feat(capture): shared crop_fill + tape geometry for #99

- One crop_fill (default 0.9) replaces duplicated FILL in inventory/overlay
- Thin localStorage settings store; crop % only moves long-axis end insets
- Pure tapeGeometry: fixed stage line, stage↔image map, tick span → px
- measure() prefers tape tick span for scale; maskSpanAlong demoted
- rotateCalibration bakes cal tilt into inventory + overlay only
- Fix stale 80%-fill comment on slabBounds

frontend/src/capture/tapeGeometry.test.ts

@@ -0,0 +1,53 @@
+import { test } from 'node:test';
+import assert from 'node:assert/strict';
+import {
+  STAGE_H, STAGE_W, clampTickPair, containFit, defaultTape, defaultTicks,
+  lineX, stageToImage, tapeEndpoints,
+} from './tapeGeometry.ts';
+import { cropMarginFraction, DEFAULT_CROP_FILL } from '../png/crop.ts';
+
+test('defaultTicks sit at crop insets for 90% fill', () => {
+  const t = defaultTicks(0.9);
+  const inset = STAGE_H * cropMarginFraction(0.9);
+  assert.ok(Math.abs(t.tickA - inset) < 1e-9);
+  assert.ok(Math.abs(t.tickB - (STAGE_H - inset)) < 1e-9);
+});
+
+test('lineX is the middle of the 3:4 stage', () => {
+  assert.equal(lineX(), STAGE_W / 2);
+});
+
+test('identity tape: stage centre maps near image centre', () => {
+  const imgW = 480, imgH = 640;
+  const tape = defaultTape(DEFAULT_CROP_FILL, 0);
+  const [ix, iy] = stageToImage(STAGE_W / 2, STAGE_H / 2, tape, imgW, imgH);
+  assert.ok(Math.abs(ix - imgW / 2) < 1e-6, `ix=${ix}`);
+  assert.ok(Math.abs(iy - imgH / 2) < 1e-6, `iy=${iy}`);
+});
+
+test('tapeEndpoints span equals tick distance in image px at identity (matching aspect)', () => {
+  const imgW = 480, imgH = 640;
+  const tape = defaultTape(0.9, 0);
+  const ep = tapeEndpoints(tape, imgW, imgH);
+  const { scale0 } = containFit(imgW, imgH);
+  const expected = Math.abs(tape.tickB - tape.tickA) / scale0;
+  assert.ok(Math.abs(ep.spanPx - expected) < 1e-6, `span ${ep.spanPx} vs ${expected}`);
+  // Direction should be +y (down the stage → down the image)
+  assert.ok(Math.abs(ep.ux) < 1e-6, `ux=${ep.ux}`);
+  assert.ok(ep.uy > 0.99, `uy=${ep.uy}`);
+});
+
+test('zoom scales inverse: 2× zoom halves image-space tick span', () => {
+  const imgW = 480, imgH = 640;
+  const base = defaultTape(0.9, 0);
+  const zoomed = { ...base, zoom: 2 };
+  const a = tapeEndpoints(base, imgW, imgH).spanPx;
+  const b = tapeEndpoints(zoomed, imgW, imgH).spanPx;
+  assert.ok(Math.abs(b * 2 - a) < 1e-6, `base=${a} zoomed=${b}`);
+});
+
+test('clampTickPair enforces gap and order', () => {
+  const p = clampTickPair(400, 100, 40);
+  assert.ok(p.tickB - p.tickA >= 40);
+  assert.ok(p.tickA <= p.tickB);
+});