diff --git a/15-security-scanning.md b/15-security-scanning.md
index b40b9c1..6557d27 100644
--- a/15-security-scanning.md
+++ b/15-security-scanning.md
@@ -438,6 +438,15 @@ runs on every push and blocks the merge.
 
 ---
 
+### Gate 0: your hosted forge
+
+Most hosted forges run their own secret scanner on every push and reject the push if it finds a
+recognized key pattern (GitHub calls this *push protection*; GitLab and others have equivalents).
+That happens **before** any CI you wrote runs, so it is effectively *Gate 0* in this module. The
+planted `SYNC_API_KEY` in `lab/config.py` uses a generic high-entropy value (not an issuer
+pattern) so the lab can ship; in your real repo, treat your forge's push protection as the
+earliest gate and never paper over a bypass.
+
 ## Where it breaks
 
 The honest limits (these gates are necessary, not sufficient):