Improve attachment memory safety, downloads, and high-memory alert UX.

Stream large receives to disk with chunk acks to cap renderer RAM, evict
off-screen display blobs, and route exports through a disk-aware download
service. Fix the high-memory dialog (backdrop dismiss, copy, log actions),
allow diagnostics paths in the path jail, and restore persisted image
hydration after reload.

Co-authored-by: Cursor <cursoragent@cursor.com>

toju-app/src/app/domains/attachment/application/services/attachment-chunk-ack.service.spec.ts

@@ -0,0 +1,37 @@
+import {
+  beforeEach,
+  describe,
+  expect,
+  it,
+  vi
+} from 'vitest';
+
+import { AttachmentChunkAckService } from './attachment-chunk-ack.service';
+
+describe('AttachmentChunkAckService', () => {
+  let service: AttachmentChunkAckService;
+
+  beforeEach(() => {
+    service = new AttachmentChunkAckService();
+  });
+
+  it('resolves a waiter when the matching chunk ack arrives', async () => {
+    const waitPromise = service.waitForAck('msg-1', 'file-1', 0, 1_000);
+
+    service.resolveAck('msg-1', 'file-1', 0);
+
+    await expect(waitPromise).resolves.toBeUndefined();
+  });
+
+  it('times out when no ack arrives', async () => {
+    vi.useFakeTimers();
+
+    const waitPromise = service.waitForAck('msg-1', 'file-1', 1, 50);
+
+    vi.advanceTimersByTime(51);
+
+    await expect(waitPromise).rejects.toThrow('attachment chunk ack timeout');
+
+    vi.useRealTimers();
+  });
+});