fix(capture): ±90° tilt slider midpoint + two-finger rotate

Clamp tape tilt to [-90, 90] so the slider knob starts centered and
CCW works. PhotoStage pinch now tracks angle as well as zoom.

frontend/src/capture/AxisPanel.svelte

@@ -1,7 +1,7 @@
 <script lang="ts">
   import type { Capture } from './capture.types';
   import type { TapeTransform } from './tapeGeometry';
-  import { defaultTicks } from './tapeGeometry';
+  import { clampTiltDeg, defaultTicks } from './tapeGeometry';
   import PhotoStage from './PhotoStage.svelte';
   import { getCropFill, setCropFill } from '../settings/cropFill';
   import { cropMarginFraction } from '../png/crop';
@@ -21,13 +21,14 @@
   const onTapeChange = (t: TapeTransform) => setTape(t);
 
   const nudgeTilt = (delta: number) => {
-    setTape({ ...tape, tiltDeg: tape.tiltDeg + delta });
+    setTape({ ...tape, tiltDeg: clampTiltDeg(tape.tiltDeg + delta) });
   };
 
   const setTilt = (deg: number) => {
-    setTape({ ...tape, tiltDeg: deg });
+    const clamped = clampTiltDeg(deg);
+    setTape({ ...tape, tiltDeg: clamped });
     // Keep legacy path warm for any callers still using setAxisAngle.
-    setAxisAngle(deg);
+    setAxisAngle(clamped);
   };
 
   const nudgeZoom = (dir: number) => {
@@ -67,14 +68,14 @@
       <div class="angle">
         <button type="button" class="thumb" aria-label="Tilt left" on:click={() => nudgeTilt(-1)}>−</button>
         <input
-          type="range" min="0" max="359" step="0.1"
+          type="range" min="-90" max="90" step="0.1"
-          value={((tiltShown % 360) + 360) % 360}
+          value={clampTiltDeg(tiltShown)}
           on:input={(e) => setTilt(Number(e.currentTarget.value))}
         />
         <button type="button" class="thumb" aria-label="Tilt right" on:click={() => nudgeTilt(1)}>+</button>
         <span class="val">{tiltShown}°</span>
       </div>
-      <p class="nudge">← → tilt 1° · Shift+← → 0.1° · or drag the ↻ handle</p>
+      <p class="nudge">±90° · ← → tilt 1° · Shift+← → 0.1° · two-finger twist · or drag the ↻ handle</p>
     </div>
 
     <div>

frontend/src/capture/PhotoStage.svelte

@@ -2,7 +2,7 @@
   import { onDestroy, onMount, tick } from 'svelte';
   import type { BBox } from './capture.types';
   import type { TapeTransform } from './tapeGeometry';
-  import { STAGE_H, STAGE_W, clampTickPair, defaultTicks, lineX } from './tapeGeometry';
+  import { STAGE_H, STAGE_W, clampTickPair, clampTiltDeg, defaultTicks, lineX } from './tapeGeometry';
   import { fitDisplay } from './fitDisplay';
   import { decodeOrientedBitmap } from '../decodeOrientedBitmap';
   import { cropMarginFraction } from '../png/crop';
@@ -144,6 +144,8 @@
   let pointers = new Map<number, { x: number; y: number }>();
   let pinchStartDist = 0;
   let pinchStartZoom = 1;
+  let pinchStartAngle = 0;
+  let pinchStartTilt = 0;
 
