fix: Refactor NettyServerConfig to use MessageCodecFactory directly (#4134)

## Summary
- Change `NettyServerConfig` to store `MessageCodecFactory` instead of
`PartialFunction`
- Add `codecFactory` getter that ensures `withMapOutput` is applied for
JSON serialization
- Update `NettyResponseHandler` to accept `MessageCodecFactory` directly
- Centralize codec factory creation to avoid duplication between
response handler and request dispatcher

This follows the suggestion from Gemini code review on #4132 to pass
`MessageCodecFactory` directly instead of `PartialFunction`, improving
maintainability by making the codec dependency more explicit.

## Test plan
- [x] Compile netty module
- [ ] CI tests pass

🤖 Generated with [Claude Code](https://claude.com/claude-code)

---------

Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>

Author: xerial

airframe-http-netty/src/main/scala/wvlet/airframe/http/netty/NettyResponseHandler.scala

@@ -22,13 +22,10 @@ import wvlet.airframe.surface.{Primitive, Surface}
 import wvlet.airframe.rx.Rx
 import wvlet.log.LogSupport
 
-class NettyResponseHandler(customCodec: PartialFunction[Surface, MessageCodec[_]] = PartialFunction.empty)
-    extends ResponseHandler[Request, Response]
+class NettyResponseHandler(
+    codecFactory: MessageCodecFactory = MessageCodecFactory.defaultFactoryForJSON
+) extends ResponseHandler[Request, Response]
     with LogSupport {
-  private val codecFactory = {
-    MessageCodecFactory.defaultFactoryForJSON
-      .withCodecs(customCodec)
-  }
 
   override def toHttpResponse[A](route: Route, request: Request, responseSurface: Surface, a: A): Response = {
     a match {

airframe-http-netty/src/main/scala/wvlet/airframe/http/netty/NettyServer.scala

@@ -52,7 +52,7 @@ case class NettyServerConfig(
     httpLoggerProvider: HttpLoggerConfig => HttpLogger = { (config: HttpLoggerConfig) =>
       new LogRotationHttpLogger(config)
     },
-    customCodec: PartialFunction[Surface, MessageCodec[_]] = PartialFunction.empty,
+    private val customCodecFactory: MessageCodecFactory = MessageCodecFactory.defaultFactory,
     // Thread manager for handling Future[_] responses
     executionContext: ExecutionContext = {
       // Using the global thread pool causes an issue in sbt's layered class loader #918
@@ -64,6 +64,11 @@ case class NettyServerConfig(
 ) {
   lazy val port = serverPort.getOrElse(IOUtil.unusedPort)
 
+  /**
+    * Get the codec factory with map output enabled for JSON serialization
+    */
+  def codecFactory: MessageCodecFactory = customCodecFactory.withMapOutput
+
   private[netty] def canUseEpoll: Boolean = {
     useEpoll && Epoll.isAvailable
   }
@@ -92,13 +97,16 @@ case class NettyServerConfig(
     )
   }
 
+  def withCodecFactory(factory: MessageCodecFactory): NettyServerConfig = {
+    this.copy(customCodecFactory = factory)
+  }
+
   def withCustomCodec(p: PartialFunction[Surface, MessageCodec[_]]): NettyServerConfig = {
-    this.copy(customCodec = p)
+    this.copy(customCodecFactory = customCodecFactory.withCodecs(p))
   }
+
   def withCustomCodec(m: Map[Surface, MessageCodec[_]]): NettyServerConfig = {
-    this.copy(customCodec = customCodec.orElse {
-      case s: Surface if m.contains(s) => m(s)
-    })
+    this.copy(customCodecFactory = customCodecFactory.withCodecs(m))
   }
 
   def newServer(session: Session): NettyServer = {
@@ -140,7 +148,7 @@ case class NettyServerConfig(
   def newHttpLogger: HttpLogger = {
     val config = httpLoggerConfig
       .withExtraEntries(() => ListMap("server_name" -> name))
-      .withCustomCodec(customCodec)
+      .withCodecFactory(codecFactory)
     httpLoggerProvider(config)
   }
 }
@@ -235,9 +243,8 @@ class NettyServer(config: NettyServerConfig, session: Session) extends HttpServe
               config.router,
               config.controllerProvider,
               NettyBackend,
-              new NettyResponseHandler(config.customCodec),
-              // Set a custom codec and use JSON map output
-              MessageCodecFactory.defaultFactoryForJSON.withCodecs(config.customCodec),
+              new NettyResponseHandler(config.codecFactory),
+              config.codecFactory,
               config.executionContext
             )
           )