fix(chat): defer scroller resize correction off the ResizeObserver callback

src/components/ui/message-scroller-primitive/use-message-scroller-controller.ts

@@ -68,6 +68,7 @@ function useMessageScrollerController({
 		modeRef,
 		prependRestoreRef,
 		preserveScrollOnPrependRef,
+		resizeFrameRef,
 		rootRef,
 		scrollEdgeThresholdRef,
 		spacerGapRef,
@@ -370,20 +371,40 @@ function useMessageScrollerController({
 	]);
 
 	const handleResize = React.useCallback(() => {
-		if (modeRef.current === "following-bottom" && autoScrollRef.current) {
-			scrollToEnd({ behavior: "auto" });
+		// Defer the scroll correction out of the ResizeObserver callback. Writing
+		// scrollTop synchronously here mutates layout inside the same delivery, which
+		// the browser reports as "ResizeObserver loop completed with undelivered
+		// notifications" — benign, but it fires on every frame of a streaming reply.
+		// Coalesce bursts of resize notifications onto a single frame.
+		if (resizeFrameRef.current !== null) {
 			return;
 		}
 
-		// Hold the anchored turn in place as content below it resizes (a reply
-		// streaming in, or a transient marker collapsing) — otherwise the shrinking
-		// content lets the browser clamp scrollTop and the turn drops.
-		if (reanchorToAnchoredMessage()) {
-			return;
-		}
+		resizeFrameRef.current = window.requestAnimationFrame(() => {
+			resizeFrameRef.current = null;
 
-		scheduleStateCommit();
-	}, [autoScrollRef, modeRef, reanchorToAnchoredMessage, scheduleStateCommit, scrollToEnd]);
+			if (modeRef.current === "following-bottom" && autoScrollRef.current) {
+				scrollToEnd({ behavior: "auto" });
+				return;
+			}
+
+			// Hold the anchored turn in place as content below it resizes (a reply
+			// streaming in, or a transient marker collapsing) — otherwise the shrinking
+			// content lets the browser clamp scrollTop and the turn drops.
+			if (reanchorToAnchoredMessage()) {
+				return;
+			}
+
+			scheduleStateCommit();
+		});
+	}, [
+		autoScrollRef,
+		modeRef,
+		reanchorToAnchoredMessage,
+		resizeFrameRef,
+		scheduleStateCommit,
+		scrollToEnd,
+	]);
 
 	const userScrollIntent = React.useCallback(() => {
 		if (
@@ -487,12 +508,17 @@ function useMessageScrollerController({
 				stateFrameRef.current = null;
 			}
 
+			if (resizeFrameRef.current !== null) {
+				window.cancelAnimationFrame(resizeFrameRef.current);
+				resizeFrameRef.current = null;
+			}
+
 			if (autoscrollingTimeoutRef.current !== null) {
 				window.clearTimeout(autoscrollingTimeoutRef.current);
 				autoscrollingTimeoutRef.current = null;
 			}
 		};
-	}, [autoscrollingTimeoutRef, stateFrameRef]);
+	}, [autoscrollingTimeoutRef, resizeFrameRef, stateFrameRef]);
 
 	React.useLayoutEffect(() => {
 		if (autoScroll && modeRef.current === "following-bottom" && itemCountRef.current > 0) {

src/components/ui/message-scroller-primitive/use-message-scroller-refs.ts

@@ -27,6 +27,7 @@ type MessageScrollerRefs = {
 		viewportTop: number;
 	} | null>;
 	preserveScrollOnPrependRef: React.RefObject<boolean>;
+	resizeFrameRef: React.RefObject<number | null>;
 	rootRef: React.RefObject<HTMLDivElement | null>;
 	scrollEdgeThresholdRef: React.RefObject<number>;
 	scrollMarginRef: React.RefObject<number>;
@@ -73,6 +74,10 @@ function useMessageScrollerRefs({
 	} | null>(null);
 	const scrollPreviousItemPeekRef = React.useRef(scrollPreviousItemPeek);
 	const preserveScrollOnPrependRef = React.useRef(true);
+	// Coalesces ResizeObserver-driven scroll corrections onto a frame so the
+	// scrollTop write lands outside the observer callback (avoids the benign
+	// "ResizeObserver loop" warning that layout-in-callback triggers).
+	const resizeFrameRef = React.useRef<number | null>(null);
 	const rootRef = React.useRef<HTMLDivElement | null>(null);
 	const scrollMarginRef = React.useRef(scrollMargin);
 	const spacerGapRef = React.useRef(0);
@@ -106,6 +111,7 @@ function useMessageScrollerRefs({
 		modeRef,
 		prependRestoreRef,
 		preserveScrollOnPrependRef,
+		resizeFrameRef,
 		rootRef,
 		scrollEdgeThresholdRef,
 		scrollMarginRef,

src/integrations/posthog/provider.tsx

@@ -77,6 +77,22 @@ export function capturePostHogClientException(error: Error, properties?: Record<
 	posthog.captureException(error, properties);
 }
 
+// Chromium surfaces these as global "error" events with no real Error attached.
+// They are benign layout-timing warnings, not exceptions worth tracking, and a
+// single chat session can emit hundreds of them — enough to bury real errors.
+const BENIGN_BROWSER_ERROR_PATTERNS = [
+	"ResizeObserver loop completed with undelivered notifications",
+	"ResizeObserver loop limit exceeded",
+];
+
+function isBenignBrowserError(message: string | undefined) {
+	if (!message) {
+		return false;
+	}
+
+	return BENIGN_BROWSER_ERROR_PATTERNS.some((pattern) => message.includes(pattern));
+}
+
 function normalizeBrowserError(value: unknown, fallbackMessage: string) {
 	if (value instanceof Error) {
 		return value;
@@ -140,6 +156,10 @@ function PostHogAuthSync() {
 function PostHogGlobalErrorCapture() {
 	useEffect(() => {
 		const handleError = (event: ErrorEvent) => {
+			if (isBenignBrowserError(event.message)) {
+				return;
+			}
+
 			capturePostHogClientException(
 				normalizeBrowserError(event.error ?? event.message, "Unhandled browser error"),
 				{