Shift-drag draws a line for belts and other transport pieces

Belts, filters, screw conveyors, shafts and pipe pieces never fill a rectangle;
a diagonal belt drag stays sloped with Shift held.

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

docs/DESIGN.md

@@ -477,6 +477,10 @@ above, including:
   chose to make stickiness grain against grain only: on anything built, every material slides
   freely, so slopes are useful for every material, while heaps keep their shape. Real chutes clog
   with sticky material and need cleaning, but that is micromanagement the game doesn't need.
+- **Belts and other transport pieces never fill a rectangle (2026-10-27).** The owner said Shift
+  doesn't need to fill a rectangle for belts, conveyors and the like. Belts, filters, screw
+  conveyors, shafts, pipes, pumps and outlets (`lineOnly()`) always draw a line, Shift or not, and
+  a diagonal belt drag stays sloped. Walls, grates and gates still Shift-fill.
 
 ## Ideas not built yet
 

docs/PROJECT_MAP.md

@@ -205,9 +205,9 @@ Material definitions: ids, properties and metal families. ids, and drill/tank ti
 Material tables: typed properties, casting groups, flags, parts and tool tiers. Typed property tables
 - variables: PH, DENS, KC, ICAP, CASTMETAL, METAL_TIER, SOLIDMETAL, F_NAT, F_CAST, F_BURN, P_NONE, P_SCREW_U, P_SCREW_D, P_SCREW_L, P_SCREW_R, P_GRATE, P_GOPEN, P_WHEEL, P_INTAKE, P_FILTER, P_PIPE, P_SCREW_UR, P_SCREW_DR, P_SCREW_DL, P_SCREW_UL, SCREW_PARTS, SCREW_DIRS, IS_SCREW, SCREW_DX, SCREW_DY, BIT_TIERS, TANK_TIERS, REACH
 
-### src/sim/pieces.js (177 lines)
+### src/sim/pieces.js (179 lines)
 Everything the player can build (PIECES): blocks, machines and molds, with costs and descriptions; filter settings; wall materials and their cost.
-- functions: isSlopeBelt, isFilter, isBelt, beltGrade, slopeShape, beltFaceY, filterVariant, beltDirection, isSlope, isWall, slopeCell, slopeCode, isPipeCode, filterable, cleanFilterCfg, filterRec, filterPassAt, filterInfo, sameFilter, wallCost
+- functions: isSlopeBelt, isFilter, isBelt, beltGrade, slopeShape, beltFaceY, filterVariant, beltDirection, isSlope, isWall, slopeCell, slopeCode, isPipeCode, lineOnly, filterable, cleanFilterCfg, filterRec, filterPassAt, filterInfo, sameFilter, wallCost
 - variables: BS, BP_WALL, BP_BELT, BP_SCREW, BP_SHAFT, BP_GRATE, BP_GATE, BP_FILTER, BP_PIPE, BP_PUMP, BP_OUTLET, BP_GRIND, BP_SAW, BP_PRESS, BP_RACK, BP_SLOPE_BL, BP_SLOPE_BR, BP_SLOPE_TL, BP_SLOPE_TR, BP_BELT_UP, BP_BELT_DOWN, BP_FILTER_UP, BP_FILTER_DOWN, filterCfg, WALL_OF, WALL_LIST, BAR_OF, GRAINS_PER_BAR, POWER_FREE, CASH, PIECES, PIECE_BY_ID, PIECE_BY_CODE, BELT_POWER, SCREW_POWER, FAN_POWER, WHEEL_K, ENGINE_K, MOLDS
 
 ### src/sim/economy.js (152 lines)
@@ -230,7 +230,7 @@ Exploration only: never changes grains or the random stream.
 - functions: fogAlloc, fogMark, fogSeen, fogInit, fogLook, fogRevealAround, fogRevealAll
 - variables: FOG, FOG_SENSE, FOG_SENSE_FADE, fog, FW, FH
 
