buddy scroll

src/components/shell/AssistantPanel.tsx

@@ -350,6 +350,7 @@ export function AssistantPanel({
   const [isFocused, setIsFocused] = useState(false);
   const [isExpanded, setIsExpanded] = useState(false);
   const textareaRef = useRef<HTMLTextAreaElement>(null);
+  const threadRef = useRef<HTMLDivElement>(null);
   const { width, setWidth, reset } = useAssistantWidth();
   const [isDragging, setDragging] = useState(false);
 
@@ -405,6 +406,30 @@ export function AssistantPanel({
     setThread([]);
   }, [key]);
 
+  /*
+   * Follow the conversation down, unless the person has scrolled away from it.
+   *
+   * A chat that does not follow leaves the newest answer below the fold, which
+   * reads as nothing having happened. One that follows unconditionally yanks
+   * somebody out of an earlier answer they were still reading the moment a
+   * reply lands — and a reply can land a while after the question, because a
+   * tool call and a model round trip are seconds, not milliseconds.
+   *
+   * So: only when they were already at the bottom. The 40px allowance covers
+   * fractional scroll heights, which browsers disagree about by a pixel or two
+   * at non-integer zoom levels — without it this silently stops following for
+   * anybody not at 100%.
+   */
+  useEffect(() => {
+    const el = threadRef.current;
+    if (!el) return;
+
+    const distanceFromBottom = el.scrollHeight - el.scrollTop - el.clientHeight;
+    if (distanceFromBottom > 40) return;
+
+    el.scrollTo({ top: el.scrollHeight, behavior: 'smooth' });
+  }, [thread]);
+
   /*
    * Approving is its own call, with no question in it.
    *
@@ -569,6 +594,35 @@ export function AssistantPanel({
           )}
         </div>
 
+        {/*
+          The scrolling part, and the only one.
+
+          Everything above this is chrome that stays put; everything below it is
+          the composer, which must never leave the screen. Before this existed
+          the panel was one `height: 100%` column with no overflow anywhere: a
+          thread longer than the panel pushed the chips and the composer past
+          the bottom edge, and there was nothing to scroll — the box you type
+          into simply left the screen and the conversation could not be read
+          back.
+
+          `minHeight: 0` is the load-bearing half. A flex child defaults to
+          `min-height: auto`, which means it refuses to shrink below its content,
+          so `flex: 1` alone would let this grow to the height of the whole
+          conversation and overflow the panel exactly as before — the scrollbar
+          never appears and nothing looks wrong in the code.
+        */}
+        <div
+          ref={threadRef}
+          style={{
+            flex: 1,
+            minHeight: 0,
+            overflowY: 'auto',
+            overscrollBehavior: 'contain',
+            display: 'flex',
+            flexDirection: 'column',
+            gap: 16,
+          }}
+        >
         {/* Greeting — top-aligned, because it is the first thing in a
             conversation, not a splash screen. */}
         <div>
@@ -608,9 +662,9 @@ export function AssistantPanel({
           </p>
         </div>
 
-        {/* The conversation. Above the spacer, so a short thread sits under the
-            greeting and a long one pushes the chips and composer down rather
-            than scrolling away from them. */}
+        {/* The conversation. Inside the scroller with the greeting above it, so
+            a short thread reads straight on from the greeting and a long one
+            scrolls under it — with the chips and the composer staying put. */}
         {thread.length > 0 ? (
           <div
             role="log"
@@ -629,8 +683,7 @@ export function AssistantPanel({
             ))}
           </div>
         ) : null}
-
-        <div style={{ flex: 1 }} />
+        </div>
 
         {/* Chips wrap, never scroll — a half-visible button at a scroller's edge
             is a bug no amount of fade masking fixes. */}