fix: use correct block name in messages template + add TPL-008 rule

- Fix messages.html: change {% block page_scripts %} to {% block extra_scripts %}
  (page_scripts doesn't exist in admin/base.html, causing JS not to load)

- Add TPL-008 architecture rule to catch invalid template block names
  This prevents silent failures where content in undefined blocks is ignored

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

.architecture-rules/frontend.yaml

@@ -243,6 +243,35 @@ template_rules:
       file_pattern: "app/templates/**/*.html"
       recommended_pattern: '<template x-if="items.length === 0">No items</template>'
 
+  - id: "TPL-008"
+    name: "Use valid block names from base templates"
+    severity: "error"
+    description: |
+      Templates must use block names that exist in their base template.
+      Using undefined blocks silently fails (content is not rendered).
+
+      Admin base blocks: title, extra_head, alpine_data, content, extra_scripts
+      Vendor base blocks: title, extra_head, alpine_data, content, extra_scripts
+      Shop base blocks: title, description, extra_head, alpine_data, content, extra_scripts
+
+      WRONG: {% block page_scripts %}...{% endblock %}  (undefined)
+      RIGHT: {% block extra_scripts %}...{% endblock %}
+    pattern:
+      file_pattern: "app/templates/admin/**/*.html"
+      valid_blocks:
+        - "title"
+        - "extra_head"
+        - "alpine_data"
+        - "content"
+        - "extra_scripts"
+      forbidden_patterns:
+        - "{% block page_scripts %}"
+        - "{% block scripts %}"
+        - "{% block js %}"
+        - "{% block footer_scripts %}"
+      exceptions:
+        - "base.html"
+
 # ============================================================================
 # FRONTEND COMPONENT RULES
 # ============================================================================

app/templates/admin/messages.html

@@ -331,6 +331,6 @@
 {% endcall %}
 {% endblock %}
 
-{% block page_scripts %}
+{% block extra_scripts %}
 <script src="{{ url_for('static', path='admin/js/messages.js') }}"></script>
 {% endblock %}

scripts/validate_architecture.py

@@ -812,6 +812,10 @@ class ArchitectureValidator:
             # TPL-007: Check empty state implementation
             self._check_template_empty_state(file_path, content, lines)
 
+            # TPL-008: Check for invalid block names
+            if is_admin:
+                self._check_valid_block_names(file_path, content, lines)
+
         if is_base_or_partial:
             return
 
@@ -1053,6 +1057,50 @@ class ArchitectureValidator:
                 suggestion='Add <template x-if="items.length === 0">No items found</template>',
             )
 
+    def _check_valid_block_names(
+        self, file_path: Path, content: str, lines: list[str]
+    ):
+        """TPL-008: Check that templates use valid block names from base template"""
+        if "noqa: tpl-008" in content.lower():
+            return
+
+        # Skip base templates
+        if file_path.name == "base.html":
+            return
+
+        # Valid admin template blocks
+        valid_blocks = {"title", "extra_head", "alpine_data", "content", "extra_scripts"}
+
+        # Common invalid block names that developers might mistakenly use
+        invalid_blocks = {
+            "page_scripts": "extra_scripts",
+            "scripts": "extra_scripts",
+            "js": "extra_scripts",
+            "footer_scripts": "extra_scripts",
+            "head": "extra_head",
+            "body": "content",
+            "main": "content",
+        }
+
+        import re
+        block_pattern = re.compile(r"{%\s*block\s+(\w+)\s*%}")
+
+        for i, line in enumerate(lines, 1):
+            match = block_pattern.search(line)
+            if match:
+                block_name = match.group(1)
+                if block_name in invalid_blocks:
+                    self._add_violation(
+                        rule_id="TPL-008",
+                        rule_name="Use valid block names from base templates",
+                        severity=Severity.ERROR,
+                        file_path=file_path,
+                        line_number=i,
+                        message=f"Invalid block name '{block_name}' - this block doesn't exist in admin/base.html",
+                        context=line.strip(),
+                        suggestion=f"Use '{{% block {invalid_blocks[block_name]} %}}' instead",
+                    )
+
     def _check_pagination_macro_usage(
         self, file_path: Path, content: str, lines: list[str]
     ):