fix: cancel chat scrolls on reconnect

ui/src/pages/chat/chat-pane-context.ts

@@ -37,6 +37,7 @@ import {
   reconcileStaleChatRunAfterSessionStatePublication,
   replayPendingChatAbort,
 } from "./run-lifecycle.ts";
+import { cancelChatScroll } from "./scroll.ts";
 import { clearChatMessagesFromCache } from "./session-message-cache.ts";
 import { normalizeSidebarLayout } from "./sidebar-layout.ts";
 import { reconcileWaitingApprovalsFromSnapshot } from "./tool-stream.ts";
@@ -184,6 +185,7 @@ export abstract class ChatPaneContext extends ChatPaneLifecycle {
     }
     if (sourceChanged) {
       this.cancelHeaderRename();
+      cancelChatScroll(state);
       releaseChatMediaResourceSubscriber(state.requestUpdate);
       // A reconnect can retain the browser client. Keep async ownership tied
       // to the logical connection, not only the transport object identity.

ui/src/pages/chat/chat-pane-lifecycle.test.ts

@@ -899,6 +899,27 @@ describe("chat pane connection lifecycle", () => {
     expect(state.chatLoading).toBe(true);
   });
 
+  it("cancels scroll work owned by the prior Gateway connection", () => {
+    const client = { request: vi.fn() } as unknown as GatewayBrowserClient;
+    const { pane, state } = createTestChatPane({ client, sessions: {} as SessionCapability });
+    const cancelCommit = vi.fn();
+    const initialScrollGeneration = state.chatScrollGeneration;
+    state.chatScrollCommitCleanup = cancelCommit;
+    state.chatIsProgrammaticScroll = true;
+
+    pane.applyGatewaySnapshot({
+      ...pane.context.gateway.snapshot,
+      client,
+      phase: "reconnecting",
+      hello: null,
+    });
+
+    expect(cancelCommit).toHaveBeenCalledOnce();
+    expect(state.chatScrollCommitCleanup).toBeNull();
+    expect(state.chatScrollGeneration).toBe(initialScrollGeneration + 1);
+    expect(state.chatIsProgrammaticScroll).toBe(false);
+  });
+
   it("refreshes the transcript before secondary hydration after a same-client reconnect", () => {
     const request = vi.fn(() => new Promise<never>(() => {}));
     const client = {