docs: add 'test with user command, not substitute' rule

projects/AGENTS.md

@@ -22,6 +22,10 @@ When delegating work to subagents, follow this iteration loop:
    - `check-parens` reports zero issues on modified org files
    - If the project has a runnable entry point (daemon, TUI, demo), verify it
      starts and the change is visible
+   - **Test with the user's command, not a substitute.** If the user runs
+     `passepartout tui`, test with `passepartout tui`. Loading a stale fasl
+     or bypassing the normal entry point will miss compilation errors that
+     only appear on a fresh build.
 
 Key principles:
 - The subagent implements, the architect reviews. Do not switch roles.