   const stagePoint = (clientX: number, clientY: number): { x: number; y: number } => {
     const el = tapeWrap;
@@ -176,8 +178,12 @@
     pointers.set(e.pointerId, { x: e.clientX, y: e.clientY });
     if (pointers.size === 2) {
       const pts = [...pointers.values()];
-      pinchStartDist = Math.hypot(pts[0].x - pts[1].x, pts[0].y - pts[1].y) || 1;
+      const dx = pts[1].x - pts[0].x;
+      const dy = pts[1].y - pts[0].y;
+      pinchStartDist = Math.hypot(dx, dy) || 1;
       pinchStartZoom = live.zoom;
+      pinchStartAngle = Math.atan2(dy, dx);
+      pinchStartTilt = live.tiltDeg;
       drag = null;
       return;
     }
@@ -200,9 +206,14 @@
     if (pointers.has(e.pointerId)) pointers.set(e.pointerId, { x: e.clientX, y: e.clientY });
     if (pointers.size === 2) {
       const pts = [...pointers.values()];
-      const dist = Math.hypot(pts[0].x - pts[1].x, pts[0].y - pts[1].y) || 1;
+      const dx = pts[1].x - pts[0].x;
+      const dy = pts[1].y - pts[0].y;
+      const dist = Math.hypot(dx, dy) || 1;
       const z = Math.min(3, Math.max(0.5, pinchStartZoom * (dist / pinchStartDist)));
-      emit({ ...live, zoom: z });
+      // Screen y-down atan2 delta matches CSS rotate (positive = clockwise).
+      const angle = Math.atan2(dy, dx);
+      const deltaDeg = ((angle - pinchStartAngle) * 180) / Math.PI;
+      emit({ ...live, zoom: z, tiltDeg: clampTiltDeg(pinchStartTilt + deltaDeg) });
       return;
     }
     if (!drag) return;
@@ -220,7 +231,7 @@
       const a0 = Math.atan2(drag.y0 - cy, drag.x0 - cx);
       const a1 = Math.atan2(p.y - cy, p.x - cx);
       const delta = ((a1 - a0) * 180) / Math.PI;
-      emit({ ...live, tiltDeg: drag.tilt0 + delta });
+      emit({ ...live, tiltDeg: clampTiltDeg(drag.tilt0 + delta) });
     }
   };
 
@@ -243,7 +254,7 @@
       e.preventDefault();
       const step = fine ? 0.1 : 1;
       const dir = e.key === 'ArrowLeft' ? -1 : 1;
-      emit({ ...live, tiltDeg: live.tiltDeg + dir * step });
+      emit({ ...live, tiltDeg: clampTiltDeg(live.tiltDeg + dir * step) });
     } else if (e.key === 'ArrowUp' || e.key === 'ArrowDown') {
       e.preventDefault();
       const step = fine ? 0.1 : 1;

frontend/src/capture/session.ts

@@ -12,7 +12,7 @@ import { encodeInventoryPng, type InventoryInput } from '../png/inventory';
 import { encodeOverlayPng, type EncodeOverlayInput } from '../png/overlay';
 import { rotateCalibration } from '../png/rotateCal';
 import { decodeOrientedBitmap } from '../decodeOrientedBitmap';
-import { defaultTape, tapeEndpoints, type TapeTransform } from './tapeGeometry';
+import { clampTiltDeg, defaultTape, tapeEndpoints, type TapeTransform } from './tapeGeometry';
 import { getCropFill } from '../settings/cropFill';
 import type { TapeLine } from './capture.types';
 
@@ -323,7 +323,7 @@ export function createCaptureSession(opts: SessionOpts = {}): CaptureSession {
       return { ...d.tape };
     }
     // Seed tilt so the mask long side sits near vertical under the fixed line.
-    const seedTilt = 90 - bbox.angleDeg;
+    const seedTilt = clampTiltDeg(90 - bbox.angleDeg);
     const t = defaultTape(getCropFill(), seedTilt);
     const ep = w > 0 && h > 0 ? tapeEndpoints(t, w, h) : { spanPx: 0, start: [0, 0] as [number, number], end: [0, 0] as [number, number], ux: 0, uy: 1 };
     return { ...t, spanPx: ep.spanPx };
@@ -338,7 +338,7 @@ export function createCaptureSession(opts: SessionOpts = {}): CaptureSession {
       : bbox.angleDeg;
     const nextBbox = orientedRect(bbox, angleDeg);
     const line: TapeLine = {
-      tiltDeg: tape.tiltDeg,
+      tiltDeg: clampTiltDeg(tape.tiltDeg),
       zoom: tape.zoom,
       panX: tape.panX,
       panY: tape.panY,
@@ -534,7 +534,7 @@ export function createCaptureSession(opts: SessionOpts = {}): CaptureSession {
       };
       const w = state.source.widthPx;
       const h = state.source.heightPx;
-      const seedTilt = 90 - bbox.angleDeg;
+      const seedTilt = clampTiltDeg(90 - bbox.angleDeg);
       const tape0 = defaultTape(getCropFill(), seedTilt);
       const axis = axisWithTape(bbox, tape0, w, h);
       set({ k: 'axis', source: state.source, approvedMask: overlay, axis });
@@ -544,7 +544,7 @@ export function createCaptureSession(opts: SessionOpts = {}): CaptureSession {
     // Legacy slider path — maps to photo tilt under the fixed tape line (#99).
     setAxisAngle(deg: number) {
       if (state.k !== 'axis') return;
-      const tape = { ...state.axis.tape, tiltDeg: deg };
+      const tape = { ...state.axis.tape, tiltDeg: clampTiltDeg(deg) };
       const axis = axisWithTape(state.axis.bbox, tape, state.source.widthPx, state.source.heightPx);
       set({ ...state, axis });
       void persist();
@@ -552,7 +552,8 @@ export function createCaptureSession(opts: SessionOpts = {}): CaptureSession {
 
