diff --git a/AGENTS.md b/AGENTS.md
index 02b1c4cb7..1557a7f56 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -137,7 +137,7 @@ const table = sqliteTable("session", {
 
 ## Testing
 
-- Avoid mocks as much as possible
+- Avoid mocks as much as possible, you shouldn't be using globalThis.\* at all unless it's the only option.
 - Test actual implementation, do not duplicate logic into tests
 - Tests cannot run from repo root (guard: `do-not-run-tests-from-root`); run from package dirs like `packages/opencode`.