowlist = [
+    /fall\s*back\s+to\s+`main`/i,
+    /fall\s*back\s+to\s+`?main`?/i,
+    /typically\s+`?main`?/i,
+    /If\s+on\s+`main`/i,  // old pattern — should not exist
+  ];
+
+  for (const tmplFile of tmplFiles) {
+    test(`${tmplFile} has no hardcoded 'main' in git commands`, () => {
+      const filePath = path.join(ROOT, tmplFile);
+      if (!fs.existsSync(filePath)) return;
+      const lines = fs.readFileSync(filePath, 'utf-8').split('\n');
+      const violations: string[] = [];
+
+      for (let i = 0; i < lines.length; i++) {
+        const line = lines[i];
+        const isAllowlisted = allowlist.some(p => p.test(line));
+        if (isAllowlisted) continue;
+
+        for (const pattern of gitMainPatterns) {
+          if (pattern.test(line)) {
+            violations.push(`Line ${i + 1}: ${line.trim()}`);
+            break;
+          }
+        }
+      }
+
+      if (violations.length > 0) {
+        throw new Error(
+          `${tmplFile} has hardcoded 'main' in git commands:\n` +
+          violations.map(v => `  ${v}`).join('\n')
+        );
+      }
+    });
+  }
+});
+
 // --- Part 7b: TODOS-format.md reference consistency ---
 
 describe('TODOS-format.md reference consistency', () => {