Show the pre-edit values while the finger holds, and pass the FRAME tab flag

Pressing and holding on the picture with the LIGHT/WB/FX panel open now
rewinds the last edit, and the panel rewinds with it: the chip numbers and
the open slider read the same pre-edit snapshot, so before and after can be
compared by eye and not just by looking at the picture. Only the displayed
values move -- the stored adjustments, RECIPE and the export keep the real
ones, and a gap longer than PEEK_GAP_MS starts a new snapshot for the next
gesture.

Also pass frameTabActive, without which the FRAME preview zoom added in
Viewfinder.tsx could never turn on.

App.tsx

@@ -578,6 +578,30 @@ export default function App() {
     cropRatio !== 'none' ||
     differs(cropRect, DEFAULT_CROP_RECT);
 
+  // ---- Hold-to-compare -----------------------------------------------------
+  // While a LIGHT/WB/FX panel is open, pressing and holding on the picture
+  // shows it with the last edit undone, so the user can flick between before
+  // and after. The picture and the parameter display both follow the peek;
+  // the stored values, RECIPE and the export never move.
+  const PEEK_GAP_MS = 700; // a longer pause = a new gesture, so re-snapshot
+  const peekRef = useRef<{ before: ColorAdjustments | null; at: number }>({
+    before: null,
+    at: 0,
+  });
+  const [peekAdjustments, setPeekAdjustments] = useState<ColorAdjustments | null>(null);
+  const peekArmed = openTab === 'iq' || openTab === 'wb' || openTab === 'filters';
+  const handleComparePeek = useCallback((on: boolean) => {
+    setPeekAdjustments(on ? peekRef.current.before : null);
+  }, []);
+  // The values the panel and the picture SHOW. While the finger is down they
+  // fall back to the pre-edit snapshot, so the chip numbers and the open slider
+  // travel back with the picture and the before/after is readable, not just
+  // visible. The real values stay untouched: writes, RECIPE and the on-image
+  // drag baseline all keep reading `adjustments`.
+  const shownAdjustments = peekArmed && peekAdjustments ? peekAdjustments : adjustments;
+  const withPeek = (r: Recipe): Recipe =>
+    shownAdjustments === r.adjustments ? r : { ...r, adjustments: shownAdjustments };
+
   const handleUpdateAdjustments = (updates: Partial<ColorAdjustments>) => {
     // Storm guard, generic across every param: same-value writes (slider
     // micro-jitter / repeated pointer-move events) still build a fresh
@@ -586,6 +610,15 @@ export default function App() {
     // skipped identical EV needs no re-send.
     const keys = Object.keys(updates) as (keyof ColorAdjustments)[];
     if (keys.every((k) => updates[k] === adjustments[k])) return;
+    // Remember where THIS edit started. A pause longer than PEEK_GAP_MS counts
+    // as a new gesture, so the snapshot is retaken; within one drag the earlier
+    // value survives and the peek shows the drag's own starting point.
+    // ponytail: a >700ms stall in the middle of one drag re-snapshots mid-way.
+    const peekNow = Date.now();
+    if (peekNow - peekRef.current.at > PEEK_GAP_MS) {
+      peekRef.current.before = adjustments;
+    }
+    peekRef.current.at = peekNow;
     // B8: never call a setState inside another setState's updater.
     const next = { ...adjustments, ...updates };
     setAdjustments(next);
@@ -1300,7 +1333,7 @@ export default function App() {
           ref={viewfinderRef}
           mode={mode}
           facing={cameraFacing}
-          recipe={
+          recipe={withPeek(
             selectedRecipe || {
               id: 'temp',
               name: 'Custom',
@@ -1309,7 +1342,7 @@ export default function App() {
               frameId: selectedFrame,
               useGeotag,
             }
-          }
+          )}
           selectedFrame={selectedFrame}
           useGeotag={useGeotag}
           gpsInfo={gpsInfo}
@@ -1331,6 +1364,7 @@ export default function App() {
           onExposureChange={(ev) => handleUpdateAdjustments({ exposureCompensation: ev })}
           meteringAdjustments={meteringAdj}
           imageAdjustTarget={imageAdjustTarget}
+          onComparePeek={peekArmed ? handleComparePeek : undefined}
           customWm={customWm}
           wmRotation={wmRotation}
           gpsWm={gpsWm}
@@ -1340,6 +1374,7 @@ export default function App() {
           // The mark only captures image touches while its panel is open, so a
           // watermark left ON cannot block tap-to-focus or pinch/zoom.
           wmEditing={openTab === 'frame' && wmPanelOpen}
+          frameTabActive={openTab === 'frame'}
           onWmPositionChange={(x, y) => setCustomWm((p) => ({ ...p, x, y }))}
           onWmEdit={() => {
             // Double-tap on the mark re-opens its editor (and with it the
@@ -1381,7 +1416,7 @@ export default function App() {
               activeTab={openTab}
               recipes={recipes}
               currentRecipeId={selectedRecipe?.id || ''}
-              adjustments={adjustments}
+              adjustments={shownAdjustments}
               onResetAll={handleResetAll}
               resetDirty={resetDirty}
               selectedFrame={selectedFrame}