Rename screw tubes to screw conveyors (t44)

Player text says Screw conveyor; code uses screw (BP_SCREW, piece id
screw, screwIntake...). No compatibility code for old saves or
blueprints. Suite outputs match before and after apart from names.

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

docs/DESIGN.md

@@ -49,7 +49,7 @@ decides something new, add it under "Decisions" with the date.
 4. Bars drop out of the bottom of the mold; collect them and sell them at the trade dock, or fill buyers' orders, which pay more.
 5. Better bits (copper, then iron, then steel) open harder rock: granite, then basalt. Deeper
    ores give tin, zinc, silver and gold, and alloys (bronze, brass) pay more.
-6. Automate with belts, screw tubes, filters, fans, pipes and machines. Pay off the claim.
+6. Automate with belts, screw conveyors, filters, fans, pipes and machines. Pay off the claim.
 
 ## Systems in brief
 
@@ -74,7 +74,7 @@ Details and numbers live in the code and in `docs/systems/`.
 - **Drill:** see `docs/systems/dig-tools.md`. Pulse widths, tuning to one material, hardness by
   bit tier.
 - **Building:** a 4×4-grain block grid.
-  - Blocks: walls of any of several materials, belts, screw tubes, filters, grates, gates,
+  - Blocks: walls of any of several materials, belts, screw conveyors, filters, grates, gates,
     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;
@@ -140,7 +140,7 @@ above, including:
 - **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. 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,
+- **Screw conveyors 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,
   the load above it stands still and the belt slips underneath; the top no longer slides over
@@ -177,7 +177,7 @@ above, including:
   popup. The owner asked for a general description rather than the selected building.
 - **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.
 
-- **Fewer, smaller messages.** Molds show only a small percentage, red when blocked or spoiled and gold when a casting waits for F; details are in the hover panel. Bars dropping, blocked molds and set castings no longer pop up cards or toasts. Fan heat is a red marker on the fan; melted tubes and machines get a short red label where they were. Status lines are one short sentence. The owner found the messages too large and too many.
+- **Fewer, smaller messages.** Molds show only a small percentage, red when blocked or spoiled and gold when a casting waits for F; details are in the hover panel. Bars dropping, blocked molds and set castings no longer pop up cards or toasts. Fan heat is a red marker on the fan; melted screw conveyors and machines get a short red label where they were. Status lines are one short sentence. The owner found the messages too large and too many.
 
 - **World sounds are local.** Sounds from the world (water sizzling on hot metal or lava, and
   any other event with a place) are heard around the bot, whatever the zoom: full volume within
@@ -190,14 +190,14 @@ above, including:
 - **The silo has pixel art in the pixel look**, drawn grain by grain like the rest of the world;
   the smooth look keeps the illustrated silo. The owner noticed it looked the same in both.
 