-### src/sim/cells.js (223 lines)
+### src/sim/cells.js (225 lines)
 Cell helpers (setCell, move, enter) and the falling-sand movement of powders, liquids and gases (simMove).
 - functions: setCell, swapCells, move, enter, enterFree, powder, passable, liquid, gas, wakeBotPowder, simMove
 - variables: SORTP, SORTP_FUEL, LSTEP, LFILM, CORNER_SEAL
@@ -274,9 +274,9 @@ Cleats are rubber ribs standing up from a sloped belt's face, one every CLEAT_SP
 - functions: ribMove, cleatFoot, ribCells, slopeUphill, slopeFaceAt, pushRow, scoop, pocketRoom, advanceCleat, slopeRunKey, slopeCleatsTick, rebuildCleatMask, expelFromRib, screenNudge, wakeCleatLoad
 - variables: CLEAT_SPACING, CLEAT_HEIGHT, CLEAT_REACH, SCREEN_NUDGE_TICKS, cleatChunks, cleatMask, cleatCells, slopePhase, ribLog
 
-### src/sim/blocks.js (219 lines)
+### src/sim/blocks.js (235 lines)
 Building blocks: placing, integrity, removing, lines and rectangles of blocks.
-- functions: blockOf, blockCellList, pieceCost, setSlopeSeal, slopeSeal, slopeSealOwner, wallCells, canPlaceBlock, placeBlock, blockIntegrity, removeWallCell, removeBlock, diagonalDrag, blockLine, blockRect, blockInReach, blockIs, placeBlocks
+- functions: blockOf, blockCellList, pieceCost, setSlopeSeal, slopeSeal, slopeSealOwner, blockOwnsCell, clearStraySeals, wallCells, canPlaceBlock, placeBlock, blockIntegrity, removeWallCell, removeBlock, diagonalDrag, blockLine, blockRect, blockInReach, blockIs, placeBlocks
 
 ### src/sim/molds.js (317 lines)
 Molds: cavities for castings; ingot troughs empty themselves below. Removal returns set metal.
@@ -347,7 +347,7 @@ World generation helpers: noise and removal of tiny hard rock specks.
 World generation: staged terrain, ore, caves and placement, with synchronous and async entry points.
 - functions: generateWorld, generateWorldAsync
 
-### src/sim/save.js (179 lines)
+### src/sim/save.js (180 lines)
 Saving and loading a world (serializeWorld / deserializeWorld) and old-save migration.
 - functions: serializeWorld, deserializeWorld, startLoadWake, wakeLoadArea, wakeLoadNearBot, loadWakeTick
 - variables: SAVE_VERSION, TOFF
@@ -449,7 +449,7 @@ The build menu along the bottom: categories, piece tiles and their icons.
 - functions: pieceIcon, catOf, selectBuildCat, cycleBuildCat, buildVariantChips, renderBuildBar, setupBuildBar
 - variables: BUILD_CATS, BUILD_ORDER, PIECE_ICONS, lastBuildKey, lastBuildMenu
 
-### src/ui/selection.js (120 lines)
+### src/ui/selection.js (121 lines)
 Tool selection: cycling, drill tuning, piece variants and costs.
 - functions: pieceSize, pieceUsesWall, setDrillWidth, tuneUnderCursor, cycleItem, cycleWall, rotate, toggleBlow, pickFilterUnderCursor, toggleFilterMat, setBrush, pieceV, pieceExtra, filterBlockAt, chipCost, pieceCostNow, pieceCode, turnSlope
 

docs/agent-log.md

@@ -4,6 +4,17 @@ What agents have done, newest first. Add an entry for every piece of work: the d
 note or request it was for, what changed, the files touched, the tests run, and anything left
 open or not verified. Keep each entry short; the git history has the details.
 
+## 2026-10-27: Shift-drag draws a line for transport pieces (Claude Code)
+
+- Owner request: Shift shouldn't fill a rectangle for belts, conveyors and similar. New
+  `lineOnly(code)` in `src/sim/pieces.js` (belts, filters, screw conveyors, shafts, pipe pieces);
+  `primaryRelease` (`src/ui/actions.js`) and the drag preview (`src/ui/previews.js`) ignore Shift
+  for them, and `pieceCode` (`src/ui/selection.js`) no longer flattens a diagonal belt drag on
+  Shift. Build-menu "How to place" and the notebook say so; the notebook's stale "cleats up or
+  down" line now says uphill only.
+- Tests: play.py checks a Shift-drag with a belt lays a 3-piece sloped line. Full
+  `run_all --browser` passes.
+
 ## 2026-10-27: t61 sticky materials slide freely on built surfaces (Claude Code)
 
 - The owner's video showed clay lumps creeping down a sloped wall; removing a piece was