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/src/json.ts

@@ -0,0 +1,50 @@
+import type { JsonValue } from "./types.ts";
+
+/** Return whether a value is finite strict JSON with plain objects and no cycles. */
+export function isJsonValue(value: unknown): value is JsonValue {
+	return check(value, new Set<object>(), 0);
+}
+
+function check(value: unknown, ancestors: Set<object>, depth: number): boolean {
+	if (depth > 512) return false;
+	if (value === null || typeof value === "string" || typeof value === "boolean") return true;
+	if (typeof value === "number") return Number.isFinite(value);
+	if (Array.isArray(value)) {
+		const keys = Reflect.ownKeys(value);
+		if (keys.length !== value.length + 1 || keys.some((key) => typeof key !== "string")) return false;
+		if (ancestors.has(value)) return false;
+		ancestors.add(value);
+		try {
+			for (let index = 0; index < value.length; index++) {
+				const descriptor = Object.getOwnPropertyDescriptor(value, String(index));
+				if (
+					descriptor === undefined ||
+					!descriptor.enumerable ||
+					!("value" in descriptor) ||
+					!check(descriptor.value, ancestors, depth + 1)
+				) {
+					return false;
+				}
+			}
+			return true;
+		} finally {
+			ancestors.delete(value);
+		}
+	}
+	if (typeof value !== "object" || value === null) return false;
+	const prototype = Object.getPrototypeOf(value);
+	if (prototype !== Object.prototype && prototype !== null) return false;
+	if (Reflect.ownKeys(value).some((key) => typeof key !== "string")) return false;
+	if (ancestors.has(value)) return false;
+	ancestors.add(value);
+	try {
+		for (const descriptor of Object.values(Object.getOwnPropertyDescriptors(value))) {
+			if (!descriptor.enumerable || !("value" in descriptor) || !check(descriptor.value, ancestors, depth + 1)) {
+				return false;
+			}
+		}
+		return true;
+	} finally {
+		ancestors.delete(value);
+	}
+}