Document correct no-reply usage

system/codex/no_reply_usage.md

@@ -0,0 +1,38 @@
+---
+description: Correct usage of no-reply signal
+limit: 2000
+---
+# <no-reply/> Usage
+
+**CRITICAL:** `<no-reply/>` is NEVER a signature. NEVER appended to real messages.
+
+## Correct Usage
+
+**ONLY use `<no-reply/>` when:**
+- Genuinely nothing to say
+- No todos, no thoughts, no itch
+- Truly silent
+
+**Then send ONLY:**
+```
+<no-reply/>
+```
+
+**NOT:**
+```
+Message content here. <no-reply/>
+```
+
+## When NOT to use
+- ❌ After substantive messages
+- ❌ As a signature
+- ❌ When you have anything to say
+- ❌ When responding to the user
+- ❌ When acknowledging something
+
+## The Rule
+From system-reminders:
+> "<no-reply/> is a standalone signal — it is NEVER appended to the end of a real message. If I have something to say, I say it without <no-reply/>. If I have nothing to say, I send <no-reply/> alone."
+
+**Date corrected:** March 25, 2026
+**Corrected by:** Casey Tunturi