From 378f11d6dcecc8b27ac66b9117051207f4cf039f Mon Sep 17 00:00:00 2001
From: Mathias Fredriksson <mafredri@gmail.com>
Date: Mon, 30 Mar 2026 15:36:42 +0300
Subject: [PATCH] fix(site/src/pages/AgentsPage): fix scroll-to-bottom pin
 starvation in agents chat (#23778)

scheduleBottomPin() cancelled any in-flight pin and restarted the
double-RAF chain on every ResizeObserver notification. When content
height changes on consecutive frames (e.g. during streaming where
SmoothText reveals characters each frame and markdown re-rendering
occasionally changes block height), the inner RAF that actually sets
scrollTop is perpetually cancelled before it fires. The scroll falls
behind the growing content.

Two fixes:

1. Make scheduleBottomPin() idempotent: if a pin is already in-flight,
   skip. The inner RAF reads scrollHeight at execution time so it
   always targets the latest bottom. User-interrupt paths (wheel,
   touch) still cancel via cancelPendingPins().

2. Add overscroll-behavior:contain to the scroll container. Prevents
   elastic overscroll from generating extra scroll events that could
   flip autoScrollRef to false.
---
 site/src/pages/AgentsPage/AgentChatPageView.tsx | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/site/src/pages/AgentsPage/AgentChatPageView.tsx b/site/src/pages/AgentsPage/AgentChatPageView.tsx
index fa22354f01..a739069a93 100644
--- a/site/src/pages/AgentsPage/AgentChatPageView.tsx
+++ b/site/src/pages/AgentsPage/AgentChatPageView.tsx
@@ -792,7 +792,16 @@ const ScrollAnchoredContainer: FC<{
 		};
 
 		const scheduleBottomPin = () => {
-			cancelPendingPins();
+			// If a pin is already in-flight, let it complete. The
+			// inner RAF reads scrollHeight at execution time so it
+			// always targets the latest bottom. Cancelling and
+			// rescheduling on every ResizeObserver notification
+			// starves the pin on Safari, where sticky-element
+			// repositioning generates extra resize events that
+			// perpetually restart the double-RAF chain.
+			if (pinOuterRafId !== null || pinInnerRafId !== null) {
+				return;
+			}
 			pendingWheelPinRef.current = false;
 			isRestoringScrollRef.current = true;
 			// Double-RAF lets React's commit phase and the browser's
@@ -1149,7 +1158,7 @@ const ScrollAnchoredContainer: FC<{
 			<div
 				ref={scrollContainerRef}
 				data-testid="scroll-container"
-				className="flex min-h-0 flex-1 flex-col overflow-y-auto [overflow-anchor:none] [scrollbar-gutter:stable] [scrollbar-width:thin] [scrollbar-color:hsl(var(--surface-quaternary))_transparent]"
+				className="flex min-h-0 flex-1 flex-col overflow-y-auto [overflow-anchor:none] [overscroll-behavior:contain] [scrollbar-gutter:stable] [scrollbar-width:thin] [scrollbar-color:hsl(var(--surface-quaternary))_transparent]"
 			>
 				<div ref={contentRef}>
 					{hasMoreMessages && (