fix(tui): avoid throttling keyboard input

packages/tui/CHANGELOG.md

@@ -13,6 +13,7 @@
 - Fixed alternate-screen Kitty images crossing vertical layout clip boundaries and overlapping sticky regions while scrolling.
 - Fixed alternate-screen redraws retransmitting Kitty image data when placements move or recently offscreen images return, dropping adjacent row content when reusing placements, rendering fixed-basis scroll content twice per frame, and scanning clipped transcript rows while painting.
 - Fixed fullscreen transcript navigation leaving no editor-accessible `Home`, `End`, `PageUp`, or `PageDown` variants by adding Ctrl-modified editor bindings ([#7574](https://github.com/earendil-works/pi/issues/7574)).
+- Fixed keyboard input rendering latency on Windows by letting input preempt the throttled render timer.
 
 ### Added
 

packages/tui/src/tui.ts

@@ -337,6 +337,7 @@ export abstract class TuiBase extends Container implements TUI {
 	/** Global callback for debug key (Shift+Ctrl+D). Called before input is forwarded to focused component. */
 	public onDebug?: () => void;
 	private renderRequested = false;
+	private immediateRenderScheduled = false;
 	private renderTimer: NodeJS.Timeout | undefined;
 	private lastRenderAt = 0;
 	private static readonly MIN_RENDER_INTERVAL_MS = 16;
@@ -743,10 +744,7 @@ export abstract class TuiBase extends Container implements TUI {
 
 	stop(options: TuiStopOptions = {}): void {
 		this.stopped = true;
-		if (this.renderTimer) {
-			clearTimeout(this.renderTimer);
-			this.renderTimer = undefined;
-		}
+		this.cancelRenderTimer();
 		if (this.terminalColorSchemeNotificationsEnabled) {
 			this.terminal.write("\x1b[?2031l");
 		}
@@ -759,10 +757,7 @@ export abstract class TuiBase extends Container implements TUI {
 	renderNow(force = false): void {
 		if (force) this.resetRenderState();
 		this.renderRequested = false;
-		if (this.renderTimer) {
-			clearTimeout(this.renderTimer);
-			this.renderTimer = undefined;
-		}
+		this.cancelRenderTimer();
 		this.lastRenderAt = performance.now();
 		this.doRender();
 	}
@@ -770,19 +765,7 @@ export abstract class TuiBase extends Container implements TUI {
 	requestRender(force = false): void {
 		if (force) {
 			this.resetRenderState();
-			if (this.renderTimer) {
-				clearTimeout(this.renderTimer);
-				this.renderTimer = undefined;
-			}
-			this.renderRequested = true;
-			process.nextTick(() => {
-				if (this.stopped || !this.renderRequested) {
-					return;
-				}
-				this.renderRequested = false;
-				this.lastRenderAt = performance.now();
-				this.doRender();
-			});
+			this.requestImmediateRender();
 			return;
 		}
 		if (this.renderRequested) return;
@@ -790,6 +773,29 @@ export abstract class TuiBase extends Container implements TUI {
 		process.nextTick(() => this.scheduleRender());
 	}
 
+	private requestImmediateRender(): void {
+		this.cancelRenderTimer();
+		this.renderRequested = true;
+		if (this.immediateRenderScheduled) return;
+		this.immediateRenderScheduled = true;
+		process.nextTick(() => {
+			this.immediateRenderScheduled = false;
+			if (this.stopped || !this.renderRequested) return;
+			// A previously queued scheduleRender() can create a timer before this
+			// callback runs. User input must preempt that throttled frame.
+			this.cancelRenderTimer();
+			this.renderRequested = false;
+			this.lastRenderAt = performance.now();
+			this.doRender();
+		});
+	}
+
+	private cancelRenderTimer(): void {
+		if (!this.renderTimer) return;
+		clearTimeout(this.renderTimer);
+		this.renderTimer = undefined;
+	}
+
 	private scheduleRender(): void {
 		if (this.stopped || this.renderTimer || !this.renderRequested) {
 			return;
@@ -882,7 +888,9 @@ export abstract class TuiBase extends Container implements TUI {
 				return;
 			}
 			this.focusedComponent.handleInput(data);
-			this.requestRender();
+			// Keyboard input is latency-sensitive. Avoid the throttled timer path,
+			// where even setTimeout(0) can take a full 16 ms tick on Windows.
+			this.requestImmediateRender();
 		}
 	}
 

packages/tui/test/tui-render.test.ts

@@ -24,6 +24,19 @@ class TestComponent implements Component {
 	invalidate(): void {}
 }
 
+class InputComponent extends TestComponent {
+	renderCount = 0;
+
+	override render(width: number): string[] {
+		this.renderCount += 1;
+		return super.render(width);
+	}
+
+	handleInput(data: string): void {
+		this.lines = [data];
+	}
+}
+
 class LoggingVirtualTerminal extends VirtualTerminal {
 	private writes: string[] = [];
 
@@ -75,6 +88,32 @@ function getCellItalic(terminal: VirtualTerminal, row: number, col: number): num
 	return cell.isItalic();
 }
 
+describe("TUI render scheduling", () => {
+	it("renders keyboard input without waiting for a throttled frame", async () => {
+		const terminal = new VirtualTerminal(40, 10);
+		const tui: TUI = new TuiMainScreen(terminal);
+		const component = new InputComponent();
+		component.lines = ["initial"];
+		tui.addChild(component);
+		tui.setFocus(component);
+		tui.start();
+		tui.renderNow();
+		const renderCountBeforeInput = component.renderCount;
+
+		// Queue a normal throttled render first. Keyboard input should preempt it.
+		component.lines = ["pending"];
+		tui.requestRender();
+		terminal.sendInput("first");
+		terminal.sendInput("second");
+		terminal.sendInput("typed");
+		await new Promise<void>((resolve) => process.nextTick(resolve));
+
+		assert.strictEqual(component.renderCount, renderCountBeforeInput + 1);
+		assert.deepStrictEqual(component.lines, ["typed"]);
+		tui.stop();
+	});
+});
+
 describe("TUI debug logging", () => {
 	it("writes redraw logs to the provided directory", async () => {
 		const logDir = mkdtempSync(join(tmpdir(), "pi-tui-log-"));