fix(schema): avoid JSON.stringify crashes on ArkErrors issues slots

ark/schema/__tests__/errors.test.ts

@@ -189,6 +189,16 @@ contextualize(() => {
 		])
 	})
 
+	it("serialization tolerates indexed entries without toJSON (e.g. HTTP JSON.stringify)", () => {
+		;(errors as unknown as { push(...items: unknown[]): number }).push({
+			message: "foreign issue",
+			path: ["_"]
+		})
+		const parsed = JSON.parse(JSON.stringify(errors)) as unknown[]
+		attest(parsed.length).equals(2)
+		attest(parsed[1]).equals({ message: "foreign issue", path: ["_"] })
+	})
+
 	it("flatByPath", () => {
 		attest(errors.flatByPath).snap({
 			n: [

ark/schema/shared/errors.ts

@@ -314,8 +314,29 @@ export class ArkErrors
 		return this
 	}
 
+	/**
+	 * Also Standard Schema `issues`; HTTP stacks may `JSON.stringify` this array,
+	 * so indexed entries must not assume {@link ArkError}.
+	 */
+	private static indexedIssueToJson(issue: unknown): JsonObject {
+		if (issue === undefined) return { message: "undefined" }
+		if (issue === null) return { message: "null" }
+		if (typeof issue !== "object") return { message: String(issue) }
+
+		const toJSON = (issue as { toJSON?: unknown }).toJSON
+		if (typeof toJSON === "function") return toJSON.call(issue)
+
+		const { message, path } = issue as Record<string, unknown>
+		if (typeof message === "string") {
+			if (path === undefined) return { message }
+			return { message, path } as JsonObject
+		}
+
+		return { message: String(issue) }
+	}
+
 	toJSON(): JsonArray {
-		return [...this.map(e => e.toJSON())]
+		return [...this.map(ArkErrors.indexedIssueToJson)]
 	}
 
 	toString(): string {