reject character/world updates that are <70% of original size

Adds _validate_update_size() safeguard that skips writing if the
LLM returns a fragment instead of the full file — warns on stderr.

tools/engine.py

@@ -636,8 +636,6 @@ class GameEngine:
             if finalize_call:
                 args = finalize_call.get("args", {})
                 errs = []
-                if not args.get("dm_status"):
-                    errs.append("dm_status is required")
                 if not args.get("book_log"):
                     errs.append("book_log is required")
                 if not args.get("user_prompt"):
@@ -767,13 +765,36 @@ class GameEngine:
 
     # ── State Persistence ───────────────────────────────────────────────
 
+    def _validate_update_size(self, name: str, new_content: str, path: Path) -> bool:
+        """Reject updates that are more than 30% shorter than the existing file
+        — likely the LLM pasted a fragment instead of the full state."""
+        if not path.exists():
+            return True
+        old = path.read_text().strip()
+        if not old:
+            return True
+        ratio = len(new_content) / len(old)
+        if ratio < 0.7:
+            import sys
+            print(
+                f"WARNING: {name} update rejected ({ratio:.0%} of original size "
+                f"= {len(new_content)} vs {len(old)} chars) — likely a partial paste.",
+                file=sys.stderr,
+            )
+            return False
+        return True
+
     def apply_state(self, result: TurnResult) -> None:
         """Write state changes from a TurnResult to disk."""
 
-        if result.character_updates:
+        if result.character_updates and self._validate_update_size(
+            "character", result.character_updates, CHAR_PATH
+        ):
             CHAR_PATH.write_text(result.character_updates.strip() + "\n")
 
-        if result.world_updates:
+        if result.world_updates and self._validate_update_size(
+            "world", result.world_updates, WORLD_PATH
+        ):
             WORLD_PATH.write_text(result.world_updates.strip() + "\n")
 
         if result.ambience: