Add Kotlin implementation and improve protocol documentation

2026-04-12 16:35:39 +09:00 · 2026-04-12 16:35:39 +09:00 · 2dcb532e24
commit 2dcb532e24
parent 34d06258c6
35 changed files with 4763 additions and 14 deletions
--- a/.claude/settings.json
+++ b/.claude/settings.json
@ -6,7 +6,10 @@
      "Bash(sudo apt-get:*)",
      "Bash(protoc --version)",
      "Bash(dart analyze:*)",
-      "Bash(ls *.log)"
+      "Bash(ls *.log)",
+      "Bash(tools/check_proto_sync.sh)",
+      "Bash(mv CODE_REVIEW.md code_review_0.log)",
+      "Bash(mv PLAN.md plan_0.log)"
    ],
    "additionalDirectories": [
      "/config/workspace/toki_socket/tasks"
--- a/PROTOCOL.md
+++ b/PROTOCOL.md
@ -33,7 +33,7 @@ This protocol intentionally defines only the transport-level contract shared acr
 - 4 bytes, big-endian positive integer. Dart reads/writes it as `int32`; Go reads/writes the same 4 bytes as `uint32`.
 - Value: byte length of the following `PacketBase` protobuf payload
 - Value of `0`: reserved / no-op, receiver clears buffer
- Implementations may apply safety limits to payload size. The current Dart and Go implementations reject TCP packets larger than 64 MiB.
+- Implementations may apply safety limits to payload size. The current Dart, Go, and Kotlin implementations reject TCP packets larger than 64 MiB.

 ### WebSocket / WSS

@ -111,12 +111,12 @@ On the receive side, use the same value as the registration key.
 | Dart | `T.toString()` (equals qualified name for top-level proto messages) |
 | Go | `string(proto.MessageName(m))` via `TypeNameOf(m)` |
 | C# | `typeof(T).Name` — verify matches proto qualified name |
-| Kotlin | `T::class.simpleName` — verify matches |
+| Kotlin | `descriptorForType.fullName` via `typeNameOf(m)` |
 | Swift | `String(describing: T.self)` — verify matches |
 | Python | `descriptor.name` from `MessageClass.DESCRIPTOR` — verify matches |
 | Rust | `M::default().descriptor_dyn().name().to_string()` (protobuf crate) — verify matches |

-The current packet proto has no `package` declaration, so Dart and Go both use simple names such as `TestData` and `HeartBeat`. If a future proto adds a `package`, `proto.MessageName` may become fully qualified, and all implementations must use the same value.
+The current packet proto has no `package` declaration, so Dart, Go, and Kotlin all use simple names such as `TestData` and `HeartBeat`. If a future proto adds a `package`, `proto.MessageName` may become fully qualified, and all implementations must use the same value.

 **Important**: Verify typeName consistency across languages before connecting heterogeneous clients.

@ -177,7 +177,7 @@ Sending `HeartBeat {}`:
 |----------|--------|------|
 | Dart | Available | `dart/` |
 | C# (Unity) | Planned | `csharp/` |
-| Kotlin | Planned | `kotlin/` |
+| Kotlin | In progress | `kotlin/` |
 | Swift | Planned | `swift/` |
 | Go | Available | `go/` |
 | Python | Planned | `python/` |
@ -190,4 +190,4 @@ Sending `HeartBeat {}`:
 `dart/lib/src/packets/message_common.proto` is the canonical packet definition.
 All language implementations must keep the same message schema and generate bindings from it.

-The Go implementation keeps a copy at `go/packets/message_common.proto` because Go generation needs `option go_package`. Keep the message fields in sync with the canonical Dart proto before regenerating `go/packets/message_common.pb.go`.
+The Go implementation keeps a copy at `go/packets/message_common.proto` because Go generation needs `option go_package`. The Kotlin implementation keeps a copy at `kotlin/src/main/proto/message_common.proto` for Java/Kotlin generation options. Keep the message fields in sync with the canonical Dart proto before regenerating language bindings.
--- a/README.md
+++ b/README.md
@ -36,7 +36,7 @@ Protocol compatibility is tracked separately from language package versions. See
 |----------|--------|------|----------|
 | Dart | Available | [dart/](dart/) | Flutter, Dart server |
 | C# | Planned | `csharp/` | Unity, .NET |
-| Kotlin | Planned | `kotlin/` | Android |
+| Kotlin | In progress | [kotlin/](kotlin/) | Android, JVM |
 | Swift | Planned | `swift/` | iOS, macOS |
 | Go | Available | [go/](go/) | Server, tooling, scripting |
 | Python | Planned | `python/` | Server, tooling, scripting |
@ -91,7 +91,7 @@ tools/generate_proto.sh
 tools/check_proto_sync.sh
 ```

-The Go proto copy is allowed to keep only its Go-specific `option go_package` difference. `tools/check_proto_sync.sh` fails with a diff when the message schema drifts.
+The Go and Kotlin proto copies are allowed to keep only language-specific options such as `option go_package` or Java package/class options. `tools/check_proto_sync.sh` fails with a diff when the message schema drifts.

 ---

@ -180,6 +180,29 @@ cd go
 go test ./...
 ```

+```bash
+cd kotlin
+./gradlew test
+```
+
+Cross-language checks:
+
+```bash
+cd go
+go run ./crosstest/go_dart.go
+go run ./crosstest/go_kotlin.go
+```
+
+```bash
+cd dart
+dart run crosstest/dart_go.dart
+```
+
+```bash
+cd kotlin
+./gradlew run -PmainClass=com.tokilabs.toki_socket.crosstest.KotlinGoKt
+```
+
 When proto files change, also run:

 ```bash
--- a/go/crosstest/go_dart.go
+++ b/go/crosstest/go_dart.go
@ -1,3 +1,5 @@
+//go:build ignore
+
 package main

 import (
--- a/go/crosstest/go_kotlin.go
+++ b/go/crosstest/go_kotlin.go
@ -0,0 +1,324 @@
+//go:build ignore
+
+package main
+
+import (
+	"bufio"
+	"context"
+	"errors"
+	"fmt"
+	"io"
+	"net"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"regexp"
+	"runtime"
+	"sync"
+	"time"
+
+	"google.golang.org/protobuf/proto"
+	"nhooyr.io/websocket"
+
+	toki "toki-labs.com/toki_socket/go"
+	"toki-labs.com/toki_socket/go/packets"
+)
+
+const (
+	host                    = "127.0.0.1"
+	goKotlinTCPPort         = 29290
+	goKotlinWSPort          = 29292
+	wsPath                  = "/"
+	processTimeout          = 20 * time.Second
+	serverObservationWindow = 200 * time.Millisecond
+)
+
+func parserMap() toki.ParserMap {
+	return toki.ParserMap{
+		toki.TypeNameOf(&packets.TestData{}): func(b []byte) (proto.Message, error) {
+			m := &packets.TestData{}
+			return m, proto.Unmarshal(b, m)
+		},
+	}
+}
+
+func main() {
+	fmt.Printf("INFO typeName go=%s\n", toki.TypeNameOf(&packets.TestData{}))
+	if err := run(); err != nil {
+		fmt.Fprintf(os.Stderr, "FAIL crosstest error=%v\n", err)
+		os.Exit(1)
+	}
+	fmt.Println("PASS all go-server/kotlin-client crosstests passed")
+}
+
+func run() error {
+	if err := runTCPSendPush(); err != nil {
+		return err
+	}
+	time.Sleep(150 * time.Millisecond)
+	if err := runTCPRequests(); err != nil {
+		return err
+	}
+	time.Sleep(150 * time.Millisecond)
+	if err := runWSSendPush(); err != nil {
+		return err
+	}
+	time.Sleep(150 * time.Millisecond)
+	return runWSRequests()
+}
+
+func runTCPSendPush() error {
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+
+	received := make(chan bool, 1)
+	server := toki.NewTcpServer(host, goKotlinTCPPort, func(conn net.Conn) *toki.TcpClient {
+		return toki.NewTcpClient(conn, 0, 0, parserMap())
+	})
+	server.OnClientConnected = func(client *toki.TcpClient) {
+		toki.AddListenerTyped[*packets.TestData](&client.Communicator, func(data *packets.TestData) {
+			fmt.Printf("SERVER_RECEIVED index=%d message=%s\n", data.GetIndex(), data.GetMessage())
+			valid := data.GetIndex() == 101 && data.GetMessage() == "fire from kotlin client"
+			select {
+			case received <- valid:
+			default:
+			}
+			if valid {
+				_ = client.Send(&packets.TestData{Index: 200, Message: "push from go server"})
+			}
+		})
+	}
+	if err := server.Start(ctx); err != nil {
+		return err
+	}
+	defer server.Stop()
+
+	if err := runKotlinClient("tcp", goKotlinTCPPort, "send-push", map[string]bool{"1": true, "2": true}); err != nil {
+		return err
+	}
+	select {
+	case ok := <-received:
+		if !ok {
+			return errors.New("TCP send-push server received unexpected data")
+		}
+	case <-time.After(serverObservationWindow):
+		return errors.New("TCP send-push server did not receive expected data")
+	}
+	return nil
+}
+
+func runTCPRequests() error {
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+
+	server := toki.NewTcpServer(host, goKotlinTCPPort, func(conn net.Conn) *toki.TcpClient {
+		return toki.NewTcpClient(conn, 0, 0, parserMap())
+	})
+	server.OnClientConnected = func(client *toki.TcpClient) {
+		toki.AddRequestListenerTyped[*packets.TestData, *packets.TestData](&client.Communicator, func(req *packets.TestData) (*packets.TestData, error) {
+			return &packets.TestData{
+				Index:   req.GetIndex() * 2,
+				Message: "echo: " + req.GetMessage(),
+			}, nil
+		})
+	}
+	if err := server.Start(ctx); err != nil {
+		return err
+	}
+	defer server.Stop()
+
+	return runKotlinClient("tcp", goKotlinTCPPort, "requests", map[string]bool{"3": true, "4": true})
+}
+
+func runWSSendPush() error {
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+
+	received := make(chan bool, 1)
+	server := toki.NewWsServer(host, goKotlinWSPort, wsPath, func(conn *websocket.Conn) *toki.WsClient {
+		return toki.NewWsClient(conn, 0, 0, parserMap())
+	})
+	server.OnClientConnected = func(client *toki.WsClient) {
+		toki.AddListenerTyped[*packets.TestData](&client.Communicator, func(data *packets.TestData) {
+			fmt.Printf("SERVER_RECEIVED index=%d message=%s\n", data.GetIndex(), data.GetMessage())
+			valid := data.GetIndex() == 101 && data.GetMessage() == "fire from kotlin client"
+			select {
+			case received <- valid:
+			default:
+			}
+			if valid {
+				_ = client.Send(&packets.TestData{Index: 200, Message: "push from go server"})
+			}
+		})
+	}
+	if err := server.Start(ctx); err != nil {
+		return err
+	}
+	defer server.Stop()
+
+	if err := runKotlinClient("ws", goKotlinWSPort, "send-push", map[string]bool{"1": true, "2": true}); err != nil {
+		return err
+	}
+	select {
+	case ok := <-received:
+		if !ok {
+			return errors.New("WS send-push server received unexpected data")
+		}
+	case <-time.After(serverObservationWindow):
+		return errors.New("WS send-push server did not receive expected data")
+	}
+	return nil
+}
+
+func runWSRequests() error {
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+
+	server := toki.NewWsServer(host, goKotlinWSPort, wsPath, func(conn *websocket.Conn) *toki.WsClient {
+		return toki.NewWsClient(conn, 0, 0, parserMap())
+	})
+	server.OnClientConnected = func(client *toki.WsClient) {
+		toki.AddRequestListenerTyped[*packets.TestData, *packets.TestData](&client.Communicator, func(req *packets.TestData) (*packets.TestData, error) {
+			return &packets.TestData{
+				Index:   req.GetIndex() * 2,
+				Message: "echo: " + req.GetMessage(),
+			}, nil
+		})
+	}
+	if err := server.Start(ctx); err != nil {
+		return err
+	}
+	defer server.Stop()
+
+	return runKotlinClient("ws", goKotlinWSPort, "requests", map[string]bool{"3": true, "4": true})
+}
+
+func runKotlinClient(mode string, port int, phase string, expected map[string]bool) error {
+	ctx, cancel := context.WithTimeout(context.Background(), processTimeout)
+	defer cancel()
+
+	kotlinDir, err := kotlinPackageDir()
+	if err != nil {
+		return err
+	}
+
+	cmd := exec.CommandContext(ctx, "./gradlew", "run",
+		"--args=--mode="+mode+" --port="+fmt.Sprint(port)+" --phase="+phase,
+	)
+	cmd.Dir = kotlinDir
+
+	stdoutPipe, err := cmd.StdoutPipe()
+	if err != nil {
+		return err
+	}
+	stderrPipe, err := cmd.StderrPipe()
+	if err != nil {
+		return err
+	}
+	if err := cmd.Start(); err != nil {
+		return err
+	}
+
+	var mu sync.Mutex
+	var resultLines []string
+	var wg sync.WaitGroup
+	wg.Add(2)
+	go scanLines(&wg, stdoutPipe, os.Stdout, &mu, &resultLines)
+	go scanLines(&wg, stderrPipe, os.Stderr, nil, nil)
+
+	waitErr := cmd.Wait()
+	wg.Wait()
+	if ctx.Err() == context.DeadlineExceeded {
+		return fmt.Errorf("kotlin client %s/%s timed out", mode, phase)
+	}
+	return validateResultLines("kotlin-client "+mode+"/"+phase, waitErr, resultLines, expected)
+}
+
+func kotlinPackageDir() (string, error) {
+	candidates := make([]string, 0, 3)
+
+	_, filename, _, ok := runtime.Caller(0)
+	if ok {
+		repoRoot := filepath.Dir(filepath.Dir(filepath.Dir(filename)))
+		candidates = append(candidates, filepath.Join(repoRoot, "kotlin"))
+	}
+	if wd, err := os.Getwd(); err == nil {
+		candidates = append(candidates, findKotlinPackageCandidates(wd)...)
+	}
+	if executable, err := os.Executable(); err == nil {
+		candidates = append(candidates, findKotlinPackageCandidates(filepath.Dir(executable))...)
+	}
+
+	for _, candidate := range candidates {
+		if isKotlinPackageDir(candidate) {
+			return candidate, nil
+		}
+	}
+	return "", fmt.Errorf("cannot resolve kotlin package directory from candidates %v", candidates)
+}
+
+func findKotlinPackageCandidates(start string) []string {
+	candidates := make([]string, 0)
+	for dir := start; ; dir = filepath.Dir(dir) {
+		candidates = append(candidates, filepath.Join(dir, "kotlin"))
+		if filepath.Base(dir) == "kotlin" {
+			candidates = append(candidates, dir)
+		}
+		parent := filepath.Dir(dir)
+		if parent == dir {
+			return candidates
+		}
+	}
+}
+
+func isKotlinPackageDir(dir string) bool {
+	info, err := os.Stat(filepath.Join(dir, "build.gradle.kts"))
+	return err == nil && !info.IsDir()
+}
+
+func scanLines(wg *sync.WaitGroup, reader io.Reader, writer *os.File, mu *sync.Mutex, resultLines *[]string) {
+	defer wg.Done()
+	scanner := bufio.NewScanner(reader)
+	for scanner.Scan() {
+		line := scanner.Text()
+		fmt.Fprintln(writer, line)
+		if mu != nil && startsWithResult(line) {
+			mu.Lock()
+			*resultLines = append(*resultLines, line)
+			mu.Unlock()
+		}
+	}
+}
+
+func validateResultLines(label string, waitErr error, lines []string, expected map[string]bool) error {
+	failed := make([]string, 0)
+	passed := make(map[string]bool)
+	re := regexp.MustCompile(`scenario=([^ ]+)`)
+	for _, line := range lines {
+		if len(line) >= 5 && line[:5] == "FAIL " {
+			failed = append(failed, line)
+			continue
+		}
+		if len(line) >= 5 && line[:5] == "PASS " {
+			match := re.FindStringSubmatch(line)
+			if len(match) == 2 {
+				passed[match[1]] = true
+			}
+		}
+	}
+
+	missing := make([]string, 0)
+	for scenario := range expected {
+		if !passed[scenario] {
+			missing = append(missing, scenario)
+		}
+	}
+	if waitErr != nil || len(failed) > 0 || len(missing) > 0 {
+		return fmt.Errorf("%s failed waitErr=%v failed=%v missing=%v", label, waitErr, failed, missing)
+	}
+	return nil
+}
+
+func startsWithResult(line string) bool {
+	return (len(line) >= 5 && line[:5] == "PASS ") || (len(line) >= 5 && line[:5] == "FAIL ")
+}
--- a/go/crosstest/kotlin_go_client/main.go
+++ b/go/crosstest/kotlin_go_client/main.go
@ -0,0 +1,205 @@
+package main
+
+import (
+	"context"
+	"flag"
+	"fmt"
+	"os"
+	"sync"
+	"time"
+
+	"google.golang.org/protobuf/proto"
+
+	toki "toki-labs.com/toki_socket/go"
+	"toki-labs.com/toki_socket/go/packets"
+)
+
+const (
+	host          = "127.0.0.1"
+	wsPath        = "/"
+	connectWindow = 3 * time.Second
+	requestWindow = 2 * time.Second
+)
+
+type clientHandle struct {
+	communicator *toki.Communicator
+	send         func(proto.Message) error
+	close        func() error
+}
+
+func parserMap() toki.ParserMap {
+	return toki.ParserMap{
+		toki.TypeNameOf(&packets.TestData{}): func(b []byte) (proto.Message, error) {
+			m := &packets.TestData{}
+			return m, proto.Unmarshal(b, m)
+		},
+	}
+}
+
+func main() {
+	mode := flag.String("mode", "tcp", "transport mode: tcp or ws")
+	port := flag.Int("port", 0, "server port")
+	phase := flag.String("phase", "send-push", "test phase: send-push or requests")
+	flag.Parse()
+
+	fmt.Printf("INFO typeName go=%s\n", toki.TypeNameOf(&packets.TestData{}))
+
+	if *port == 0 {
+		fail("setup", "port is required")
+		os.Exit(1)
+	}
+
+	client, err := dialWithRetry(*mode, *port)
+	if err != nil {
+		fail("setup", err.Error())
+		os.Exit(1)
+	}
+	defer client.close()
+
+	var ok bool
+	switch *phase {
+	case "send-push":
+		ok = runSendPush(client)
+	case "requests":
+		ok = runRequests(client)
+	default:
+		fail("setup", fmt.Sprintf("unknown phase %q", *phase))
+		ok = false
+	}
+	if !ok {
+		os.Exit(1)
+	}
+}
+
+func dialWithRetry(mode string, port int) (*clientHandle, error) {
+	deadline := time.Now().Add(connectWindow)
+	var lastErr error
+	for time.Now().Before(deadline) {
+		ctx, cancel := context.WithTimeout(context.Background(), 300*time.Millisecond)
+		handle, err := dial(ctx, mode, port)
+		cancel()
+		if err == nil {
+			return handle, nil
+		}
+		lastErr = err
+		time.Sleep(100 * time.Millisecond)
+	}
+	return nil, fmt.Errorf("connect %s:%d timed out: %w", mode, port, lastErr)
+}
+
+func dial(ctx context.Context, mode string, port int) (*clientHandle, error) {
+	switch mode {
+	case "tcp":
+		client, err := toki.DialTcp(ctx, host, port, 0, 0, parserMap())
+		if err != nil {
+			return nil, err
+		}
+		return &clientHandle{
+			communicator: &client.Communicator,
+			send:         client.Send,
+			close:        client.Close,
+		}, nil
+	case "ws":
+		client, err := toki.DialWsWithHeartbeat(ctx, host, port, wsPath, 0, 0, parserMap())
+		if err != nil {
+			return nil, err
+		}
+		return &clientHandle{
+			communicator: &client.Communicator,
+			send:         client.Send,
+			close:        client.Close,
+		}, nil
+	default:
+		return nil, fmt.Errorf("unknown mode %q", mode)
+	}
+}
+
+func runSendPush(client *clientHandle) bool {
+	pushCh := make(chan *packets.TestData, 1)
+	toki.AddListenerTyped[*packets.TestData](client.communicator, func(msg *packets.TestData) {
+		pushCh <- msg
+	})
+
+	err := client.send(&packets.TestData{
+		Index:   101,
+		Message: "fire from go client",
+	})
+	if err != nil {
+		fail("1", err.Error())
+		return false
+	}
+	pass("1", "fire-and-forget sent")
+
+	select {
+	case msg := <-pushCh:
+		if msg.GetIndex() != 200 || msg.GetMessage() != "push from kotlin server" {
+			fail("2", fmt.Sprintf("unexpected push index=%d message=%q", msg.GetIndex(), msg.GetMessage()))
+			return false
+		}
+		pass("2", "received push from kotlin server")
+		return true
+	case <-time.After(requestWindow):
+		fail("2", "timeout waiting for server push")
+		return false
+	}
+}
+
+func runRequests(client *clientHandle) bool {
+	res, err := toki.SendRequestTyped[*packets.TestData, *packets.TestData](
+		client.communicator,
+		&packets.TestData{Index: 21, Message: "single request from go"},
+		requestWindow,
+	)
+	if err != nil {
+		fail("3", err.Error())
+		return false
+	}
+	if res.GetIndex() != 42 || res.GetMessage() != "echo: single request from go" {
+		fail("3", fmt.Sprintf("unexpected response index=%d message=%q", res.GetIndex(), res.GetMessage()))
+		return false
+	}
+	pass("3", "single request response matched")
+
+	const count = 5
+	var wg sync.WaitGroup
+	errCh := make(chan error, count)
+	for i := 0; i < count; i++ {
+		i := i
+		wg.Add(1)
+		go func() {
+			defer wg.Done()
+			index := int32(30 + i)
+			message := fmt.Sprintf("multi request %d from go", i)
+			res, err := toki.SendRequestTyped[*packets.TestData, *packets.TestData](
+				client.communicator,
+				&packets.TestData{Index: index, Message: message},
+				requestWindow,
+			)
+			if err != nil {
+				errCh <- err
+				return
+			}
+			if res.GetIndex() != index*2 || res.GetMessage() != "echo: "+message {
+				errCh <- fmt.Errorf("request %d got index=%d message=%q", i, res.GetIndex(), res.GetMessage())
+			}
+		}()
+	}
+	wg.Wait()
+	close(errCh)
+	for err := range errCh {
+		if err != nil {
+			fail("4", err.Error())
+			return false
+		}
+	}
+	pass("4", "concurrent request responses matched")
+	return true
+}
+
+func pass(scenario, detail string) {
+	fmt.Printf("PASS scenario=%s detail=%s\n", scenario, detail)
+}
+
+func fail(scenario, detail string) {
+	fmt.Printf("FAIL scenario=%s error=%s\n", scenario, detail)
+}
--- a/kotlin/build.gradle.kts
+++ b/kotlin/build.gradle.kts
@ -0,0 +1,64 @@
+plugins {
+    kotlin("jvm") version "2.0.0"
+    application
+    id("com.google.protobuf") version "0.9.4"
+}
+
+group = "com.tokilabs"
+version = "0.1.0"
+
+kotlin {
+    jvmToolchain(17)
+}
+
+sourceSets {
+    create("crosstest") {
+        kotlin.srcDir("crosstest")
+        compileClasspath += sourceSets["main"].output + configurations["runtimeClasspath"]
+        runtimeClasspath += output + compileClasspath
+    }
+}
+
+dependencies {
+    implementation("org.jetbrains.kotlinx:kotlinx-coroutines-core:1.8.1")
+    implementation("com.google.protobuf:protobuf-kotlin:4.27.0")
+    implementation("com.squareup.okhttp3:okhttp:4.12.0")
+    implementation("org.java-websocket:Java-WebSocket:1.5.6")
+
+    testImplementation("org.jetbrains.kotlinx:kotlinx-coroutines-test:1.8.1")
+    testImplementation(kotlin("test"))
+}
+
+protobuf {
+    protoc {
+        artifact = "com.google.protobuf:protoc:4.27.0"
+    }
+    generateProtoTasks {
+        all().forEach { task ->
+            task.builtins {
+                create("kotlin")
+            }
+        }
+    }
+}
+
+application {
+    mainClass.set(
+        (findProperty("mainClass") as String?)
+            ?: "com.tokilabs.toki_socket.crosstest.MainKt",
+    )
+}
+
+val crosstestSourceSet = sourceSets["crosstest"]
+
+tasks.named<JavaExec>("run") {
+    classpath = crosstestSourceSet.runtimeClasspath
+    mainClass.set(
+        (findProperty("mainClass") as String?)
+            ?: "com.tokilabs.toki_socket.crosstest.MainKt",
+    )
+}
+
+tasks.test {
+    useJUnitPlatform()
+}
--- a/kotlin/crosstest/go_kotlin_client/src/main/kotlin/com/tokilabs/toki_socket/crosstest/Main.kt
+++ b/kotlin/crosstest/go_kotlin_client/src/main/kotlin/com/tokilabs/toki_socket/crosstest/Main.kt
@ -0,0 +1,208 @@
+package com.tokilabs.toki_socket.crosstest
+
+import com.tokilabs.toki_socket.DialTcp
+import com.tokilabs.toki_socket.DialWs
+import com.tokilabs.toki_socket.ParserMap
+import com.tokilabs.toki_socket.WsClient
+import com.tokilabs.toki_socket.TcpClient
+import com.tokilabs.toki_socket.addListenerTyped
+import com.tokilabs.toki_socket.sendRequestTyped
+import com.tokilabs.toki_socket.typeNameOf
+import com.tokilabs.toki_socket.packets.TestData
+import kotlinx.coroutines.CompletableDeferred
+import kotlinx.coroutines.async
+import kotlinx.coroutines.coroutineScope
+import kotlinx.coroutines.delay
+import kotlinx.coroutines.runBlocking
+import kotlinx.coroutines.withTimeout
+import kotlin.system.exitProcess
+
+private const val HOST = "127.0.0.1"
+private const val WS_PATH = "/"
+private const val CONNECT_WINDOW_MS = 3_000L
+private const val REQUEST_WINDOW_MS = 2_000L
+
+private interface ClientHandle {
+    suspend fun send(data: TestData)
+
+    suspend fun close()
+
+    val communicator: com.tokilabs.toki_socket.Communicator
+}
+
+private class TcpHandle(
+    private val client: TcpClient,
+) : ClientHandle {
+    override val communicator = client.communicator
+
+    override suspend fun send(data: TestData) {
+        client.send(data)
+    }
+
+    override suspend fun close() {
+        client.close()
+    }
+}
+
+private class WsHandle(
+    private val client: WsClient,
+) : ClientHandle {
+    override val communicator = client.communicator
+
+    override suspend fun send(data: TestData) {
+        client.send(data)
+    }
+
+    override suspend fun close() {
+        client.close()
+    }
+}
+
+fun main(args: Array<String>) = runBlocking {
+    val mode = argValue(args, "mode") ?: "tcp"
+    val phase = argValue(args, "phase") ?: "send-push"
+    val port = argValue(args, "port")?.toIntOrNull()
+
+    println("INFO typeName kotlin=${typeNameOf<TestData>()}")
+
+    if (port == null) {
+        fail("setup", "port is required")
+        exitProcess(1)
+    }
+
+    val client = try {
+        connectWithRetry(mode, port)
+    } catch (error: Throwable) {
+        fail("setup", error.message ?: error.toString())
+        exitProcess(1)
+    }
+
+    val ok = try {
+        when (phase) {
+            "send-push" -> runSendPush(client)
+            "requests" -> runRequests(client)
+            else -> {
+                fail("setup", "unknown phase $phase")
+                false
+            }
+        }
+    } finally {
+        client.close()
+    }
+
+    if (!ok) exitProcess(1)
+}
+
+private suspend fun connectWithRetry(mode: String, port: Int): ClientHandle {
+    val deadline = System.nanoTime() + CONNECT_WINDOW_MS * 1_000_000L
+    var lastError: Throwable? = null
+    while (System.nanoTime() < deadline) {
+        try {
+            return when (mode) {
+                "tcp" -> TcpHandle(DialTcp(HOST, port, 0, 0, parserMap()))
+                "ws" -> WsHandle(DialWs(HOST, port, WS_PATH, 0, 0, parserMap()))
+                else -> error("unknown mode $mode")
+            }
+        } catch (error: Throwable) {
+            lastError = error
+            delay(100)
+        }
+    }
+    error("connect $mode:$port timed out: $lastError")
+}
+
+private suspend fun runSendPush(client: ClientHandle): Boolean {
+    val push = CompletableDeferred<TestData>()
+    addListenerTyped<TestData>(client.communicator) {
+        push.complete(it)
+    }
+
+    return try {
+        client.send(
+            TestData.newBuilder()
+                .setIndex(101)
+                .setMessage("fire from kotlin client")
+                .build(),
+        )
+        pass("1", "fire-and-forget sent")
+
+        val msg = withTimeout(REQUEST_WINDOW_MS) { push.await() }
+        if (msg.index != 200 || msg.message != "push from go server") {
+            fail("2", "unexpected push index=${msg.index} message=${msg.message}")
+            false
+        } else {
+            pass("2", "received push from go server")
+            true
+        }
+    } catch (error: Throwable) {
+        fail("2", error.message ?: error.toString())
+        false
+    }
+}
+
+private suspend fun runRequests(client: ClientHandle): Boolean =
+    try {
+        val single = sendRequestTyped<TestData, TestData>(
+            client.communicator,
+            TestData.newBuilder()
+                .setIndex(21)
+                .setMessage("single request from kotlin")
+                .build(),
+            REQUEST_WINDOW_MS,
+        )
+        if (single.index != 42 || single.message != "echo: single request from kotlin") {
+            fail("3", "unexpected response index=${single.index} message=${single.message}")
+            false
+        } else {
+            pass("3", "single request response matched")
+            runConcurrentRequests(client)
+        }
+    } catch (error: Throwable) {
+        fail("3", error.message ?: error.toString())
+        false
+    }
+
+private suspend fun runConcurrentRequests(client: ClientHandle): Boolean =
+    coroutineScope {
+        val jobs = (0 until 5).map { i ->
+            async {
+                val index = 30 + i
+                val message = "multi request $i from kotlin"
+                val res = sendRequestTyped<TestData, TestData>(
+                    client.communicator,
+                    TestData.newBuilder()
+                        .setIndex(index)
+                        .setMessage(message)
+                        .build(),
+                    REQUEST_WINDOW_MS,
+                )
+                check(res.index == index * 2 && res.message == "echo: $message") {
+                    "request $i got index=${res.index} message=${res.message}"
+                }
+            }
+        }
+        try {
+            jobs.forEach { it.await() }
+            pass("4", "concurrent request responses matched")
+            true
+        } catch (error: Throwable) {
+            fail("4", error.message ?: error.toString())
+            false
+        }
+    }
+
+private fun parserMap(): ParserMap =
+    mapOf(typeNameOf<TestData>() to { TestData.parseFrom(it) })
