diff --git a/tests/unit/AGENTS.md b/tests/unit/AGENTS.md
index 80a3a87f959..9ce6c58cff7 100644
--- a/tests/unit/AGENTS.md
+++ b/tests/unit/AGENTS.md
@@ -1,6 +1,9 @@
 # tests/unit
 
-In-process. No network, clock or subprocess
+In-process. No network or subprocess
+
+Unit tests must not depend on the current time or execution speed. Use fixed timestamps for fixtures
+and controlled clocks for time-dependent behavior. Incidental clock reads inside production code are allowed
 
 ## What good looks like