create CommandStream and first Command

src/main/kotlin/eventDemo/plugins/Serialization.kt

@@ -1,5 +1,6 @@
 package eventDemo.plugins
 
+import eventDemo.app.CommandId
 import eventDemo.app.GameId
 import io.ktor.serialization.kotlinx.json.json
 import io.ktor.server.application.Application
@@ -28,6 +29,19 @@ fun Application.configureSerialization() {
     }
 }
 
+object CommandIdSerializer : KSerializer<CommandId> {
+    override fun deserialize(decoder: Decoder): CommandId = CommandId(decoder.decodeString())
+
+    override fun serialize(
+        encoder: Encoder,
+        value: CommandId,
+    ) {
+        encoder.encodeString(value.toString())
+    }
+
+    override val descriptor: SerialDescriptor = PrimitiveSerialDescriptor("CommandId", PrimitiveKind.STRING)
+}
+
 object GameIdSerializer : KSerializer<GameId> {
     override fun deserialize(decoder: Decoder): GameId = GameId(UUID.fromString(decoder.decodeString()))