+
+private fun argValue(args: Array<String>, name: String): String? {
+    val prefix = "--$name="
+    return args.firstOrNull { it.startsWith(prefix) }?.substring(prefix.length)
+}
+
+private fun pass(scenario: String, detail: String) {
+    println("PASS scenario=$scenario detail=$detail")
+}
+
+private fun fail(scenario: String, error: String) {
+    println("FAIL scenario=$scenario error=$error")
+}
--- a/kotlin/crosstest/kotlin_go.kt
+++ b/kotlin/crosstest/kotlin_go.kt
@ -0,0 +1,233 @@
+@file:JvmName("KotlinGoKt")
+
+package com.tokilabs.toki_socket.crosstest
+
+import com.tokilabs.toki_socket.TcpClient
+import com.tokilabs.toki_socket.TcpServer
+import com.tokilabs.toki_socket.ParserMap
+import com.tokilabs.toki_socket.WsClient
+import com.tokilabs.toki_socket.WsServer
+import com.tokilabs.toki_socket.addListenerTyped
+import com.tokilabs.toki_socket.addRequestListenerTyped
+import com.tokilabs.toki_socket.typeNameOf
+import com.tokilabs.toki_socket.packets.TestData
+import kotlinx.coroutines.CompletableDeferred
+import kotlinx.coroutines.coroutineScope
+import kotlinx.coroutines.delay
+import kotlinx.coroutines.launch
+import kotlinx.coroutines.runBlocking
+import kotlinx.coroutines.withTimeoutOrNull
+import java.io.File
+import java.util.concurrent.TimeUnit
+import kotlin.system.exitProcess
+
+private const val HOST = "127.0.0.1"
+private const val TCP_PORT = 29390
+private const val WS_PORT = 29392
+private const val WS_PATH = "/"
+private const val PROCESS_TIMEOUT_MS = 20_000L
+private const val SERVER_OBSERVATION_MS = 200L
+
+fun main() = runBlocking {
+    println("INFO typeName kotlin=${typeNameOf<TestData>()}")
+    try {
+        runTcpSendPush()
+        delay(150)
+        runTcpRequests()
+        delay(150)
+        runWsSendPush()
+        delay(150)
+        runWsRequests()
+        println("PASS all kotlin-server/go-client crosstests passed")
+    } catch (error: Throwable) {
+        System.err.println("FAIL crosstest error=${error.message ?: error}")
+        exitProcess(1)
+    }
+}
+
+private suspend fun runTcpSendPush() = coroutineScope {
+    val received = CompletableDeferred<Boolean>()
+    val server = TcpServer(HOST, TCP_PORT) { socket ->
+        TcpClient.fromSocket(socket, 0, 0, parserMap())
+    }
+    server.onClientConnected = { client ->
+        addListenerTyped<TestData>(client.communicator) { data ->
+            println("SERVER_RECEIVED index=${data.index} message=${data.message}")
+            val valid = data.index == 101 && data.message == "fire from go client"
+            received.complete(valid)
+            if (valid) {
+                launch {
+                    client.send(
+                        TestData.newBuilder()
+                            .setIndex(200)
+                            .setMessage("push from kotlin server")
+                            .build(),
+                    )
+                }
+            }
+        }
+    }
+    withServer(server::start, server::stop) {
+        runGoClient("tcp", TCP_PORT, "send-push", setOf("1", "2"))
+        val ok = withTimeoutOrNull(SERVER_OBSERVATION_MS) { received.await() } ?: false
+        check(ok) { "TCP send-push server did not receive expected data" }
+    }
+}
+
+private suspend fun runTcpRequests() {
+    val server = TcpServer(HOST, TCP_PORT) { socket ->
+        TcpClient.fromSocket(socket, 0, 0, parserMap())
+    }
+    server.onClientConnected = { client ->
+        addRequestListenerTyped<TestData, TestData>(client.communicator) { req ->
+            TestData.newBuilder()
+                .setIndex(req.index * 2)
+                .setMessage("echo: ${req.message}")
+                .build()
+        }
+    }
+    withServer(server::start, server::stop) {
+        runGoClient("tcp", TCP_PORT, "requests", setOf("3", "4"))
+    }
+}
+
+private suspend fun runWsSendPush() = coroutineScope {
+    val received = CompletableDeferred<Boolean>()
+    val server = WsServer(HOST, WS_PORT, WS_PATH) { conn ->
+        WsClient.forServer(conn, 0, 0, parserMap())
+    }
+    server.onClientConnected = { client ->
+        addListenerTyped<TestData>(client.communicator) { data ->
+            println("SERVER_RECEIVED index=${data.index} message=${data.message}")
+            val valid = data.index == 101 && data.message == "fire from go client"
+            received.complete(valid)
+            if (valid) {
+                launch {
+                    client.send(
+                        TestData.newBuilder()
+                            .setIndex(200)
+                            .setMessage("push from kotlin server")
+                            .build(),
+                    )
+                }
+            }
+        }
+    }
+    withServer(server::start, server::stop) {
+        runGoClient("ws", WS_PORT, "send-push", setOf("1", "2"))
+        val ok = withTimeoutOrNull(SERVER_OBSERVATION_MS) { received.await() } ?: false
+        check(ok) { "WS send-push server did not receive expected data" }
+    }
+}
+
+private suspend fun runWsRequests() {
+    val server = WsServer(HOST, WS_PORT, WS_PATH) { conn ->
+        WsClient.forServer(conn, 0, 0, parserMap())
+    }
+    server.onClientConnected = { client ->
+        addRequestListenerTyped<TestData, TestData>(client.communicator) { req ->
+            TestData.newBuilder()
+                .setIndex(req.index * 2)
+                .setMessage("echo: ${req.message}")
+                .build()
+        }
+    }
+    withServer(server::start, server::stop) {
+        runGoClient("ws", WS_PORT, "requests", setOf("3", "4"))
+    }
+}
+
+private inline fun withServer(
+    start: () -> Unit,
+    stop: () -> Unit,
+    body: () -> Unit,
+) {
+    start()
+    try {
+        body()
+    } finally {
+        stop()
+    }
+}
+
+private fun runGoClient(
+    mode: String,
+    port: Int,
+    phase: String,
+    expectedScenarios: Set<String>,
+) {
+    val process = ProcessBuilder(
+        "go",
+        "run",
+        "./crosstest/kotlin_go_client",
+        "--mode=$mode",
+        "--port=$port",
+        "--phase=$phase",
+    )
+        .directory(goDir())
+        .redirectErrorStream(false)
+        .start()
+
+    val stdoutLines = mutableListOf<String>()
+    val stdoutThread = Thread {
+        process.inputStream.bufferedReader().forEachLine { line ->
+            println(line)
+            if (line.startsWith("PASS ") || line.startsWith("FAIL ")) {
