fix(chat): complete initial placement immediately after history refresh settles (#3918)

apps/web/components/task/chat/message-list-native-scroll.ts

@@ -1543,6 +1543,21 @@ type InitialScrollPositionEffectParams = Omit<InitialScrollPositionParams, "plac
   activationPendingRef: React.RefObject<boolean>;
 };
 
+function handleEmptyTranscriptPlacement(params: {
+  hasEmptyTranscript: boolean;
+  envSwitchPlacementToken: number | null;
+  historyRefreshPending: boolean;
+  didInitialScroll: React.RefObject<boolean>;
+  activationPendingRef: React.RefObject<boolean>;
+}): boolean {
+  if (!params.hasEmptyTranscript) return false;
+  if (params.envSwitchPlacementToken !== null && !params.historyRefreshPending) {
+    markInitialScrollConsumed(params.didInitialScroll, params.activationPendingRef);
+    completeEnvSwitchPlacement(params.envSwitchPlacementToken);
+  }
+  return true;
+}
+
 function runInitialScrollPositionEffect(
   params: InitialScrollPositionEffectParams,
 ): void | (() => void) {
@@ -1565,13 +1580,13 @@ function runInitialScrollPositionEffect(
     activationPendingRef,
   } = params;
   if (!isVisible || (envSwitchPlacementToken !== null && isRestoringLayout)) return;
-  const hasEmptyTranscript = itemCount === 0;
-  if (envSwitchPlacementToken !== null && hasEmptyTranscript) {
-    if (historyRefreshPending) return;
-    markInitialScrollConsumed(didInitialScroll, activationPendingRef);
-    completeEnvSwitchPlacement(envSwitchPlacementToken);
-    return;
-  }
+  const hasEmptyTranscript = handleEmptyTranscriptPlacement({
+    hasEmptyTranscript: itemCount === 0,
+    envSwitchPlacementToken,
+    historyRefreshPending,
+    didInitialScroll,
+    activationPendingRef,
+  });
   if (didInitialScroll.current || hasEmptyTranscript) return;
   const element = scrollRef.current;
   if (!element) return;
@@ -1605,7 +1620,11 @@ function runInitialScrollPositionEffect(
     if (phase === "provisional") provisionalTokenRef.current = envSwitchPlacementToken;
   };
 
-  if (activationPendingRef.current) return scheduleAfterPanelRestore(applyInitialScroll);
+  const isEnvSwitchSettling =
+    envSwitchPlacementToken !== null && provisionalTokenRef.current === envSwitchPlacementToken;
+  if (activationPendingRef.current && !isEnvSwitchSettling) {
+    return scheduleAfterPanelRestore(applyInitialScroll);
+  }
   applyInitialScroll();
 }
 

apps/web/components/task/chat/message-list-native.test.tsx

@@ -86,6 +86,7 @@ const HARNESS_RENDER_ERROR = "harness did not render";
 const NATIVE_SCROLL_MANAGEMENT_TEST_ID = "native-scroll-management-container";
 const AUTO_SCROLL_CONTAINER_TEST_ID = "auto-scroll-container";
 const CACHED_MESSAGE_ID = "cached-message";
+const SETTLED_MESSAGE_ID = "settled-message";
 const TEST_MESSAGES = [{} as Message];
 /** Always returns false: the harness never locks programmatic scrolling. */
 const NEVER_LOCKED = () => false;
@@ -412,18 +413,18 @@ describe("useNativeScrollManagement transcript pagination", () => {
       metrics.scrollHeight = 1400;
       rerender(
         <NativeScrollManagementHarness
-          items={[transcriptMessage("settled-message")]}
+          items={[transcriptMessage(SETTLED_MESSAGE_ID)]}
           metrics={metrics}
           sessionId="session-b"
           enabled
         />,
       );
-      act(() => {
-        for (let frame = frames.shift(); frame; frame = frames.shift()) frame(0);
-      });
 
       expect(scrollContainer.scrollTop).toBe(1400);
       expect(mockDockviewState.pendingChatInitialPlacement).toBeNull();
+      act(() => {
+        for (let frame = frames.shift(); frame; frame = frames.shift()) frame(0);
+      });
     } finally {
       vi.unstubAllGlobals();
     }
@@ -476,17 +477,17 @@ describe("useNativeScrollManagement transcript pagination", () => {
       metrics.scrollTop = 915;
       rerender(
         <NativeScrollManagementHarness
-          items={[transcriptMessage("settled-message")]}
+          items={[transcriptMessage(SETTLED_MESSAGE_ID)]}
           metrics={metrics}
           sessionId="session-b"
         />,
       );
-      act(() => {
-        for (let frame = frames.shift(); frame; frame = frames.shift()) frame(0);
-      });
 
       expect(scrollContainer.scrollTop).toBe(320);
       expect(scrollContainer.scrollTop).not.toBe(810);
+      act(() => {
+        for (let frame = frames.shift(); frame; frame = frames.shift()) frame(0);
+      });
     } finally {
       vi.unstubAllGlobals();
     }
@@ -556,19 +557,19 @@ describe("useNativeScrollManagement transcript pagination", () => {
       metrics.scrollTop = 480;
       rerender(
         <NativeScrollManagementHarness
-          items={[transcriptMessage("settled-message")]}
+          items={[transcriptMessage(SETTLED_MESSAGE_ID)]}
           metrics={metrics}
           sessionId="session-b"
           enabled
           hasUnreadDivider
         />,
       );
-      act(() => {
-        for (let frame = frames.shift(); frame; frame = frames.shift()) frame(0);
-      });
 
       expect(metrics.scrollTop).toBe(480);
       expect(mockDockviewState.pendingChatInitialPlacement).toBeNull();
+      act(() => {
+        for (let frame = frames.shift(); frame; frame = frames.shift()) frame(0);
+      });
     } finally {
       vi.unstubAllGlobals();
     }