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/layout-node.ts

@@ -0,0 +1,51 @@
+import type { Component } from "./tui.ts";
+
+export const LAYOUT_NODE = Symbol.for("@earendil-works/pi-tui/layout-node");
+
+export interface LayoutViewport {
+	width: number;
+	height: number;
+}
+
+export interface StackLayoutEntry {
+	component: Component;
+	basis?: number | "auto";
+	grow?: number;
+	shrink?: number;
+	minSize?: number;
+	maxSize?: number;
+	visible?: (viewport: LayoutViewport) => boolean;
+}
+
+export interface StackLayoutNode {
+	type: "vstack" | "hstack";
+	entries: readonly StackLayoutEntry[];
+	gap: number;
+	align: "stretch" | "start" | "center" | "end";
+}
+
+export interface ScrollLayoutState {
+	readonly scrollTop: number;
+	readonly primary: boolean;
+	readonly overscroll: "chain" | "contain";
+	readonly viewportHeight: number;
+	getContentWidth(width: number): number;
+	updateLayout(contentHeight: number, viewportHeight: number, requestRender: () => void): void;
+}
+
+export interface ScrollLayoutNode {
+	type: "scroll";
+	component: Component;
+	state: ScrollLayoutState;
+}
+
+export type LayoutNode = StackLayoutNode | ScrollLayoutNode;
+
+export interface LayoutComponent extends Component {
+	[LAYOUT_NODE](): LayoutNode;
+}
+
+export function getLayoutNode(component: Component): LayoutNode | undefined {
+	const candidate = component as Partial<LayoutComponent>;
+	return typeof candidate[LAYOUT_NODE] === "function" ? candidate[LAYOUT_NODE]() : undefined;
+}