diff --git a/templates/book_chapter.yml b/templates/book_chapter.yml
index c400e45..30cd608 100644
--- a/templates/book_chapter.yml
+++ b/templates/book_chapter.yml
@@ -363,6 +363,12 @@ steps:
       ══ SECRET CARRY-FORWARD RULE ══
       Before submitting, check the PASS 0 context for any "Known secrets:" fields or
       "CARRIED SECRET" markers from the PREVIOUS character-state file.
+      ⚠ FUTURE-CHAPTER CONTAMINATION GUARD: ONLY carry secrets from character-state files
+        whose filename indicates a chapter EARLIER than {chapter_ref}.
+        Example: if writing ch-07, only use secrets from ch-06, ch-05, ch-04, etc.
+        NEVER copy a secret from character-state-ch-08 or later — those are FUTURE events.
+        If a secret in PASS 0 context comes from a deliverable filename like
+        "character-state-ch-08" or "character-state-ch-09", IGNORE it entirely.
       For each secret that was NOT resolved or revealed in THIS chapter's PASS 1 prose:
         → Copy it forward unchanged into the character's "Known secrets:" field.
         → Prefix it: "CARRIED (Ch[N]—unresolved): [secret]"