+                stdoutLines.add(line)
+            }
+        }
+    }
+    val stderrThread = Thread {
+        process.errorStream.bufferedReader().forEachLine { line ->
+            System.err.println(line)
+        }
+    }
+    stdoutThread.start()
+    stderrThread.start()
+
+    val finished = process.waitFor(PROCESS_TIMEOUT_MS, TimeUnit.MILLISECONDS)
+    if (!finished) {
+        process.destroyForcibly()
+    }
+    stdoutThread.join()
+    stderrThread.join()
+
+    validateResultLines(
+        "go-client $mode/$phase",
+        if (finished) process.exitValue() else -1,
+        stdoutLines,
+        expectedScenarios,
+    )
+}
+
+private fun validateResultLines(
+    label: String,
+    exitCode: Int,
+    lines: List<String>,
+    expectedScenarios: Set<String>,
+) {
+    val failed = lines.filter { it.startsWith("FAIL ") }
+    val passed = lines
+        .filter { it.startsWith("PASS ") }
+        .mapNotNull { Regex("""scenario=([^ ]+)""").find(it)?.groupValues?.get(1) }
+        .toSet()
+    val missing = expectedScenarios - passed
+    check(exitCode == 0 && failed.isEmpty() && missing.isEmpty()) {
+        "$label failed exitCode=$exitCode failed=$failed missing=$missing"
+    }
+}
+
+private fun parserMap(): ParserMap =
+    mapOf(typeNameOf<TestData>() to { TestData.parseFrom(it) })
+
+private fun goDir(): File {
+    var dir = File(System.getProperty("user.dir")).absoluteFile
+    while (dir.parentFile != null) {
+        val candidate = File(dir, "../go").canonicalFile
+        if (File(candidate, "go.mod").isFile) return candidate
+        val direct = File(dir, "go").canonicalFile
+        if (File(direct, "go.mod").isFile) return direct
+        dir = dir.parentFile
+    }
+    error("cannot resolve go directory")
+}
--- a/kotlin/gradle/wrapper/gradle-wrapper.jar
+++ b/kotlin/gradle/wrapper/gradle-wrapper.jar
--- a/kotlin/gradle/wrapper/gradle-wrapper.properties
+++ b/kotlin/gradle/wrapper/gradle-wrapper.properties
@ -0,0 +1,7 @@
+distributionBase=GRADLE_USER_HOME
+distributionPath=wrapper/dists
+distributionUrl=https\://services.gradle.org/distributions/gradle-8.10.2-bin.zip
+networkTimeout=10000
+validateDistributionUrl=true
+zipStoreBase=GRADLE_USER_HOME
+zipStorePath=wrapper/dists
--- a/kotlin/gradlew
+++ b/kotlin/gradlew
@ -0,0 +1,252 @@
+#!/bin/sh
+
+#
+# Copyright © 2015-2021 the original authors.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      https://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+# SPDX-License-Identifier: Apache-2.0
+#
+
+##############################################################################
+#
+#   Gradle start up script for POSIX generated by Gradle.
+#
+#   Important for running:
+#
+#   (1) You need a POSIX-compliant shell to run this script. If your /bin/sh is
+#       noncompliant, but you have some other compliant shell such as ksh or
+#       bash, then to run this script, type that shell name before the whole
+#       command line, like:
+#
+#           ksh Gradle
+#
+#       Busybox and similar reduced shells will NOT work, because this script
+#       requires all of these POSIX shell features:
+#         * functions;
+#         * expansions «$var», «${var}», «${var:-default}», «${var+SET}»,
+#           «${var#prefix}», «${var%suffix}», and «$( cmd )»;
+#         * compound commands having a testable exit status, especially «case»;
+#         * various built-in commands including «command», «set», and «ulimit».
+#
+#   Important for patching:
+#
+#   (2) This script targets any POSIX shell, so it avoids extensions provided
+#       by Bash, Ksh, etc; in particular arrays are avoided.
+#
+#       The "traditional" practice of packing multiple parameters into a
+#       space-separated string is a well documented source of bugs and security
+#       problems, so this is (mostly) avoided, by progressively accumulating
+#       options in "$@", and eventually passing that to Java.
+#
+#       Where the inherited environment variables (DEFAULT_JVM_OPTS, JAVA_OPTS,
+#       and GRADLE_OPTS) rely on word-splitting, this is performed explicitly;
+#       see the in-line comments for details.
+#
+#       There are tweaks for specific operating systems such as AIX, CygWin,
+#       Darwin, MinGW, and NonStop.
+#
+#   (3) This script is generated from the Groovy template
+#       https://github.com/gradle/gradle/blob/HEAD/platforms/jvm/plugins-application/src/main/resources/org/gradle/api/internal/plugins/unixStartScript.txt
+#       within the Gradle project.
+#
+#       You can find Gradle at https://github.com/gradle/gradle/.
+#
+##############################################################################
+
+# Attempt to set APP_HOME
+
+# Resolve links: $0 may be a link
+app_path=$0
+
+# Need this for daisy-chained symlinks.
+while
+    APP_HOME=${app_path%"${app_path##*/}"}  # leaves a trailing /; empty if no leading path
+    [ -h "$app_path" ]
+do
+    ls=$( ls -ld "$app_path" )
+    link=${ls#*' -> '}
+    case $link in             #(
+      /*)   app_path=$link ;; #(
+      *)    app_path=$APP_HOME$link ;;
+    esac
+done
+
+# This is normally unused
+# shellcheck disable=SC2034
+APP_BASE_NAME=${0##*/}
+# Discard cd standard output in case $CDPATH is set (https://github.com/gradle/gradle/issues/25036)
+APP_HOME=$( cd -P "${APP_HOME:-./}" > /dev/null && printf '%s
+' "$PWD" ) || exit
+
+# Use the maximum available, or set MAX_FD != -1 to use that value.
+MAX_FD=maximum
+
+warn () {
+    echo "$*"
+} >&2
+
+die () {
+    echo
+    echo "$*"
+    echo
+    exit 1
+} >&2
+
+# OS specific support (must be 'true' or 'false').
+cygwin=false
+msys=false
+darwin=false
+nonstop=false
+case "$( uname )" in                #(
+  CYGWIN* )         cygwin=true  ;; #(
+  Darwin* )         darwin=true  ;; #(
+  MSYS* | MINGW* )  msys=true    ;; #(
+  NONSTOP* )        nonstop=true ;;
+esac
+
+CLASSPATH=$APP_HOME/gradle/wrapper/gradle-wrapper.jar
+
+
+# Determine the Java command to use to start the JVM.
+if [ -n "$JAVA_HOME" ] ; then
+    if [ -x "$JAVA_HOME/jre/sh/java" ] ; then
+        # IBM's JDK on AIX uses strange locations for the executables
+        JAVACMD=$JAVA_HOME/jre/sh/java
+    else
+        JAVACMD=$JAVA_HOME/bin/java
+    fi
+    if [ ! -x "$JAVACMD" ] ; then
+        die "ERROR: JAVA_HOME is set to an invalid directory: $JAVA_HOME
+
+Please set the JAVA_HOME variable in your environment to match the
+location of your Java installation."
