update AGENTS.md

Author: whummer

aws-proxy/AGENTS.md

@@ -15,6 +15,7 @@ You are an AI agent tasked with adding additional functionality or test coverage
 * You can call different `make` targets (e.g., `make test`) in this repo (no need to prompt for confirmation)
 * For each new file created or existing file modified, add a header comment to the file, something like `# Note/disclosure: This file has been (partially or fully) generated by an AI agent.`
 * The proxy tests are executed against real AWS and may incur some costs, so rather than executing the entire test suite or entire modules, focus the testing on individual test functions within a module only.
+* Before claiming success, always double-check against real AWS (via `aws` CLI commands) that everything has been cleaned up and there are no leftover resources from the proxy tests.
 * Never add any `print(..)` statements to the code - use a logger to report any status to the user, if required.
 * To format/lint the codebase you can run `make format` and `make lint`.