Fix terminal auto-scroll and jump-to-bottom button coexistence

The previous fix checked isAtBottomRef inside the write callback, but
xterm's own scroll events during write processing could set the ref to
false (viewport desync), breaking auto-follow entirely.

Introduce a separate autoFollowRef that tracks user intent:
- Set to false only by explicit mouse wheel scroll-up (capture phase)
- Set to true when viewport reaches bottom or user clicks the button
- Write callback uses autoFollowRef so desync doesn't kill auto-follow
  but user scroll-up correctly pauses it

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

app/src/components/terminal/TerminalView.tsx

@@ -35,6 +35,10 @@ export default function TerminalView({ sessionId, active }: Props) {
   const [detectedUrl, setDetectedUrl] = useState<string | null>(null);
   const [imagePasteMsg, setImagePasteMsg] = useState<string | null>(null);
   const [isAtBottom, setIsAtBottom] = useState(true);
+  const isAtBottomRef = useRef(true);
+  // Tracks user intent to follow output — only set to false by explicit user
+  // actions (mouse wheel up), not by xterm scroll events during writes.
+  const autoFollowRef = useRef(true);
 
   useEffect(() => {
     if (!containerRef.current) return;
@@ -131,10 +135,32 @@ export default function TerminalView({ sessionId, active }: Props) {
       sendInput(sessionId, data);
     });
 
-    // Track scroll position to show "Jump to Current" button
+    // Detect user-initiated scroll-up (mouse wheel) to pause auto-follow.
+    // Captured during capture phase so it fires before xterm's own handler.
+    const handleWheel = (e: WheelEvent) => {
+      if (e.deltaY < 0) {
+        autoFollowRef.current = false;
+      }
+    };
+    containerRef.current.addEventListener("wheel", handleWheel, { capture: true, passive: true });
+
+    // Track scroll position to show "Jump to Current" button.
+    // Debounce state updates via rAF to avoid excessive re-renders during rapid output.
+    let scrollStateRafId: number | null = null;
     const scrollDisposable = term.onScroll(() => {
       const buf = term.buffer.active;
-      setIsAtBottom(buf.viewportY >= buf.baseY);
+      const atBottom = buf.viewportY >= buf.baseY;
+      isAtBottomRef.current = atBottom;
+      // Re-enable auto-follow when viewport reaches the bottom
+      if (atBottom) {
+        autoFollowRef.current = true;
+      }
+      if (scrollStateRafId === null) {
+        scrollStateRafId = requestAnimationFrame(() => {
+          scrollStateRafId = null;
+          setIsAtBottom(isAtBottomRef.current);
+        });
+      }
     });
 
     // Track text selection to show copy hint in status bar
@@ -187,7 +213,17 @@ export default function TerminalView({ sessionId, active }: Props) {
 
     const outputPromise = onOutput(sessionId, (data) => {
       if (aborted) return;
-      term.write(data);
+      term.write(data, () => {
+        // Keep viewport pinned to bottom when user hasn't scrolled up.
+        // Uses autoFollowRef (user intent) rather than isAtBottomRef (viewport
+        // position) so that xterm desync during writes doesn't kill auto-follow,
+        // but an explicit user scroll-up does pause it.
+        if (autoFollowRef.current) {
+          term.scrollToBottom();
+          isAtBottomRef.current = true;
+          setIsAtBottom(true);
+        }
+      });
       detector.feed(data);
 
       // Scan for SSO refresh marker in terminal output
@@ -229,8 +265,13 @@ export default function TerminalView({ sessionId, active }: Props) {
       resizeRafId = requestAnimationFrame(() => {
         resizeRafId = null;
         if (!containerRef.current || containerRef.current.offsetWidth === 0) return;
+        const wasAtBottom = isAtBottomRef.current;
         fitAddon.fit();
         resize(sessionId, term.cols, term.rows);
+        // Maintain scroll position after resize reflow
+        if (wasAtBottom) {
+          term.scrollToBottom();
+        }
       });
     });
     resizeObserver.observe(containerRef.current);
@@ -246,9 +287,11 @@ export default function TerminalView({ sessionId, active }: Props) {
       scrollDisposable.dispose();
       selectionDisposable.dispose();
       setTerminalHasSelection(false);
+      containerRef.current?.removeEventListener("wheel", handleWheel, { capture: true });
       containerRef.current?.removeEventListener("paste", handlePaste, { capture: true });
       outputPromise.then((fn) => fn?.());
       exitPromise.then((fn) => fn?.());
+      if (scrollStateRafId !== null) cancelAnimationFrame(scrollStateRafId);
       if (resizeRafId !== null) cancelAnimationFrame(resizeRafId);
       resizeObserver.disconnect();
       try { webglRef.current?.dispose(); } catch { /* may already be disposed */ }
@@ -314,8 +357,15 @@ export default function TerminalView({ sessionId, active }: Props) {
   }, [detectedUrl]);
 
   const handleScrollToBottom = useCallback(() => {
-    termRef.current?.scrollToBottom();
-    setIsAtBottom(true);
+    const term = termRef.current;
+    if (term) {
+      autoFollowRef.current = true;
+      // Re-fit first to fix viewport desync (same thing a resize does)
+      fitRef.current?.fit();
+      term.scrollToBottom();
+      isAtBottomRef.current = true;
+      setIsAtBottom(true);
+    }
   }, []);
 
   return (