Revert the timeline optimistic and pagination rework (#2596)

* Add npm release track invariant and beta dist-tag procedure

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

The timeline optimistic/pagination rework needs more work than main releases can wait for. Reverted together with #2484; both are reapplied on integration/timeline-optimistic-rework.

* Revert "Stop completed turns from appearing stuck (#2484)"

See the #2490 revert. #2490 built on this submission-authority change, so the two revert and reapply as a pair.

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

@@ -1,7 +1,6 @@
 import { describe, expect, it } from "vitest";
 import {
   createImageSourceCacheKey,
-  createPreviewAttachmentId,
   fileUriToPath,
   localFileSourceToPath,
   parseDataUrl,
@@ -87,29 +86,4 @@ 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",
-      }),
-    );
-  });
 });