tui: stabilize transcript scrollback

src/tui/components/chat-log.ts

@@ -50,11 +50,16 @@ export class ChatLog extends Container {
 
   private append(component: Component) {
     const wasAtLatest = this.scrollOffset === 0;
+    const previousLineCount = wasAtLatest ? 0 : this.getRenderedLineCount(this.lastRenderWidth);
     this.addChild(component);
     this.pruneOverflow();
     if (wasAtLatest) {
       this.scrollToLatest();
+      return;
     }
+    const nextLineCount = this.getRenderedLineCount(this.lastRenderWidth);
+    this.scrollOffset += Math.max(0, nextLineCount - previousLineCount);
+    this.clampScrollOffset();
   }
 
   setViewportHeight(height: number | null) {
@@ -109,6 +114,7 @@ export class ChatLog extends Container {
     this.toolById.clear();
     this.streamingRuns.clear();
     this.btwMessage = null;
+    this.scrollToLatest();
   }
 
   addSystem(text: string) {

src/tui/tui.ts

@@ -230,6 +230,10 @@ export function resolveInitialTuiAgentId(params: {
   return normalizeAgentId(params.fallbackAgentId);
 }
 
+function isMouseSgrSequence(data: string): boolean {
+  return /^\x1b\[<\d+;\d+;\d+[Mm]$/.test(data);
+}
+
 export function parseMouseWheelEvent(data: string): { direction: "up" | "down"; row: number; col: number } | null {
   const match = /^\x1b\[<(\d+);(\d+);(\d+)([Mm])$/.exec(data);
   if (!match) {
@@ -552,12 +556,15 @@ export async function runTui(opts: TuiOptions) {
   const tui = new TUI(new ProcessTerminal());
   const dedupeBackspace = createBackspaceDeduper();
   tui.addInputListener((data) => {
-    const mouse = parseMouseWheelEvent(data);
-    if (!mouse || tui.hasOverlay()) {
+    if (!isMouseSgrSequence(data)) {
       return undefined;
     }
+    const mouse = parseMouseWheelEvent(data);
+    if (!mouse || tui.hasOverlay()) {
+      return { consume: true };
+    }
     if (mouse.row < chatViewportTop || mouse.row > chatViewportBottom) {
-      return undefined;
+      return { consume: true };
     }
     if (mouse.direction === "up") {
       chatLog.scrollLines(3);