fix(mac): avoid crash decoding gateway frames

apps/macos/Tests/ClawdisIPCTests/GatewayFrameDecodeTests.swift

@@ -0,0 +1,31 @@
+import Foundation
+import Testing
+import ClawdisProtocol
+
+@Suite struct GatewayFrameDecodeTests {
+    @Test func decodesEventFrameWithAnyCodablePayload() throws {
+        let json = """
+        {
+          "type": "event",
+          "event": "presence",
+          "payload": { "foo": "bar", "count": 1 },
+          "seq": 7
+        }
+        """
+
+        let frame = try JSONDecoder().decode(GatewayFrame.self, from: Data(json.utf8))
+
+        #expect({
+            if case .event = frame { true } else { false }
+        }(), "expected .event frame")
+
+        guard case let .event(evt) = frame else {
+            return
+        }
+
+        let payload = evt.payload?.value as? [String: AnyCodable]
+        #expect(payload?["foo"]?.value as? String == "bar")
+        #expect(payload?["count"]?.value as? Int == 1)
+        #expect(evt.seq == 7)
+    }
+}