fix: Autoscroll detection (#23026)

tools/server/webui/src/lib/components/app/chat/ChatScreen/ChatScreen.svelte

@@ -323,7 +323,7 @@
 	});
 
 	function handleMessagesReady() {
-		if (!disableAutoScroll) {
+		if (!disableAutoScroll && !autoScroll.userScrolledUp) {
 			requestAnimationFrame(() => {
 				autoScroll.scrollToBottom('instant');
 			});
@@ -379,7 +379,9 @@
 					messages={activeMessages()}
 					onUserAction={() => {
 						autoScroll.enable();
-						autoScroll.scrollToBottom();
+						if (!autoScroll.userScrolledUp) {
+							autoScroll.scrollToBottom();
+						}
 					}}
 					onMessagesReady={handleMessagesReady}
 				/>

tools/server/webui/src/lib/hooks/use-auto-scroll.svelte.ts

@@ -17,7 +17,6 @@ export class AutoScrollController {
 	private _userScrolledUp = $state(false);
 	private _lastScrollTop = $state(0);
 	private _scrollInterval: ReturnType<typeof setInterval> | undefined;
-	private _scrollTimeout: ReturnType<typeof setTimeout> | undefined;
 	private _container: HTMLElement | undefined;
 	private _disabled: boolean;
 	private _mutationObserver: MutationObserver | null = null;
@@ -51,6 +50,7 @@ export class AutoScrollController {
 	 * Updates the disabled state.
 	 */
 	setDisabled(disabled: boolean): void {
+		if (this._disabled === disabled) return;
 		this._disabled = disabled;
 		if (disabled) {
 			this._autoScrollEnabled = false;
@@ -80,17 +80,6 @@ export class AutoScrollController {
 			this._autoScrollEnabled = true;
 		}
 
-		if (this._scrollTimeout) {
-			clearTimeout(this._scrollTimeout);
-		}
-
-		this._scrollTimeout = setTimeout(() => {
-			if (isAtBottom) {
-				this._userScrolledUp = false;
-				this._autoScrollEnabled = true;
-			}
-		}, AUTO_SCROLL_INTERVAL);
-
 		this._lastScrollTop = scrollTop;
 	}
 
@@ -157,11 +146,6 @@ export class AutoScrollController {
 	destroy(): void {
 		this.stopInterval();
 		this._doStopObserving();
-
-		if (this._scrollTimeout) {
-			clearTimeout(this._scrollTimeout);
-			this._scrollTimeout = undefined;
-		}
 	}
 
 	/**