test(capture): expect tip-trimmed every-6in width stations

Ty UAT: width min/max must describe bulk, not tips. Pin L=48 tapered
case (7 interior stations, no tip endpoints), uniform mid-board count,
and L≤12 empty/zero fallback before the sampleWidths change lands.

frontend/src/measure/measure.test.ts

@@ -0,0 +1,58 @@
+import { test } from 'node:test';
+import assert from 'node:assert/strict';
+import { minAreaRect, orientedRect } from '../geometry/rect.ts';
+import { measure } from './measure.ts';
+
+// Uniform slab, 10 px/in: full W×H canvas, axis +x via minAreaRect angle 0.
+function uniform(W: number, H: number) {
+  const bitset = new Uint8Array(W * H).fill(1);
+  const box = orientedRect(minAreaRect(bitset, W, H)!, 0);
+  return { bitset, box, slabPx: W * H };
+}
+
+// Tapered slab, 10 px/in: tips under 6 in and past L−6 in are `tipPx` wide
+// (centered), the bulk is full canvas height.
+function tapered(W: number, H: number, lengthEighths: number, tipPx: number) {
+  const inIn = W / 10;
+  const bitset = new Uint8Array(W * H);
+  const half = tipPx / 2;
+  for (let x = 0; x < W; x++) {
+    const p = x / 10;
+    const w = p < 6 || p > inIn - 6 ? tipPx : H;
+    for (let y = (H - w) / 2; y < (H + w) / 2; y++) bitset[y * W + x] = 1;
+  }
+  const box = orientedRect(minAreaRect(bitset, W, H)!, 0);
+  return { bitset, box, slabPx: bitset.reduce((a, c) => a + c, 0), lengthEighths };
+}
+
+test('tapered 48in slab: min/max reflect the bulk, tips excluded', () => {
+  const { bitset, box, slabPx, lengthEighths } = tapered(480, 100, 384, 20); // tips 2in, bulk 10in
+  const m = measure(bitset, 480, 100, box, lengthEighths, 8, slabPx);
+  assert.equal(m.widths.every6In.length, 7, `stations ${m.widths.every6In.length} (6..42in)`);
+  for (const e of m.widths.every6In) {
+    assert.ok(e >= 76 && e <= 84, `station ${e / 8}in must be bulk (~10in)`);
+  }
+  assert.ok(m.widths.min >= 76 && m.widths.min <= 84, `min ${m.widths.min / 8}in`);
+  assert.ok(m.widths.max >= 76 && m.widths.max <= 84, `max ${m.widths.max / 8}in`);
+});
+
+test('uniform slab: interior stations keep the full width', () => {
+  const { bitset, box, slabPx } = uniform(480, 100);
+  const m = measure(bitset, 480, 100, box, 384, 8, slabPx);
+  assert.equal(m.widths.every6In.length, 7);
+  for (const e of m.widths.every6In) {
+    assert.ok(e >= 72 && e <= 104, `station ${e / 8}in`);
+  }
+});
+
+test('short slab L=12in: no interior stations, widths are empty/zero', () => {
+  const { bitset, box, slabPx } = uniform(120, 100);
+  const m = measure(bitset, 120, 100, box, 96, 8, slabPx);
+  assert.deepEqual(m.widths, { min: 0, max: 0, avg: 0, every6In: [] });
+});
+
+test('short slab L=10in: no interior stations, widths are empty/zero', () => {
+  const { bitset, box, slabPx } = uniform(100, 100);
+  const m = measure(bitset, 100, 100, box, 80, 8, slabPx);
+  assert.deepEqual(m.widths, { min: 0, max: 0, avg: 0, every6In: [] });
+});