web: transcript improvements

web/src/App.tsx

@@ -98,12 +98,25 @@ const EMPTY_MODEL_PREFERENCES: ProviderModelPreferences = {
   xai: null,
 };
 
+const TRANSCRIPT_BOTTOM_GAP = 20;
+const REPLY_SCROLL_BUFFER_MIN = 288;
+const REPLY_SCROLL_BUFFER_MAX = 576;
+const REPLY_SCROLL_BUFFER_VIEWPORT_RATIO = 0.52;
+
 function getModelOptions(catalog: ModelCatalogResponse["providers"], provider: Provider) {
   const providerModels = catalog[provider]?.models ?? [];
   if (providerModels.length) return providerModels;
   return PROVIDER_FALLBACK_MODELS[provider];
 }
 
+function getReplyScrollBufferHeight() {
+  if (typeof window === "undefined") return REPLY_SCROLL_BUFFER_MIN;
+  return Math.min(
+    REPLY_SCROLL_BUFFER_MAX,
+    Math.max(REPLY_SCROLL_BUFFER_MIN, Math.round(window.innerHeight * REPLY_SCROLL_BUFFER_VIEWPORT_RATIO))
+  );
+}
+
 function loadStoredModelPreferences() {
   if (typeof window === "undefined") return EMPTY_MODEL_PREFERENCES;
   try {
@@ -443,6 +456,7 @@ export default function App() {
     return stored.openai ?? PROVIDER_FALLBACK_MODELS.openai[0];
   });
   const [error, setError] = useState<string | null>(null);
+  const [transcriptTailSpacerHeight, setTranscriptTailSpacerHeight] = useState(TRANSCRIPT_BOTTOM_GAP);
   const transcriptContainerRef = useRef<HTMLDivElement>(null);
   const transcriptEndRef = useRef<HTMLDivElement>(null);
   const contextMenuRef = useRef<HTMLDivElement>(null);
@@ -453,12 +467,41 @@ export default function App() {
   const shouldAutoScrollRef = useRef(true);
   const wasSendingRef = useRef(false);
   const pendingReplyScrollRef = useRef(false);
+  const transcriptTailSpacerHeightRef = useRef(TRANSCRIPT_BOTTOM_GAP);
   const [contextMenu, setContextMenu] = useState<ContextMenuState | null>(null);
   const [isMobileSidebarOpen, setIsMobileSidebarOpen] = useState(false);
   const [sidebarQuery, setSidebarQuery] = useState("");
   const initialRouteSelectionRef = useRef<SidebarSelection | null>(readSidebarSelectionFromUrl());
   const hasSyncedSelectionHistoryRef = useRef(false);
 
+  const setTranscriptTailSpacer = (height: number) => {
+    const nextHeight = Math.max(TRANSCRIPT_BOTTOM_GAP, Math.ceil(height));
+    transcriptTailSpacerHeightRef.current = nextHeight;
+    setTranscriptTailSpacerHeight(nextHeight);
+  };
+
+  const expandTranscriptTailSpacer = (height: number) => {
+    const targetHeight = Math.max(TRANSCRIPT_BOTTOM_GAP, Math.ceil(height));
+    setTranscriptTailSpacerHeight((currentHeight) => {
+      const nextHeight = Math.max(currentHeight, targetHeight);
+      transcriptTailSpacerHeightRef.current = nextHeight;
+      return nextHeight;
+    });
+  };
+
+  const settleTranscriptTailSpacer = () => {
+    const container = transcriptContainerRef.current;
+    const currentSpacerHeight = transcriptTailSpacerHeightRef.current;
+    if (!container) {
+      setTranscriptTailSpacer(TRANSCRIPT_BOTTOM_GAP);
+      return;
+    }
+
+    const scrollHeightWithoutSpacer = container.scrollHeight - currentSpacerHeight;
+    const requiredSpacerHeight = container.scrollTop + container.clientHeight - scrollHeightWithoutSpacer;
+    setTranscriptTailSpacer(requiredSpacerHeight);
+  };
+
   const focusComposer = () => {
     if (typeof window === "undefined") return;
     window.requestAnimationFrame(() => {
@@ -653,6 +696,9 @@ export default function App() {
 
   useEffect(() => {
     shouldAutoScrollRef.current = true;
+    if (!isSending || !isChatReplyStreamingInView) {
+      setTranscriptTailSpacer(TRANSCRIPT_BOTTOM_GAP);
+    }
   }, [draftKind, selectedItem?.kind, selectedKey]);
 
   useEffect(() => {
@@ -855,6 +901,7 @@ export default function App() {
 
   const handleSendChat = async (content: string) => {
     pendingReplyScrollRef.current = true;
+    expandTranscriptTailSpacer(getReplyScrollBufferHeight());
 
     const optimisticUserMessage: Message = {
       id: `temp-user-${Date.now()}`,
@@ -1043,6 +1090,7 @@ export default function App() {
     if (currentSelection?.kind === "chat" && currentSelection.id === chatId) {
       await refreshChat(chatId);
     }
+    settleTranscriptTailSpacer();
     setPendingChatState(null);
   };
 
@@ -1462,9 +1510,11 @@ export default function App() {
                 onStartChat={selectedSearch ? handleStartChatFromSearch : undefined}
               />
             )}
-            {isChatReplyStreamingInView ? (
-              <div className="mx-auto mt-6 h-[52vh] min-h-72 max-h-[36rem] max-w-4xl" aria-hidden="true" />
-            ) : null}
+            <div
+              className="mx-auto max-w-4xl"
+              style={{ height: `${transcriptTailSpacerHeight}px` }}
+              aria-hidden="true"
+            />
             <div ref={transcriptEndRef} />
           </div>