docs: require Co-authored-by trailer in commit messages for AI agents

AGENTS.md

@@ -211,3 +211,17 @@ The repository includes preconfigured tasks in [`.vscode/tasks.json`](.vscode/ta
 5. **Code Style:**
    - Follow the naming and check options specified in [`.clang-tidy`](.clang-tidy) (functions/variables in `snake_case`, classes/structs in `CamelCase`).
    - Run `cmake --build build` to verify clean compilation without warnings or errors.
+6. **Commit Message Attribution:**
+   - Every commit message generated by an AI agent **must** include a `Co-authored-by` trailer, separated from the subject/body by a blank line. Each agent should substitute its own name and contact address:
+     ```
+     Co-authored-by: <Agent Name> <agent-email-or-url>
+     ```
+   - Example commit message format:
+     ```
+     feat: add cursed apple spawn rate tuning
+
+     Expose CURSE_SPAWN_CHANCE constant in consts.h so it can be adjusted
+     without touching game logic.
+
+     Co-authored-by: <Agent Name> <agent-email-or-url>
+     ```