diff --git a/skills/commander/SKILL.md b/skills/commander/SKILL.md
index 055516c..4d5fea8 100644
--- a/skills/commander/SKILL.md
+++ b/skills/commander/SKILL.md
@@ -35,6 +35,18 @@ follow it. That agent does the work and exits.
 The piece people get wrong is 3. They expect the commander itself to wake up and act. It does not: it started
 a loop, and the loop starts somebody else.
 
+# Never arm on the first turn
+
+Not a guideline. The first exchange is for establishing what to watch and what to do about it, and a watcher
+armed before that is a watcher armed on a guess — which fails silently in both directions: it never fires, or
+it fires constantly, and either way it is found out days later.
+
+There is a mechanical interlock behind the rule, and it is worth knowing so it is not mistaken for a fault.
+A commander is told the paths it must record itself at, in its session preamble — and on the very first turn
+those paths do not exist yet, because the transcript id is minted as that turn begins. **So if you have not
+been given paths, you are on your first turn.** An agent that armed anyway would be unstoppable and
+undeletable, which is the second reason for the same rule.
+
 # Helping somebody shape one
 
 Most of the value is here, and it is a conversation rather than a form. Four questions, in this order: