test(email): add structural guard for shared email partials

docs/superpowers/plans/2026-06-26-email-templates-brand-hygiene.md

@@ -341,7 +341,7 @@ Cheap catch for future drift, and the **gate** for Tasks 6–9. No test framewor
 **Interfaces:**
 - Produces: a script that exits non-zero if any `email/*.html` (excluding `partials/`) is missing a header IMPORT, footer IMPORT, or `<!-- preheader -->` marker. Run after every template conversion.
 
-- [ ] **Step 1: Write the script**
+- [x] **Step 1: Write the script**
 
 ```js
 #!/usr/bin/env node
@@ -372,12 +372,12 @@ if (failures.length) {
 console.log(`Email template check passed (${files.length} templates).`);
 ```
 
-- [ ] **Step 2: Run it — expect failures for every not-yet-converted template, pass for `reset.html`**
+- [x] **Step 2: Run it — expect failures for every not-yet-converted template, pass for `reset.html`**
 
 Run: `node scripts/check-emails.js`
 Expected: FAIL, listing `welcome.html`, `verify-email.html`, `reset_notify.html`, `registration_accepted.html`, `invitation.html`, `banned.html`, `test.html`, `notification.html`, `digest.html` (reset.html absent from the list). This proves the guard discriminates.
 
-- [ ] **Step 3: Commit**
+- [x] **Step 3: Commit**
 
 ```bash
 git add scripts/check-emails.js

email/README.md

@@ -60,6 +60,9 @@ them to users on various events (password reset, digest, ban, etc.).
   comments. Keep that structure — don't refactor into modern CSS.
 - Don't hardcode user-facing copy; add/replace `[[email:…]]` keys and define
   them in the language files.
+- Run `node scripts/check-emails.js` after converting templates. It enforces
+  the shared-partial structure by requiring a header import, footer import,
+  and `<!-- preheader -->` marker in each `email/*.html` file.
 - Rebuild (`./nodebb build`) and use the ACP test-email button to verify.
 
 ## References

scripts/check-emails.js

@@ -0,0 +1,27 @@
+#!/usr/bin/env node
+// ponytail: 30-line structural guard, not a render test. Catches drift, not pixels.
+const fs = require('fs');
+const path = require('path');
+
+const dir = path.join(__dirname, '..', 'email');
+const files = fs.readdirSync(dir).filter((f) => f.endsWith('.html'));
+
+const failures = [];
+for (const f of files) {
+  const src = fs.readFileSync(path.join(dir, f), 'utf8');
+  const checks = [
+    [/IMPORT emails\/partials\/header\.(html|tpl)/, 'missing header IMPORT'],
+    [/IMPORT emails\/partials\/footer\.(html|tpl)/, 'missing footer IMPORT'],
+    [/<!-- preheader -->/, 'missing preheader marker'],
+  ];
+  for (const [re, msg] of checks) {
+    if (!re.test(src)) failures.push(`${f}: ${msg}`);
+  }
+}
+
+if (failures.length) {
+  console.error('Email template check FAILED:\n' + failures.join('\n'));
+  process.exit(1);
+}
+
+console.log(`Email template check passed (${files.length} templates).`);