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/emailReplyStream.js

@@ -0,0 +1,30 @@
+export async function readEmailReplyResponse(response, onReply) {
+  if (!response.ok) throw new Error(`AI reply service returned HTTP ${response.status}`);
+  if (!response.headers.get('content-type')?.includes('text/event-stream')) return response.json();
+  const reader = response.body.getReader();
+  const decoder = new TextDecoder();
+  let buffer = '';
+  try {
+    while (true) {
+      const { value, done } = await reader.read();
+      buffer += decoder.decode(value || new Uint8Array(), { stream: !done });
+      let boundary;
+      while ((boundary = buffer.indexOf('\n\n')) !== -1) {
+        const frame = buffer.slice(0, boundary);
+        buffer = buffer.slice(boundary + 2);
+        for (const line of frame.split('\n')) {
+          if (!line.startsWith('data: ')) continue;
+          const event = JSON.parse(line.slice(6));
+          if (event.type === 'reply' && onReply(event.text) === false) {
+            throw new Error('Draft was edited or closed; AI insertion stopped');
+          }
+          if (event.type === 'result') return event;
+        }
+      }
+      if (done) throw new Error('AI reply connection ended before completion');
+    }
+  } finally {
+    await reader.cancel();
+    reader.releaseLock();
+  }
+}