Preserve preview harness, editor, email and task improvements

Snapshot current maintainer-preview application changes and regression fixtures for integration into lab. Excludes local runtime data, evaluation outputs and source backups. Focused Python regression selection: 140 passed; full suite not certified.

static/js/editor/history-budget.js

@@ -7,6 +7,53 @@ function imageDataBytes(imageData) {
   return Number(imageData?.data?.byteLength || imageData?.data?.length || 0);
 }
 
+function pixelSlots(snapshot) {
+  const slots = [];
+  const add = (object, key = 'imageData') => { if (object?.[key]) slots.push([object, key]); };
+  add(snapshot?.wand); add(snapshot?.lastSelection);
+  for (const item of snapshot?.savedSelections || []) add(item);
+  for (const group of snapshot?.layerGroups || []) {
+    for (const mask of group.masks || []) add(mask);
+    for (const effect of group.effects || []) add(effect.mask);
+  }
+  for (const layer of snapshot?.layers || []) {
+    add(layer); add(layer.placed, 'sourceImageData');
+    for (const mask of layer.masks || []) add(mask);
+    for (const effect of layer.effects || []) add(effect.mask);
+  }
+  return slots;
+}
+
+export function shareSnapshotPixels(snapshot, previous) {
+  if (!previous) return snapshot;
+  const candidates = pixelSlots(previous).map(([object, key]) => object[key]);
+  for (const [object, key] of pixelSlots(snapshot)) {
+    const image = object[key];
+    const match = candidates.find(other => {
+      if (image === other) return true;
+      if (image.width !== other.width || image.height !== other.height || image.data.length !== other.data.length) return false;
+      for (let i = 0; i < image.data.length; i++) if (image.data[i] !== other.data[i]) return false;
+      return true;
+    });
+    if (match) object[key] = match;
+  }
+  return snapshot;
+}
+
+export function historyByteSize(stack) {
+  const buffers = new Set();
+  let bytes = 0;
+  for (const snapshot of stack) {
+    const slots = pixelSlots(snapshot);
+    if (!slots.length) { bytes += snapshotByteSize(snapshot); continue; }
+    for (const [object, key] of slots) {
+      const image = object[key], buffer = image.data.buffer || image.data;
+      if (!buffers.has(buffer)) { buffers.add(buffer); bytes += buffer.byteLength || imageDataBytes(image); }
+    }
+  }
+  return bytes;
+}
+
 export function snapshotByteSize(snapshot) {
   if (!snapshot) return 0;
   if (Number.isFinite(snapshot._bytes)) return snapshot._bytes;
@@ -30,10 +77,11 @@ export function trimHistoryStack(
   maxBytes = MAX_HISTORY_BYTES,
 ) {
   while (stack.length > maxEntries) stack.shift();
-  let bytes = stack.reduce((total, snapshot) => total + snapshotByteSize(snapshot), 0);
+  let bytes = historyByteSize(stack);
   // Keep the newest state even when one snapshot alone exceeds the budget.
   while (stack.length > 1 && bytes > maxBytes) {
-    bytes -= snapshotByteSize(stack.shift());
+    stack.shift();
+    bytes = historyByteSize(stack);
   }
   return bytes;
 }