gtauri viewer: mid-commit touch/key takes over the swipe (chained swipes)

A second swipe while the new image was still sliding in got dropped
(pointerdown bailed while the commit tween was in flight). Now a
touch — or arrow key — during a commit takes it over: the commit
finishes instantly (roles swap at the settle positions, same
dimension-adoption path as natural completion) and the input starts a
fresh gesture on the landed image, so rapid successive swipes chain
through multiple pictures. A plain tap during a commit simply settles
it early.

Verified on the emulator: two 100 ms flicks 120 ms apart (the second
lands mid-commit) end on the exact same image — pixel-identical — as
two deliberate slow swipes.

harnesses/gtauri/frontend/dist/index.html

@@ -547,7 +547,8 @@ function tweenTo(tx, ty, ms, onDone) {
 /// the incoming one slides home while the outgoing one slides off
 /// screen; only then do the roles swap (returns false at the edges).
 function navigate(delta, vel) {
-  if (tween && tween.commit) return false; // commit already in flight
+  // Key nav during a commit takes it over the same way a touch does.
+  if (tween && tween.commit) takeover();
   const i = ids.indexOf(viewerId);
   const ni = i + delta;
   if (i < 0 || ni < 0 || ni >= ids.length) return false;
@@ -585,15 +586,24 @@ function commitTo(ni, delta, vel) {
     applyTransform();
     navLayout();
     if (t < 1) {
-      tween = { raf: requestAnimationFrame(step), commit: true };
+      tween = { raf: requestAnimationFrame(step), commit: true, target: ni };
     } else {
-      const id = ids[ni];
       tween = null;
+      finishCommit(ni);
+    }
+  };
+  tween = { raf: requestAnimationFrame(step), commit: true, target: ni };
+}
+
+/// Swap the elements' roles at the settled positions: vimg2 (the
+/// incoming image) becomes primary at 0 with its own dimensions (see
+/// the aspect note there), vimg shows it next paint, the old image is
+/// gone. Called when the commit tween completes AND on mid-flight
+/// takeover — a new touch/key during a commit finishes it instantly
+/// so the new gesture acts on the landed image (swipes chain).
+function finishCommit(ni) {
+  const id = ids[ni];
   if (nav && nav.id === id && nav.ready) {
-        // vimg2 (incoming) is exactly at 0: it becomes primary. Adopt
-        // its dimensions NOW — otherwise the new pixels render in the
-        // OLD image's width/height box (wrong aspect) until full-res
-        // lands and fitViewer() fixes it (visible stretch → snap).
     const nw = nav.w, nh = nav.h, ns = nav.scale;
     vimg.src = vimg2.src; // cached + decoded → paints immediately
     base.w = nw; base.h = nh;
@@ -606,17 +616,25 @@ function commitTo(ni, delta, vel) {
     // Hide the preview only once the primary has the bytes.
     vimg.onload = () => { if (viewerId === id) navHide(); };
   } else {
-        // Preview never made it (keyboard nav / slow thumb): plain
+    // Preview never made it (keyboard nav / slow thumb): plain open —
-        // open — the thumb round-trip sets the right dimensions.
+    // the thumb round-trip sets the right dimensions.
     openViewer(id, false);
   }
 }
-  };
+
-  tween = { raf: requestAnimationFrame(step), commit: true };
+/// Instantly settle an in-flight commit (touch/key takeover).
+function takeover() {
+  const target = tween.target;
+  cancelAnimationFrame(tween.raf);
+  tween = null;
+  finishCommit(target);
 }
 
 viewer.addEventListener("pointerdown", (e) => {
-  if (tween && tween.commit) return; // a swipe commit is in flight
+  // A touch during a swipe commit takes it over: finish the commit
+  // now and start this gesture on the landed image — a second swipe
+  // while the new image is sliding in acts as another swipe.
+  if (tween && tween.commit) takeover();
   viewer.setPointerCapture(e.pointerId);
   if (tween) { cancelAnimationFrame(tween.raf); tween = null; }
   pts.set(e.pointerId, { x: e.clientX, y: e.clientY });
@@ -716,7 +734,6 @@ const endPt = (e) => {
 viewer.addEventListener("pointerup", endPt);
 viewer.addEventListener("pointercancel", endPt);
 viewer.addEventListener("dblclick", () => {
-  if (tween && tween.commit) return;
   vScale = fitScale();
   vTx = 0; vTy = 0; vApply();
 });