Load complete chat history when reaching the top (#2481)

* fix(chat): load older timeline history consistently

Pagination depended on scroll events, so short or compacted initial pages could never request older history. Reevaluate edge visibility as layout and history change, and standardize loading indicators on the canonical app spinner.

* fix(chat): keep older history loading reliably

Use authoritative timeline cursor progress so merged rows cannot stall pagination. Wait for bottom anchoring before evaluating the history edge, and re-arm retries on a fresh upward gesture without automatic failure loops.

packages/app/src/agent-stream/strategy-web.test.tsx

@@ -133,6 +133,7 @@ describe("createWebStreamStrategy", () => {
             onNearHistoryStart: vi.fn(),
             isLoadingOlderHistory: false,
             hasOlderHistory: false,
+            olderHistoryProgressKey: null,
             scrollEnabled: true,
             listStyle: null,
             baseListContentContainerStyle: null,
@@ -176,6 +177,7 @@ describe("createWebStreamStrategy", () => {
       onNearHistoryStart: vi.fn(),
       isLoadingOlderHistory: false,
       hasOlderHistory: false,
+      olderHistoryProgressKey: null,
       scrollEnabled: true,
       listStyle: null,
       baseListContentContainerStyle: null,
@@ -231,6 +233,7 @@ describe("createWebStreamStrategy", () => {
           onNearHistoryStart: vi.fn(),
           isLoadingOlderHistory: false,
           hasOlderHistory: false,
+          olderHistoryProgressKey: null,
           scrollEnabled: true,
           listStyle: null,
           baseListContentContainerStyle: null,
@@ -314,6 +317,7 @@ describe("createWebStreamStrategy", () => {
             onNearHistoryStart,
             isLoadingOlderHistory: false,
             hasOlderHistory: true,
+            olderHistoryProgressKey: "epoch-1:20",
             scrollEnabled: true,
             listStyle: null,
             baseListContentContainerStyle: null,
@@ -323,10 +327,6 @@ describe("createWebStreamStrategy", () => {
       );
     });
 
-    await act(async () => {
-      await new Promise((resolve) => requestAnimationFrame(resolve));
-    });
-
     const scrollContainer = container.querySelector('[data-testid="agent-chat-scroll"]');
     if (!(scrollContainer instanceof HTMLElement)) {
       throw new Error("Expected agent chat scroll container");
@@ -335,11 +335,109 @@ describe("createWebStreamStrategy", () => {
     Object.defineProperty(scrollContainer, "scrollHeight", { configurable: true, value: 1200 });
     Object.defineProperty(scrollContainer, "scrollTop", { configurable: true, value: 64 });
 
+    await act(async () => {
+      await new Promise((resolve) => requestAnimationFrame(resolve));
+    });
+
+    expect(onNearHistoryStart).not.toHaveBeenCalled();
+
     act(() => {
+      scrollContainer.dispatchEvent(new WheelEvent("wheel", { deltaY: -1 }));
       scrollContainer?.dispatchEvent(new Event("scroll"));
     });
 
