chore(vendor): import pi 0.85.1

Imported as a linear vendor commit so forge rebases do not replay the upstream root tree.

git-subtree-dir: third_party/pi

git-subtree-split: d981de1229ef899957bbe968bc8dcda02a21f477

third_party/pi/packages/tui/src/components/mouse-region.ts

@@ -0,0 +1,33 @@
+import {
+	type Component,
+	dispatchMouseEvent,
+	type TuiMouseDispatchResult,
+	type TuiMouseEvent,
+	type TuiMouseEventResult,
+} from "../tui.ts";
+
+export type MouseRegionHandler = (event: TuiMouseEvent) => TuiMouseEventResult | undefined;
+
+/** Adds mouse handling to an existing component without changing its rendering. */
+export class MouseRegion implements Component {
+	private readonly child: Component;
+	private readonly onMouse: MouseRegionHandler;
+
+	constructor(child: Component, onMouse: MouseRegionHandler) {
+		this.child = child;
+		this.onMouse = onMouse;
+	}
+
+	render(width: number): string[] {
+		return this.child.render(width);
+	}
+
+	handleMouse(event: TuiMouseEvent): TuiMouseDispatchResult | TuiMouseEventResult | undefined {
+		const childResult = dispatchMouseEvent(this.child, event);
+		return childResult ?? this.onMouse(event);
+	}
+
+	invalidate(): void {
+		this.child.invalidate();
+	}
+}