Spur label: compute optimal position from trapezoid geometry

Position text at 55% height (toward wider area), then center
horizontally based on the actual right edge at the text's top,
minimizing overflow past the angled edge.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

svelte-app/src/lib/canvas/renderer.ts

@@ -556,12 +556,21 @@ function drawConveyanceLabel(ctx: CanvasRenderingContext2D, sym: PlacedSymbol) {
   let cx: number, cy: number, availW: number, availH: number;
   if (isSpurType(sym.symbolId)) {
     const w2 = sym.w2 ?? sym.w;
-    // The 90° corners are at x=0 (left edge). The rectangular region
+    // Find optimal position: push text down where trapezoid is widest,
-    // from x=0 to x=min(w2,w) always fits inside the trapezoid.
+    // then center horizontally in the available width at that height.
-    const safeW = Math.min(w2, sym.w);
+    // Trapezoid right edge at height y: w2 + (y/h) * (w - w2)
-    cx = sym.x + safeW / 2;
+    const fontSize = 14;
-    cy = sym.y + sym.h / 2;
+    const lineCount = lines.length;
-    availW = Infinity; // never shrink font for spurs — enough visual room
+    const th = fontSize * lineCount;
+    // Optimal cy: as low as possible (widest area), clamped to fit
+    const optCy = Math.min(sym.h - th / 2 - 1, sym.h * 0.55);
+    // Right edge at the TOP of the text block (most constraining)
+    const textTop = optCy - th / 2;
+    const rightEdgeAtTop = w2 + (Math.max(0, textTop) / sym.h) * (sym.w - w2);
+    // Center text in the available width (0 to rightEdgeAtTop)
+    cx = sym.x + rightEdgeAtTop / 2;
+    cy = sym.y + optCy;
+    availW = Infinity; // never shrink — position handles fit
     availH = sym.h;
   } else {
     cx = sym.x + sym.w / 2;

svelte-app/src/lib/export.ts

@@ -44,9 +44,13 @@ function emitConveyanceLabelInner(lines: string[], sym: PlacedSymbol) {
     textRotDeg = (textRotRad * 180) / Math.PI;
   } else if (isSpurType(sym.symbolId)) {
     const w2 = sym.w2 ?? sym.w;
-    const safeW = Math.min(w2, sym.w);
+    const fontSize = 14;
-    labelCx = sym.x + safeW / 2;
+    const th = fontSize * textLines.length;
-    labelCy = sym.y + sym.h / 2;
+    const optCy = Math.min(sym.h - th / 2 - 1, sym.h * 0.55);
+    const textTop = optCy - th / 2;
+    const rightEdgeAtTop = w2 + (Math.max(0, textTop) / sym.h) * (sym.w - w2);
+    labelCx = sym.x + rightEdgeAtTop / 2;
+    labelCy = sym.y + optCy;
     availH = sym.h;
   } else if (isInductionType(sym.symbolId)) {
     const stripTopY = sym.y + sym.h * INDUCTION_CONFIG.stripTopFrac;