diff --git a/AGENTS.md b/AGENTS.md
index 73e2226..3a4a6c0 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -23,3 +23,9 @@ Before responding to the first user message in a session, you MUST:
 Skipping this protocol caused real bugs and rework in past sessions
 (work landed on master, TDD order was lost, formatter not run, banned
 constructs slipped in). Treat the protocol as non-negotiable.
+
+## Command execution
+
+When running commands that need the Nix devshell, set `login: false`.
+The login shell resets `PATH` and can hide tools like `phpcs`, Cypress,
+and the devshell Node version.