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/ai-operation.js

@@ -0,0 +1,45 @@
+// Capture repeat clicks before tool handlers can start another request.
+export function beginAIOperation(button, onCancel) {
+  const controller = new AbortController();
+  const title = button.title;
+  button.disabled = false;
+  button.title = 'Cancel running action';
+  button.setAttribute('aria-busy', 'true');
+  const cancel = event => {
+    event.preventDefault();
+    event.stopImmediatePropagation();
+    if (!controller.signal.aborted) {
+      controller.abort();
+      onCancel?.();
+    }
+  };
+  button.addEventListener('click', cancel, true);
+  return {
+    signal: controller.signal,
+    finish() {
+      button.removeEventListener('click', cancel, true);
+      button.title = title;
+      button.removeAttribute('aria-busy');
+    },
+  };
+}
+
+export function decodeAIImage(base64, signal) {
+  return new Promise((resolve, reject) => {
+    const image = new Image();
+    const cleanup = () => {
+      image.onload = image.onerror = null;
+      signal.removeEventListener('abort', abort);
+    };
+    const abort = () => {
+      cleanup();
+      image.src = '';
+      reject(new DOMException('Cancelled', 'AbortError'));
+    };
+    if (signal.aborted) { abort(); return; }
+    signal.addEventListener('abort', abort, { once: true });
+    image.onload = () => { cleanup(); resolve(image); };
+    image.onerror = () => { cleanup(); reject(new Error('Failed to decode result image')); };
+    image.src = base64.startsWith('data:') ? base64 : 'data:image/png;base64,' + base64;
+  });
+}