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.ts

@@ -0,0 +1,47 @@
+import { Injectable } from '@angular/core';
+
+import { buildAttachmentChunkAckKey } from '../../domain/logic/attachment-chunk-ack.rules';
+
+@Injectable({ providedIn: 'root' })
+export class AttachmentChunkAckService {
+  private readonly waiters = new Map<string, () => void>();
+
+  waitForAck(
+    messageId: string,
+    fileId: string,
+    index: number,
+    timeoutMs = 60_000
+  ): Promise<void> {
+    const key = buildAttachmentChunkAckKey(messageId, fileId, index);
+
+    return new Promise((resolve, reject) => {
+      const timer = setTimeout(() => {
+        this.waiters.delete(key);
+        reject(new Error('attachment chunk ack timeout'));
+      }, timeoutMs);
+
+      this.waiters.set(key, () => {
+        clearTimeout(timer);
+        this.waiters.delete(key);
+        resolve();
+      });
+    });
+  }
+
+  resolveAck(messageId: string, fileId: string, index: number): void {
+    this.waiters.get(buildAttachmentChunkAckKey(messageId, fileId, index))?.();
+  }
+
+  cancelPendingForFile(messageId: string, fileId: string): void {
+    const prefix = `${messageId}:${fileId}:`;
+
+    for (const [key, resolve] of this.waiters) {
+      if (!key.startsWith(prefix)) {
+        continue;
+      }
+
+      resolve();
+      this.waiters.delete(key);
+    }
+  }
+}