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/domain/logic/attachment-blob-eviction.rules.spec.ts

@@ -0,0 +1,61 @@
+import {
+  describe,
+  expect,
+  it
+} from 'vitest';
+
+import {
+  buildAttachmentDisplayPinKey,
+  canRevokeAttachmentDisplayBlob,
+  shouldRevokeDisplayBlobForAttachment
+} from './attachment-blob-eviction.rules';
+
+describe('attachment-blob-eviction rules', () => {
+  it('builds a stable pin key from message and attachment ids', () => {
+    expect(buildAttachmentDisplayPinKey('msg-1', 'att-1')).toBe('msg-1:att-1');
+  });
+
+  it('allows revoking blob urls when a disk path can rehydrate the attachment', () => {
+    expect(canRevokeAttachmentDisplayBlob({
+      objectUrl: 'blob:http://localhost/abc',
+      savedPath: '/appdata/photo.png',
+      receivedBytes: 0,
+      available: true
+    })).toBe(true);
+  });
+
+  it('refuses to revoke blobs that are the only local copy', () => {
+    expect(canRevokeAttachmentDisplayBlob({
+      objectUrl: 'blob:http://localhost/abc',
+      receivedBytes: 0,
+      available: true
+    })).toBe(false);
+  });
+
+  it('refuses to revoke blobs while a download is still in progress', () => {
+    expect(canRevokeAttachmentDisplayBlob({
+      objectUrl: 'blob:http://localhost/abc',
+      savedPath: '/appdata/photo.png',
+      receivedBytes: 1024,
+      available: false
+    })).toBe(false);
+  });
+
+  it('skips revocation for pinned attachments', () => {
+    const attachment = {
+      id: 'att-1',
+      objectUrl: 'blob:http://localhost/abc',
+      savedPath: '/appdata/photo.png',
+      receivedBytes: 0,
+      available: true
+    };
+
+    expect(shouldRevokeDisplayBlobForAttachment(
+      'msg-1',
+      attachment,
+      new Set([buildAttachmentDisplayPinKey('msg-1', 'att-1')])
+    )).toBe(false);
+
+    expect(shouldRevokeDisplayBlobForAttachment('msg-1', attachment, new Set())).toBe(true);
+  });
+});