Sloped walls with a flat 45° face, and diagonal wall lines (t36)

- New Sloped wall piece: a half-block triangle in any wall material, at half a wall's cost.
  Dragging walls or slopes at about 45° lays a diagonal line; the drag picks the slope's
  orientation and T flips or turns it.
- Each slope fills one cell past its corner, so a diagonal run is sealed against grains and water.
- New test/t_slopes.js: a slope funnel passes 400/400 sand (square steps 379/400).

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

test/play.py

@@ -676,6 +676,25 @@ with sync_playwright() as p:
     check('bot can sit inside a built wall', not ev(f'botOverlapSolid({wx_ - 2}, {wy_ - 2})'))
     check('bot cannot sit inside natural rock', ev(f'botOverlapSolid({bx}, {gy + 12})'))
 
+    # Slopes use the same mouse drag path as walls, with T for their corner.
+    pg.click('[data-piece="slope"]'); settle(60)
+    check('Sloped wall is next to Wall in the build menu', ev("piece().id === 'slope' && BUILD_CATS[0][1].slice(0,2).join(',') === 'wall,slope'"))
+    ev('GAME.wallMat = RSTONE; GAME.pieceDir.slope = 0')
+    drag(lambda: blk(bbx - 5, bby - 12), lambda: blk(bbx - 2, bby - 9))
+    check('diagonal slope drag places four oriented blocks', ev(f'Array.from({{length:4}}, (_,k)=>blockP[({bby}-12+k)*BW+{bbx}-5+k]).every(c=>c===BP_SLOPE_BL)'))
+    pg.keyboard.press('Control+z'); settle(60)
+    pg.keyboard.press('t'); settle(60)
+    check('T cycles the single slope corner', ev('GAME.pieceDir.slope === 1'))
+    pg.mouse.move(*blk(bbx - 5, bby - 12)); settle(60); pg.mouse.down()
+    pg.mouse.move(*blk(bbx - 2, bby - 9)); settle(60)
+    pg.keyboard.press('t'); settle(60); pg.mouse.up(); settle(60)
+    check('T flips a diagonal slope above its face', ev(f'Array.from({{length:4}}, (_,k)=>blockP[({bby}-12+k)*BW+{bbx}-5+k]).every(c=>c===BP_SLOPE_TR)'))
+    pg.keyboard.press('Control+z'); settle(60)
+    pg.click('[data-piece="wall"]'); settle(60)
+    drag(lambda: blk(bbx - 5, bby - 12), lambda: blk(bbx - 2, bby - 9))
+    check('square wall drag can also place a diagonal', ev(f'Array.from({{length:4}}, (_,k)=>blockP[({bby}-12+k)*BW+{bbx}-5+k]).every(c=>c===BP_WALL)'))
+    pg.keyboard.press('Control+z'); settle(60)
+
     # 6. ingot mold: click to place, pour, bars drop below, vacuum them
     ok = select('3', "piece().id === 'ingotmold'")
     check('E cycles to the ingot mold', ok)