-- **Screw tubes use all their lanes.** Grains in an up or down tube shift sideways toward the
+- **Screw conveyors use all their lanes.** Grains in an up or down screw conveyor shift sideways toward the
   emptier lanes of the block, and grains taken in from the side go to the far lanes first. A
   block-wide lift fed by a belt from the side now carries about 90% of what the belt brings
   (before, only the edge lane filled: the owner saw one line on either side). Belts keep their
   speed.
-- **Screw tubes carry bars**, one whole bar at a time, in line with the grains: a belt pushes a
-  bar into a tube's side, it rides through corners and leaves the mouth. The owner asked how bars
-  should be moved and chose tubes over a separate bar lift.
+- **Screw conveyors carry bars**, one whole bar at a time, in line with the grains: a belt pushes a
+  bar into a screw conveyor's side, it rides through corners and leaves the mouth. The owner asked how bars
+  should be moved and chose screw conveyors over a separate bar lift.
 - **Several worlds are kept.** Each world has its own save and autosave; the title screen's Worlds
   list loads, renames and deletes them, and a new or imported world never overwrites another. An
   old single save becomes 'World 1'. The owner asked for multiple saves.
@@ -214,7 +214,7 @@ above, including:
   and the surface start seen. The owner chose line of sight over a plain circle around the bot.
 - **Bars pile neatly, and a Bar rack stores them (t1).** Bars that come to rest snap to a tidy
   brick pattern so piles have no air gaps; a Bar rack machine (the Silo for bars) takes them from
-  a belt or tube, counts them and lets them out with F. The owner wanted bar storage that doesn't
+  a belt or screw conveyor, counts them and lets them out with F. The owner wanted bar storage that doesn't
   waste space, like stacked ingots in real life.
   As built: a resting bar snaps to a 2-grain grid, and one with fewer than 2 of its 4 bottom cells
   supported tips into the gap beside it. Storage became Rack blocks rather than a machine, like
@@ -372,25 +372,25 @@ above, including:
   also fills one cell past its corner so a diagonal run is sealed (grains move diagonally and
   would otherwise slip through where two pieces meet). Square walls placed diagonally still
   touch only at corners and leak there, like any square blocks.
-  Later the same day the owner asked for the Wall piece itself to work diagonally, the way tubes
+  Later the same day the owner asked for the Wall piece itself to work diagonally, the way screw conveyors
   do, so the separate Sloped wall piece left the build menu: a wall drag at about 45° lays slopes
   (solid side below, T flips it during the drag), straight drags and clicks lay squares, and for a
   single block T cycles square and the four corners. Slope ids are unchanged, so saves still load.
 
-- **Diagonal screw tubes (t35, 2026-10-25).** Tubes run in eight directions. A drag at about 45°
-  lays a diagonal run pointing along the drag, and R cycles all eight for a single tube. Diagonal
-  runs carry grains at the same rate as straight ones, join straight tubes and belts, and carry
+- **Diagonal screw conveyors (t35, 2026-10-25).** Screw conveyors run in eight directions. A drag at about 45°
+  lays a diagonal run pointing along the drag, and R cycles all eight for a single screw conveyor. Diagonal
+  runs carry grains at the same rate as straight ones, join straight screw conveyors and belts, and carry
   bars level, a block every eight ticks. They use new part ids (11-14) because part ids are saved.
 
 - **Sloped belts and filters (t40, 2026-10-25).** The owner asked for belts, then filters, to work
-  diagonally like tubes and walls. A Belt or Filter drag at about 45° lays slope-shaped blocks
+  diagonally like screw conveyors and walls. A Belt or Filter drag at about 45° lays slope-shaped blocks
   whose face is a running belt, carrying grains and bars up or down in the drag's direction at
   flat-belt speed; the face grips its load, so nothing slides back. A sloped filter drops what it
   passes out underneath and carries the rest. New block codes (19-22), so saves still load.
 - **Square corners hold grains (t39, 2026-10-26).** The owner wants square wall staircases to
   hold material instead of leaking through each touching corner. Powder, liquid and gas cannot
   step diagonally between two solid neighbours; powder neighbours still allow free piles to
-  slide as before. Free flyers and diagonal screw intakes obey the same solid-corner boundary.
+  slide as before. Free flyers and diagonal screw conveyor intakes obey the same solid-corner boundary.
   Screw lane transport is unchanged. World generation disables cell corner sealing while
   settling loose ground, preserving existing seed layouts. This supersedes the square-wall
   leakage described in the t36 decision below.
@@ -400,6 +400,9 @@ above, including:
 - **Distant drill aim is normal (t41, 2026-10-26).** The owner normally points beyond the
   drill's reach and expects players to do the same. Keep the pulse colour and light crosshair,
   mark the pulse's far edge, and omit distance warnings for the drill. Other tools still warn.
+- **Screw conveyors (t44, 2026-10-26).** The owner chose the real machine name for screw
+  conveyors; code uses `screw` because `conveyor` also covers belts and filters. Transport,
+  numeric ids and save versions stay unchanged.
 - **No backward compatibility for now (2026-10-26).** The owner will start a new world after
   changes: no one is playing the game for real yet. Changes may break old saves and blueprints;
   don't add migration or alias code for them (first used by the t44 rename to screw conveyors).