fix(twinki): avoid full redraw for off-screen animation ticks (#1433)

* local

* fix(twinki): avoid full redraw for off-screen animation ticks

- Skip static output accumulation/prepend in alt screen (no scrollback)
- Replace full CLEAR_ALL redraw with viewport-only re-scan when content
  didn't shrink and changes are above the viewport. This prevents
  flashing and scrollback wipe from spinner/thinking animations that
  scroll past the viewport during long streaming responses.
- Shrink case still falls through to full redraw (stale rows need clearing)

---------

Co-authored-by: Kenneth S. <kennvene@amazon.com>

Author: kensave

packages/tui/src/components/ui/CommandMenu.tsx

@@ -75,16 +75,19 @@ export const CommandMenu: React.FC = () => {
     return match?.[1] ?? '';
   }, [commandInputValue, activeTrigger]);
 
-  // Search files when query changes
+  // Debounce file search so rapid keystrokes (e.g. typing @kennvene) don't
+  // trigger a synchronous readdirSync walk on every character.
   useEffect(() => {
     if (activeTrigger?.key === '@' && fileQuery) {
-      const results = searchFiles(fileQuery);
-      setFileResults(results);
-      setFilePickerHasResults(results.length > 0);
-    } else {
-      setFileResults([]);
-      setFilePickerHasResults(false);
+      const timer = setTimeout(() => {
+        const results = searchFiles(fileQuery);
+        setFileResults(results);
+        setFilePickerHasResults(results.length > 0);
+      }, 150);
+      return () => clearTimeout(timer);
     }
+    setFileResults([]);
+    setFilePickerHasResults(false);
   }, [fileQuery, activeTrigger, setFilePickerHasResults]);
 
   const filteredCommands = useMemo(() => {

packages/twinki/packages/twinki/src/renderer/tui.ts

@@ -1038,7 +1038,7 @@ export class TUI extends Container {
 	 * These lines are rendered above live content and scroll into terminal scrollback.
 	 */
 	writeStaticLines(lines: string[]): void {
-		if (lines.length > 0) {
+		if (lines.length > 0 && !this.altScreen) {
 			this.accumulatedStaticOutput.push(...lines);
 			this.trimStaticOutput();
 			// When content overflowed the viewport, old active content is stuck
@@ -1266,7 +1266,8 @@ export class TUI extends Container {
 
 		// OPTIMIZED: Combine accumulated static output with live content
 		// Use concat instead of spread operator for better performance with large arrays
-		if (this.accumulatedStaticOutput.length > 0) {
+		// Skip in alt screen — no scrollback buffer to display static content in.
+		if (this.accumulatedStaticOutput.length > 0 && !this.altScreen) {
 			newLines = this.accumulatedStaticOutput.concat(newLines);
 		}
 
@@ -1410,9 +1411,29 @@ export class TUI extends Container {
 			return;
 		}
 
-		// Change above previous viewport — full redraw to clear old lines.
+		// Change above previous viewport.
+		// When content didn't shrink, re-scan only the visible viewport instead
+		// of a full redraw. This avoids flashing from off-screen animation ticks
+		// (spinners, thinking indicators) that would otherwise trigger CLEAR_ALL.
 		const previousContentViewportTop = Math.max(0, this.previousLines.length - height);
-		if (firstChanged < previousContentViewportTop) {
+		if (firstChanged < previousContentViewportTop && newLines.length >= this.previousLines.length) {
+			firstChanged = -1;
+			lastChanged = -1;
+			for (let i = previousContentViewportTop; i < Math.max(newLines.length, this.previousLines.length); i++) {
+				const oldLine = this.previousLines[i] ?? '';
+				const newLine = newLines[i] ?? '';
+				if (oldLine !== newLine) {
+					if (firstChanged === -1) firstChanged = i;
+					lastChanged = i;
+				}
+			}
+			if (firstChanged === -1) {
+				this.previousLines = newLines;
+				this.previousWidth = width;
+				this.previousViewportTop = Math.max(0, this.maxLinesRendered - height);
+				return;
+			}
+		} else if (firstChanged < previousContentViewportTop) {
 			fullRender(this.altScreen ? CLEAR_SCREEN : CLEAR_ALL, 'off-screen-change');
 			return;
 		}