     expect(onNearHistoryStart).toHaveBeenCalledTimes(1);
+
+    act(() => {
+      scrollContainer.dispatchEvent(new WheelEvent("wheel", { deltaY: -1 }));
+    });
+
+    expect(onNearHistoryStart).toHaveBeenCalledTimes(2);
+  });
+
+  it("waits for bottom anchoring before evaluating a delayed initial tail", async () => {
+    HTMLElement.prototype.scrollTo = vi.fn(function (
+      this: HTMLElement,
+      options?: ScrollToOptions | number,
+      y?: number,
+    ) {
+      const top = typeof options === "object" ? (options.top ?? 0) : (y ?? 0);
+      Object.defineProperty(this, "scrollTop", { configurable: true, value: top });
+    });
+    const strategy = createWebStreamStrategy({ isMobileBreakpoint: true });
+    const viewportRef = React.createRef<StreamViewportHandle>();
+    const onNearHistoryStart = vi.fn();
+    const renderInput = {
+      agentId: "agent",
+      boundary: {
+        hasVirtualizedHistory: false,
+        hasMountedHistory: false,
+        hasLiveHead: false,
+      },
+      renderers: createRenderers(vi.fn()),
+      listEmptyComponent: null,
+      viewportRef,
+      routeBottomAnchorRequest: null,
+      isAuthoritativeHistoryReady: true,
+      onNearBottomChange: vi.fn(),
+      onNearHistoryStart,
+      isLoadingOlderHistory: false,
+      hasOlderHistory: false,
+      olderHistoryProgressKey: null,
+      scrollEnabled: true,
+      listStyle: null,
+      baseListContentContainerStyle: null,
+      forwardListContentContainerStyle: null,
+    };
+    container = document.createElement("div");
+    document.body.appendChild(container);
+    root = createRoot(container);
+
+    act(() => {
+      root?.render(
+        strategy.render({
+          ...renderInput,
+          segments: { historyVirtualized: [], historyMounted: [], liveHead: [] },
+        }),
+      );
+    });
+    await act(async () => {
+      await new Promise((resolve) => requestAnimationFrame(resolve));
+    });
+
+    const scrollContainer = container.querySelector('[data-testid="agent-chat-scroll"]');
+    if (!(scrollContainer instanceof HTMLElement)) {
+      throw new Error("Expected agent chat scroll container");
+    }
+    Object.defineProperty(scrollContainer, "clientHeight", { configurable: true, value: 400 });
+    Object.defineProperty(scrollContainer, "scrollHeight", { configurable: true, value: 1200 });
+    Object.defineProperty(scrollContainer, "scrollTop", { configurable: true, value: 0 });
+
+    act(() => {
+      root?.render(
+        strategy.render({
+          ...renderInput,
+          segments: {
+            historyVirtualized: [],
+            historyMounted: [userMessage(1), userMessage(2)],
+            liveHead: [],
+          },
+          boundary: {
+            hasVirtualizedHistory: false,
+            hasMountedHistory: true,
+            hasLiveHead: false,
+          },
+          hasOlderHistory: true,
+          olderHistoryProgressKey: "epoch-1:20",
+        }),
+      );
+    });
+
+    expect(onNearHistoryStart).not.toHaveBeenCalled();
+    await act(async () => {
+      await new Promise((resolve) => requestAnimationFrame(resolve));
+    });
+    expect(onNearHistoryStart).not.toHaveBeenCalled();
   });
 
   it("keeps initial route entry anchored when delayed route readiness arrives before user scroll", async () => {
@@ -378,6 +476,7 @@ describe("createWebStreamStrategy", () => {
       onNearHistoryStart: vi.fn(),
       isLoadingOlderHistory: false,
       hasOlderHistory: false,
+      olderHistoryProgressKey: null,
       scrollEnabled: true,
       listStyle: null,
       baseListContentContainerStyle: null,
@@ -485,6 +584,7 @@ describe("createWebStreamStrategy", () => {
       onNearHistoryStart: vi.fn(),
       isLoadingOlderHistory: false,
       hasOlderHistory: false,
+      olderHistoryProgressKey: null,
       scrollEnabled: true,
       listStyle: null,
       baseListContentContainerStyle: null,
@@ -581,6 +681,7 @@ describe("createWebStreamStrategy", () => {
       onNearHistoryStart: vi.fn(),
       isLoadingOlderHistory: false,
       hasOlderHistory: false,
+      olderHistoryProgressKey: null,
       scrollEnabled: true,
       listStyle: null,
       baseListContentContainerStyle: null,
@@ -679,6 +780,7 @@ describe("createWebStreamStrategy", () => {
       onNearHistoryStart: vi.fn(),
       isLoadingOlderHistory: false,
       hasOlderHistory: false,
+      olderHistoryProgressKey: null,
       scrollEnabled: true,
       listStyle: null,
       baseListContentContainerStyle: null,