diff --git a/docs/DESIGN.md b/docs/DESIGN.md
index d331fe8..b8d8bb1 100644
--- a/docs/DESIGN.md
+++ b/docs/DESIGN.md
@@ -511,6 +511,12 @@ above, including:
   edge-of-screen arrow, the first-start card names both and suggests starting left, signposts
   stand on indestructible plinths at spawn, and each warehouse is a landmark (crane or silo,
   beacon at night) with its road running a little way inland.
+- **Screws melting under hot loads stays, but must read clearly (t69, t70, 2026-10-27).** Hot
+  material still damages screw conveyors (above 1000°), but the owner wants the damage obvious
+  (a scorched or broken look, hover text, a first-time message), cheap to repair (build over it),
+  and warned about before it happens (a glow near the limit). A heat-resistant screw comes later
+  as an upgrade. Prompted by a long vertical screw that seemed to leak for no reason while it
+  carried hot rubble.
 
 ## Ideas not built yet