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/utils/assistant-image-metadata.test.ts

@@ -3,6 +3,7 @@ import {
   clearAssistantImageMetadataCache,
   estimateAssistantMessageHeightFromCache,
   extractAssistantImageSources,
+  getAssistantImageLoadStateFromMetadata,
   getAssistantImageMetadata,
   setAssistantImageMetadata,
 } from "./assistant-image-metadata";
@@ -41,6 +42,23 @@ describe("assistant image metadata", () => {
     });
   });
 
+  it("maps missing metadata to the image loading state", () => {
+    expect(getAssistantImageLoadStateFromMetadata(null)).toEqual({ status: "loading" });
+  });
+
+  it("maps cached metadata to the image ready state", () => {
+    expect(
+      getAssistantImageLoadStateFromMetadata({
+        width: 900,
+        height: 1600,
+        aspectRatio: 9 / 16,
+      }),
+    ).toEqual({
+      status: "ready",
+      aspectRatio: 9 / 16,
+    });
+  });
+
   it("estimates assistant message height from cached image metadata", () => {
     setAssistantImageMetadata(
       {