refactor: apply review comments

CODE_GUIDELINES.md

@@ -1656,7 +1656,7 @@ end
 
 **Performance Tests:**
 
-Performance tests that explicitly validate performance characteristics should be tagged with `@tag :slow` or `@moduletag :slow` to exclude them from standard test runs. This improves developer feedback loops while maintaining comprehensive coverage.
+Performance tests that explicitly validate performance characteristics should be tagged with `@tag :slow` or `@describetag :slow` to exclude them from standard test runs. This improves developer feedback loops while maintaining comprehensive coverage.
 
 **When to Tag as `:slow`:**
 
@@ -1664,6 +1664,12 @@ Performance tests that explicitly validate performance characteristics should be
 - Tests that use large datasets (e.g., 50+ records) to test scalability
 - Tests that validate query optimization (N+1 prevention, index usage)
 
+**Tagging Guidelines:**
+
+- Use `@tag :slow` for individual tests
+- Use `@describetag :slow` for entire describe blocks (not `@moduletag`, as it affects all tests in the module)
+- Performance tests should include measurable assertions (query counts, timing with tolerance, etc.)
+
 **Running Tests:**
 
 ```bash
@@ -1673,7 +1679,7 @@ mix test --exclude slow
 # Performance tests only
 mix test --only slow
 
-# All tests
+# All tests (including slow tests)
 mix test
 ```
 ---