     setTape(tape: TapeTransform) {
       if (state.k !== 'axis') return;
-      const axis = axisWithTape(state.axis.bbox, tape, state.source.widthPx, state.source.heightPx);
+      const clamped = { ...tape, tiltDeg: clampTiltDeg(tape.tiltDeg) };
+      const axis = axisWithTape(state.axis.bbox, clamped, state.source.widthPx, state.source.heightPx);
       set({ ...state, axis });
       void persist();
     },

frontend/src/capture/tapeGeometry.test.ts

@@ -1,8 +1,8 @@
 import { test } from 'node:test';
 import assert from 'node:assert/strict';
 import {
-  STAGE_H, STAGE_W, clampTickPair, containFit, defaultTape, defaultTicks,
+  STAGE_H, STAGE_W, TILT_MAX, TILT_MIN, clampTickPair, clampTiltDeg, containFit,
-  lineX, stageToImage, tapeEndpoints,
+  defaultTape, defaultTicks, lineX, stageToImage, tapeEndpoints,
 } from './tapeGeometry.ts';
 import { cropMarginFraction, DEFAULT_CROP_FILL } from '../png/crop.ts';
 
@@ -51,3 +51,21 @@ test('clampTickPair enforces gap and order', () => {
   assert.ok(p.tickB - p.tickA >= 40);
   assert.ok(p.tickA <= p.tickB);
 });
+
+test('clampTiltDeg clamps to ±90', () => {
+  assert.equal(TILT_MIN, -90);
+  assert.equal(TILT_MAX, 90);
+  assert.equal(clampTiltDeg(0), 0);
+  assert.equal(clampTiltDeg(45.5), 45.5);
+  assert.equal(clampTiltDeg(-45.5), -45.5);
+  assert.equal(clampTiltDeg(90), 90);
+  assert.equal(clampTiltDeg(-90), -90);
+  assert.equal(clampTiltDeg(91), 90);
+  assert.equal(clampTiltDeg(-100), -90);
+  assert.equal(clampTiltDeg(Number.NaN), 0);
+});
+
+test('defaultTape clamps seed tilt', () => {
+  assert.equal(defaultTape(0.9, 120).tiltDeg, 90);
+  assert.equal(defaultTape(0.9, -200).tiltDeg, -90);
+});

frontend/src/capture/tapeGeometry.ts

@@ -9,6 +9,15 @@ import { cropMarginFraction, DEFAULT_CROP_FILL } from '../png/crop';
 export const STAGE_W = 480;
 export const STAGE_H = 640;
 
+/** Interactive tilt limits (degrees). Slider midpoint = 0; both ways ±90. */
+export const TILT_MIN = -90;
+export const TILT_MAX = 90;
+
+export function clampTiltDeg(deg: number): number {
+  if (!Number.isFinite(deg)) return 0;
+  return Math.min(TILT_MAX, Math.max(TILT_MIN, deg));
+}
+
 export interface TapeTransform {
   /** Photo tilt in degrees (CSS-style; positive = clockwise). */
   tiltDeg: number;
@@ -29,7 +38,7 @@ export function defaultTicks(fill: number = DEFAULT_CROP_FILL): { tickA: number;
 export function defaultTape(fill: number = DEFAULT_CROP_FILL, seedTiltDeg = 0): TapeTransform {
   const t = defaultTicks(fill);
   return {
-    tiltDeg: seedTiltDeg,
+    tiltDeg: clampTiltDeg(seedTiltDeg),
     zoom: 1,
     panX: 0,
     panY: 0,