Keep older chat history and image previews stable (#2490)

* fix(app): keep timeline history and previews stable

Treat persisted timeline replicas as display-only so authoritative pagination always comes from the daemon. Require renewed user intent between older-history pages unless the viewport genuinely remains at the history edge.

Model assistant image acquisition as loading, loaded, or failed so recreating a preview URL cannot be rendered as an error.

* fix(app): keep file image previews current

* fix(app): stabilize history pagination edges

* fix(app): recover transient timeline loads

* fix(app): retain assistant image previews

* Stabilize history pagination lifecycle

* Stabilize history settlement and image previews

* Retry file images after reconnect

* Keep active previews and pagination requests alive

* Replace image hook tests with typed ports

* Integrate timeline hydration with submission authority

* Harden pre-hydration timeline reconciliation

* Make rewind E2E use real scroll intent

* Preserve live timeline state through hydration

* Keep mounted image attachments retained

* Protect preview persistence and lifecycle hydration

* Preserve idless live assistant continuations

* Preserve timeline rows across delayed hydration

* test(app): cover real assistant image files

* Preserve assistant tool ordering during hydration

packages/app/src/attachments/utils.test.ts

@@ -1,6 +1,7 @@
 import { describe, expect, it } from "vitest";
 import {
   createImageSourceCacheKey,
+  createPreviewAttachmentId,
   fileUriToPath,
   localFileSourceToPath,
   parseDataUrl,
@@ -86,4 +87,29 @@ describe("parseImageDataUrl", () => {
   it("ignores SVG data URLs", () => {
     expect(parseImageDataUrl("data:image/svg+xml;base64,PHN2ZyAvPg==")).toBeNull();
   });
+
+  it("distinguishes image data that differs only in the middle", () => {
+    const prefix = "a".repeat(64);
+    const suffix = "z".repeat(64);
+    const first = `data:image/png;base64,${prefix}${"b".repeat(256)}${suffix}`;
+    const second = `data:image/png;base64,${prefix}${"c".repeat(256)}${suffix}`;
+
+    expect(createImageSourceCacheKey(first)).not.toBe(createImageSourceCacheKey(second));
+  });
+
+  it("gives equal-length preview content distinct attachment identities", () => {
+    expect(
+      createPreviewAttachmentId({
+        mimeType: "image/png",
+        contentLength: 512,
+        contentKey: "first-content",
+      }),
+    ).not.toBe(
+      createPreviewAttachmentId({
+        mimeType: "image/png",
+        contentLength: 512,
+        contentKey: "second-content",
+      }),
+    );
+  });
 });