Stabilize iOS/watchOS/tvOS apps and add cross-platform audit remediation

SharedCore/Tests/SharedCoreWatchOSTests/WatchPayloadValidationTests.swift

@@ -0,0 +1,47 @@
+import XCTest
+@testable import SharedCore
+
+final class WatchPayloadValidationTests: XCTestCase {
+    private struct MockPayload: Codable, Equatable {
+        let name: String
+        let count: Int
+    }
+
+    func testValidateRejectsEmptyPayload() {
+        let error = WatchPayloadValidation.validate(Data())
+        XCTAssertEqual(error, .emptyPayload)
+    }
+
+    func testValidateRejectsOversizedPayload() {
+        let payload = Data(repeating: 0, count: 9)
+        let error = WatchPayloadValidation.validate(payload, maxBytes: 8)
+        XCTAssertEqual(error, .payloadTooLarge(actualBytes: 9, maxBytes: 8))
+    }
+
+    func testDecodeAcceptsValidPayload() throws {
+        let payload = try JSONEncoder().encode(MockPayload(name: "set", count: 12))
+        let decoded = try WatchPayloadValidation.decode(MockPayload.self, from: payload)
+        XCTAssertEqual(decoded, MockPayload(name: "set", count: 12))
+    }
+
+    func testDecodeRejectsInvalidJSON() throws {
+        let invalid = Data("not-json".utf8)
+
+        XCTAssertThrowsError(try WatchPayloadValidation.decode(MockPayload.self, from: invalid)) { error in
+            XCTAssertEqual(error as? WatchPayloadValidationError, .decodeFailure)
+        }
+    }
+
+    func testDecodeRejectsOversizedPayloadBeforeDecoding() {
+        let payload = Data(repeating: 1, count: 32)
+
+        XCTAssertThrowsError(
+            try WatchPayloadValidation.decode(MockPayload.self, from: payload, maxBytes: 16)
+        ) { error in
+            XCTAssertEqual(
+                error as? WatchPayloadValidationError,
+                .payloadTooLarge(actualBytes: 32, maxBytes: 16)
+            )
+        }
+    }
+}