fix(editor): snap dragged barlines to chart-time onsets (fixes #254)

src/tempo.js

@@ -20,7 +20,7 @@
 // Browser surface: `ctx` (the shared 2D context) plus the sync-inspector and
 // time-signature controls it builds into the toolbar.
 // ════════════════════════════════════════════════════════════════════
-import { _ensureOnsets, _ensureOnsetsShifted, _nearestOnsetTimePure } from './audio.js';
+import { _ensureOnsetsShifted, _nearestOnsetTimePure } from './audio.js';
 import { _localTempoSeriesPure, _segmentRoughMapPure, _segmentTempoPure } from './tempo-segment.js';
 import { beatOf, timeOf } from './beats.js';
 import { DPR, canvas, ctx } from './canvas.js';
@@ -2514,7 +2514,11 @@ export function _tempoMapOnDragMove(x) {
     dg.snappedT = null;
     if (S.snapMode === 'onset' && !(orig[d] && orig[d].locked)) {
         const tol = _tempoOnsetSnapTolPure(xToTime(1) - xToTime(0), ONSET_SNAP_PX, ONSET_SNAP_MAX_S);
-        const res = _tempoOnsetSnapPure(rawT, _ensureOnsets(), tol, loBound, hiBound);
+        // rawT and the barlines are CHART time, so the snap must compare against
+        // CHART-time onsets — _ensureOnsetsShifted() (matching Suggest-fit), not the
+        // buffer-time _ensureOnsets(): with the audio shifted the two diverge and the
+        // barline would snap to the un-shifted attack (issue #254).
+        const res = _tempoOnsetSnapPure(rawT, _ensureOnsetsShifted(), tol, loBound, hiBound);
         newT = res.t;
         if (res.snapped) dg.snappedT = newT;
     }

tests/tempo_onset_snap.test.mjs

@@ -72,7 +72,8 @@ t('the drag move gates onset-snap on Snap = Onset and a non-locked pole', () =>
     const b = body('export function _tempoMapOnDragMove', 'export function _tempoMapOnDragEnd');
     assert.match(b, /S\.snapMode === 'onset'/, 'only snaps in Onset mode');
     assert.match(b, /!\(orig\[d\] && orig\[d\]\.locked\)/, 'locked poles never snap');
-    assert.match(b, /_tempoOnsetSnapPure\(rawT, _ensureOnsets\(\)/, 'uses the live onset cache');
+    assert.match(b, /_tempoOnsetSnapPure\(rawT, _ensureOnsetsShifted\(\)/,
+        'snaps against CHART-time onsets (shift-corrected), matching Suggest-fit — issue #254');
 });
 t('the drag end reports a snap', () => {
     const b = body('export function _tempoMapOnDragEnd', 'export function _makeTimeRemap');