fix(schema): recognize cross-realm arrays with Array.isArray

ark/schema/roots/proto.ts

@@ -4,6 +4,7 @@ import {
 	domainOf,
 	getBuiltinNameOfConstructor,
 	hasKey,
+	isArray,
 	objectKindDescriptions,
 	objectKindOrDomainOf,
 	throwParseError,
@@ -144,12 +145,20 @@ export class ProtoNode extends InternalBasis<Proto.Declaration> {
 	private readonly requiresInvalidDateCheck =
 		this.proto === Date && !this.dateAllowsInvalid
 
+	// Array.isArray is realm-safe; `instanceof Array` rejects arrays from other
+	// windows/vm contexts (https://github.com/arktypeio/arktype/issues/1597).
+	private readonly isArrayProto = this.proto === Array
+
 	traverseAllows: TraverseAllows =
 		this.requiresInvalidDateCheck ?
 			data => data instanceof Date && data.toString() !== "Invalid Date"
-		:	data => data instanceof this.proto
+		: this.isArrayProto ? data => isArray(data)
+		: data => data instanceof this.proto
 
-	compiledCondition = `data instanceof ${this.serializedConstructor}${this.requiresInvalidDateCheck ? ` && data.toString() !== "Invalid Date"` : ""}`
+	compiledCondition =
+		this.isArrayProto ? `Array.isArray(data)` : (
+			`data instanceof ${this.serializedConstructor}${this.requiresInvalidDateCheck ? ` && data.toString() !== "Invalid Date"` : ""}`
+		)
 	compiledNegation = `!(${this.compiledCondition})`
 
 	protected innerToJsonSchema(ctx: ToJsonSchema.Context): JsonSchema {

ark/type/__tests__/arrays/array.test.ts

@@ -1,5 +1,6 @@
 import { attest, contextualize } from "@ark/attest"
 import { scope, type } from "arktype"
+import { createContext, runInContext } from "node:vm"
 import { incompleteArrayTokenMessage } from "arktype/internal/parser/shift/operator/operator.ts"
 import {
 	multipleVariadicMesage,
@@ -281,4 +282,19 @@ value at [1] must be a number (was boolean)`)
 			.snap(`value at [0] must be a string (was a number)
 value at [1] must be a string (was a number)`)
 	})
+
+	it("accepts arrays from another realm", () => {
+		const foreign = runInContext("[1, 2, 3]", createContext())
+		// Same value identity check would fail: foreign instanceof Array === false
+		attest(Array.isArray(foreign)).equals(true)
+		attest(foreign instanceof Array).equals(false)
+
+		const T = type("number[]")
+		attest(T.allows(foreign)).equals(true)
+		// Don't use .equals on the array itself — foreign-realm arrays have a
+		// different constructor, which attest treats as unequal.
+		const result = T(foreign)
+		attest(result === foreign).equals(true)
+		attest([...(result as number[])]).equals([1, 2, 3])
+	})
 })

ark/util/objectKinds.ts

@@ -155,6 +155,10 @@ type instantiableObjectKind<data extends object> = {
 export const objectKindOf = <data extends object>(
 	data: data
 ): objectKindOf<data> | undefined => {
+	// Realm-safe: cross-window/vm arrays fail `instanceof Array` but pass
+	// Array.isArray (https://github.com/arktypeio/arktype/issues/1597).
+	if (Array.isArray(data)) return "Array" as never
+
 	let prototype: Partial<Object> | null = Object.getPrototypeOf(data)
 	while (
 		prototype?.constructor &&