diff --git a/AGENTS.md b/AGENTS.md
index 29ef02b..02424cb 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -131,6 +131,7 @@ This project has domain-specific skills available in `**/skills/**`. You MUST ac
 
 - Every change must be programmatically tested. Write a new test or update an existing test, then run the affected tests to make sure they pass.
 - Run the minimum number of tests needed to ensure code quality and speed. Use `php artisan test --compact` with a specific filename or filter.
+- **Environment Isolation during Test Runs (IMPORTANT)**: The test runner environment (e.g. `vendor/bin/pest` or `php artisan test`) can be polluted by the main project's local `.env` file settings if run directly in the active shell. This pollution can override test-specific configurations defined in `phpunit.xml` and lead to unexpected failures, such as CSRF (`419 Page Expired`) errors or database connection issues. Always prefix test commands with `env -i PATH=$PATH HOME=$HOME TERM=$TERM` (e.g., `env -i PATH=$PATH HOME=$HOME TERM=$TERM vendor/bin/pest`) to enforce a clean, isolated environment run.
 
 === inertia-laravel/core rules ===