Ingot molds empty themselves (no F); removing a mold returns its set metal

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/DESIGN.md

@@ -78,9 +78,10 @@ Details and numbers live in the code and in `docs/systems/`.
     pipes, pumps, outlets.
   - Machines: fan, Refiner, Stone cutter, Silo.
   - Molds: ingot, bit, tank. Ingot bars drop out of the bottom onto whatever is under the mold;
-    leave one open block below and a belt under that carries them off. F is optional upkeep: it
-    cleans the trough, chips off slag and rakes the furnace grate. Short stubs stay for the next
-    firing.
+    leave one open block below and a belt under that carries them off. Ingot molds empty themselves:
+    junk and mixed scrap drop below, slag is thrown away and the grate above is raked. Short stubs
+    stay for the next firing. Removing any mold returns its set metal to the bag: whole bars as
+    bars, the rest as scrap.
   - Build actions: drag for lines, Shift-drag for rectangles, hold G to replace, hold C / X and
     drag to copy / cut, V to paste, Ctrl+Z to undo, middle mouse to pick,
     Shift+Q/E to switch build tabs.
@@ -137,7 +138,7 @@ above, including:
 **2026-10-23:**
 - **Ingot molds drop bars below automatically.** The owner reported bars being thrown into the
   furnace above and wants belts underneath to carry them off. Blocked bars wait in the trough;
-  short stubs stay for the next firing. F stays available for cleaning and raking.
+  short stubs stay for the next firing. The mold cleans itself and rakes the grate after dropping bars or clearing junk.
 - **Screw tubes carry no more than belts:** they move every other tick. For more throughput,
   build more lines.
 - **A heap on a belt moves as one**, up to 96 grains deep, not just its bottom layer. If a grain is blocked,
@@ -172,6 +173,8 @@ above, including:
 - **The build tool has a compact top-left card** like the other tools. The owner asked for it
   back after it was hidden; the long description stays in the hover popup.
 
+- **Ingot molds need no F.** They push junk and mixed metal out of the bottom as loose grains with the bars, throw slag away and rake the grate. Removing any mold returns its set metal: whole bars as bars, the rest as scrap. The owner asked what F was for once bars dropped on their own, and chose this over keeping F for cleaning.
+
 ## Ideas not built yet
 
 - **Concrete**, as a stronger wall material from rubble.