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/chord/test/boundary.test.ts

@@ -0,0 +1,34 @@
+import { readdir, readFile } from "node:fs/promises";
+import { dirname, resolve } from "node:path";
+import { fileURLToPath } from "node:url";
+import { describe, expect, test } from "vitest";
+
+const packageDirectory = resolve(dirname(fileURLToPath(import.meta.url)), "..");
+const sourceDirectory = resolve(packageDirectory, "src");
+const IMPORT_SPECIFIER = /(?:import|export)\s+(?:type\s+)?(?:[^;]*?\sfrom\s*)?["']([^"']+)["']/gu;
+
+describe("package boundary", () => {
+	test("does not depend on Pi packages or files outside Chord", async () => {
+		const manifest = JSON.parse(await readFile(resolve(packageDirectory, "package.json"), "utf8")) as {
+			dependencies?: Record<string, string>;
+		};
+		expect(Object.keys(manifest.dependencies ?? {}).filter((name) => name.startsWith("@earendil-works/pi-"))).toEqual(
+			[],
+		);
+
+		const paths = (await readdir(sourceDirectory, { recursive: true })).filter((path) => path.endsWith(".ts")).sort();
+		const violations: string[] = [];
+		for (const path of paths) {
+			const file = resolve(sourceDirectory, path);
+			const source = await readFile(file, "utf8");
+			for (const match of source.matchAll(IMPORT_SPECIFIER)) {
+				const specifier = match[1]!;
+				if (specifier.startsWith("@earendil-works/pi-")) violations.push(`${path}: ${specifier}`);
+				if (specifier.startsWith(".") && !resolve(dirname(file), specifier).startsWith(`${sourceDirectory}/`)) {
+					violations.push(`${path}: ${specifier}`);
+				}
+			}
+		}
+		expect(violations).toEqual([]);
+	});
+});