"Doesn't connect" marks on transport ends that would join one block off (t67 phase 4)

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

src/render/overlays.js

@@ -53,6 +53,28 @@ function drawFlowArrows() {
   }
   ctx.restore();
 }
+// "Doesn't connect": a red ring with a slash at a transport end that would join one block up or
+// down (nearMiss), on built pieces, ghosts and the drag preview alike.
+function drawJoinMark(bx, by, end, code, v) {
+  const e = pieceEnds(code, v)[end], ctx = R.ctx, r = Math.max(3, BS * R.zp * 0.24);
+  const c = worldToScreenPx(bx * BS + BS / 2 + e.dx * BS / 2, by * BS + BS / 2 + e.dy * BS / 2);
+  ctx.save();
+  ctx.fillStyle = 'rgba(14,12,11,0.7)'; ctx.beginPath(); ctx.arc(c.x, c.y, r * 1.2, 0, Math.PI * 2); ctx.fill();
+  ctx.strokeStyle = '#ef6a55'; ctx.lineWidth = Math.max(1.2, r * 0.3);
+  ctx.beginPath(); ctx.arc(c.x, c.y, r * 0.75, 0, Math.PI * 2); ctx.stroke();
+  ctx.beginPath(); ctx.moveTo(c.x - r * 0.53, c.y + r * 0.53); ctx.lineTo(c.x + r * 0.53, c.y - r * 0.53); ctx.stroke();
+  ctx.restore();
+}
+function drawJoinMarks() {
+  const v = viewCells();
+  const bx0 = Math.max(0, Math.floor(R.camX / BS)), bx1 = Math.min(BW - 1, Math.floor((R.camX + v.w) / BS));
+  const by0 = Math.max(0, Math.floor(R.camY / BS)), by1 = Math.min(BH - 1, Math.floor((R.camY + v.h) / BS));
+  for (let by = by0; by <= by1; by++) for (let bx = bx0; bx <= bx1; bx++) {
+    const b = by * BW + bx, ghost = ghostBlocks.get(b), code = ghost ? ghost[0] : blockP[b], vv = ghost ? ghost[1] : blockV[b];
+    if (!code || !pieceEnds(code, vv).length) continue;
+    for (let end = 0; end < 2; end++) if (nearMiss(bx, by, end, ghostBlocks.size ? ghostBlocks : null)) drawJoinMark(bx, by, end, code, vv);
+  }
+}
 // Outline a run of blocks: strong while it is being edited, faint when pointed at
 function drawRunOutline(run, strong) {
   if (!run || !run.length) return;