diff --git a/tools/re-capture/screen_id.py b/tools/re-capture/screen_id.py
index 5a09dad3..8de3e198 100755
--- a/tools/re-capture/screen_id.py
+++ b/tools/re-capture/screen_id.py
@@ -35,7 +35,34 @@ import sys
 W, H = 320, 180
 
 
+def frame_size(path):
+    """(w, h) of the capture, or None if it cannot be read."""
+    out = subprocess.run(["identify", "-format", "%w %h", path],
+                         capture_output=True, text=True).stdout.split()
+    try:
+        return int(out[0]), int(out[1])
+    except (IndexError, ValueError):
+        return None
+
+
+# A capture that is not a plausible game frame must be REJECTED, not classified.
+# MEASURED 2026-08-26: a guard shot came back 10x710 -- a sliver -- and every
+# statistic below is an area fraction, so the sliver classified cleanly as
+# `menu`. The guard passed, the fixed key sequence was issued anyway, and the run
+# loaded a TUTORIAL instead of the save's Stage 02.
+#
+# This is the SECOND time this has been paid for. `bin/screenshot`'s own header
+# records the first (2026-08-18): a second window of class "xenia_canary" meant
+# grabs came back as slivers and "a whole session's screen ids were noise". That
+# fix hardened the CAPTURE side only, so the same failure still reaches the
+# oracles by any other path. Reject it here too, where the answer is consumed.
+MIN_W, MIN_H = 640, 360
+
+
 def features(path):
+    size = frame_size(path)
+    if size is None or size[0] < MIN_W or size[1] < MIN_H:
+        return None
     raw = subprocess.run(
         ["convert", path, "-alpha", "off", "-resize", f"{W}x{H}!", "-depth", "8",
          "rgb:-"], capture_output=True).stdout
@@ -57,7 +84,7 @@ def features(path):
 
 def classify(f):
     if f is None:
-        return "none"
+        return "none"      # unreadable OR not a plausible frame -- never a screen
     # Flight first: the HUD paints far more green than any menu.
     # (READY ROOM is checked before the menu rule because it is also dark-ish
     # and strongly blue, and would otherwise be swallowed by it.)