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/stores/session-store.test.ts

@@ -5,11 +5,9 @@ import type { WorkspaceDescriptorPayload } from "@getpaseo/protocol/messages";
 
 import {
   normalizeWorkspaceDescriptor,
-  selectAgentTimelineState,
   useSessionStore,
   type WorkspaceDescriptor,
 } from "./session-store";
-import type { StreamItem } from "../types/stream";
 import { patchWorkspaceScripts } from "../contexts/session-workspace-scripts";
 
 function createWorkspace(
@@ -55,54 +53,6 @@ function getTestSessionReferences() {
   };
 }
 
-describe("agent timeline state", () => {
-  it("commits canonical items, range, and older availability as one synced state", () => {
-    initializeTestSession();
-    const items: StreamItem[] = [
-      {
-        kind: "assistant_message",
-        id: "canonical-row",
-        text: "canonical",
-        timestamp: new Date("2026-07-27T10:00:00.000Z"),
-      },
-    ];
-
-    useSessionStore.getState().applyAgentTimelineResponseState("test-server", "agent-1", {
-      items,
-      head: [],
-      range: { epoch: "epoch-1", startSeq: 51, endSeq: 100 },
-      older: "available",
-      synchronized: true,
-      acknowledgedClientMessageIds: [],
-    });
-
-    expect(
-      selectAgentTimelineState(useSessionStore.getState().sessions["test-server"], "agent-1"),
-    ).toEqual({
-      status: "synced",
-      items,
-      range: { epoch: "epoch-1", startSeq: 51, endSeq: 100 },
-      older: "available",
-    });
-  });
-
-  it("represents an empty authoritative timeline without inventing a range", () => {
-    initializeTestSession();
-    useSessionStore.getState().applyAgentTimelineResponseState("test-server", "agent-1", {
-      items: [],
-      head: [],
-      range: null,
-      older: "none",
-      synchronized: true,
-      acknowledgedClientMessageIds: [],
-    });
-
-    expect(
-      selectAgentTimelineState(useSessionStore.getState().sessions["test-server"], "agent-1"),
-    ).toEqual({ status: "synced", items: [], range: null, older: "none" });
-  });
-});
-
 describe("normalizeWorkspaceDescriptor", () => {
   it("normalizes workspace scripts and invalid activity timestamps", () => {
     const scripts = [