+    fi
+else
+    JAVACMD=java
+    if ! command -v java >/dev/null 2>&1
+    then
+        die "ERROR: JAVA_HOME is not set and no 'java' command could be found in your PATH.
+
+Please set the JAVA_HOME variable in your environment to match the
+location of your Java installation."
+    fi
+fi
+
+# Increase the maximum file descriptors if we can.
+if ! "$cygwin" && ! "$darwin" && ! "$nonstop" ; then
+    case $MAX_FD in #(
+      max*)
+        # In POSIX sh, ulimit -H is undefined. That's why the result is checked to see if it worked.
+        # shellcheck disable=SC2039,SC3045
+        MAX_FD=$( ulimit -H -n ) ||
+            warn "Could not query maximum file descriptor limit"
+    esac
+    case $MAX_FD in  #(
+      '' | soft) :;; #(
+      *)
+        # In POSIX sh, ulimit -n is undefined. That's why the result is checked to see if it worked.
+        # shellcheck disable=SC2039,SC3045
+        ulimit -n "$MAX_FD" ||
+            warn "Could not set maximum file descriptor limit to $MAX_FD"
+    esac
+fi
+
+# Collect all arguments for the java command, stacking in reverse order:
+#   * args from the command line
+#   * the main class name
+#   * -classpath
+#   * -D...appname settings
+#   * --module-path (only if needed)
+#   * DEFAULT_JVM_OPTS, JAVA_OPTS, and GRADLE_OPTS environment variables.
+
+# For Cygwin or MSYS, switch paths to Windows format before running java
+if "$cygwin" || "$msys" ; then
+    APP_HOME=$( cygpath --path --mixed "$APP_HOME" )
+    CLASSPATH=$( cygpath --path --mixed "$CLASSPATH" )
+
+    JAVACMD=$( cygpath --unix "$JAVACMD" )
+
+    # Now convert the arguments - kludge to limit ourselves to /bin/sh
+    for arg do
+        if
+            case $arg in                                #(
+              -*)   false ;;                            # don't mess with options #(
+              /?*)  t=${arg#/} t=/${t%%/*}              # looks like a POSIX filepath
+                    [ -e "$t" ] ;;                      #(
+              *)    false ;;
+            esac
+        then
+            arg=$( cygpath --path --ignore --mixed "$arg" )
+        fi
+        # Roll the args list around exactly as many times as the number of
+        # args, so each arg winds up back in the position where it started, but
+        # possibly modified.
+        #
+        # NB: a `for` loop captures its iteration list before it begins, so
+        # changing the positional parameters here affects neither the number of
+        # iterations, nor the values presented in `arg`.
+        shift                   # remove old arg
+        set -- "$@" "$arg"      # push replacement arg
+    done
+fi
+
+
+# Add default JVM options here. You can also use JAVA_OPTS and GRADLE_OPTS to pass JVM options to this script.
+DEFAULT_JVM_OPTS='"-Xmx64m" "-Xms64m"'
+
+# Collect all arguments for the java command:
+#   * DEFAULT_JVM_OPTS, JAVA_OPTS, JAVA_OPTS, and optsEnvironmentVar are not allowed to contain shell fragments,
+#     and any embedded shellness will be escaped.
+#   * For example: A user cannot expect ${Hostname} to be expanded, as it is an environment variable and will be
+#     treated as '${Hostname}' itself on the command line.
+
+set -- \
+        "-Dorg.gradle.appname=$APP_BASE_NAME" \
+        -classpath "$CLASSPATH" \
+        org.gradle.wrapper.GradleWrapperMain \
+        "$@"
+
+# Stop when "xargs" is not available.
+if ! command -v xargs >/dev/null 2>&1
+then
+    die "xargs is not available"
+fi
+
+# Use "xargs" to parse quoted args.
+#
+# With -n1 it outputs one arg per line, with the quotes and backslashes removed.
+#
+# In Bash we could simply go:
+#
+#   readarray ARGS < <( xargs -n1 <<<"$var" ) &&
+#   set -- "${ARGS[@]}" "$@"
+#
+# but POSIX shell has neither arrays nor command substitution, so instead we
+# post-process each arg (as a line of input to sed) to backslash-escape any
+# character that might be a shell metacharacter, then use eval to reverse
+# that process (while maintaining the separation between arguments), and wrap
+# the whole thing up as a single "set" statement.
+#
+# This will of course break if any of these variables contains a newline or
+# an unmatched quote.
+#
+
+eval "set -- $(
+        printf '%s\n' "$DEFAULT_JVM_OPTS $JAVA_OPTS $GRADLE_OPTS" |
+        xargs -n1 |
+        sed ' s~[^-[:alnum:]+,./:=@_]~\\&~g; ' |
+        tr '\n' ' '
+    )" '"$@"'
+
+exec "$JAVACMD" "$@"
--- a/kotlin/gradlew.bat
+++ b/kotlin/gradlew.bat
@ -0,0 +1,94 @@
+@rem
+@rem Copyright 2015 the original author or authors.
+@rem
+@rem Licensed under the Apache License, Version 2.0 (the "License");
+@rem you may not use this file except in compliance with the License.
+@rem You may obtain a copy of the License at
+@rem
+@rem      https://www.apache.org/licenses/LICENSE-2.0
+@rem
+@rem Unless required by applicable law or agreed to in writing, software
+@rem distributed under the License is distributed on an "AS IS" BASIS,
+@rem WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+@rem See the License for the specific language governing permissions and
+@rem limitations under the License.
+@rem
+@rem SPDX-License-Identifier: Apache-2.0
+@rem
+
+@if "%DEBUG%"=="" @echo off
+@rem ##########################################################################
+@rem
+@rem  Gradle startup script for Windows
+@rem
+@rem ##########################################################################
+
+@rem Set local scope for the variables with windows NT shell
+if "%OS%"=="Windows_NT" setlocal
+
+set DIRNAME=%~dp0
+if "%DIRNAME%"=="" set DIRNAME=.
+@rem This is normally unused
+set APP_BASE_NAME=%~n0
+set APP_HOME=%DIRNAME%
+
+@rem Resolve any "." and ".." in APP_HOME to make it shorter.
+for %%i in ("%APP_HOME%") do set APP_HOME=%%~fi
+
+@rem Add default JVM options here. You can also use JAVA_OPTS and GRADLE_OPTS to pass JVM options to this script.
+set DEFAULT_JVM_OPTS="-Xmx64m" "-Xms64m"
+
+@rem Find java.exe
+if defined JAVA_HOME goto findJavaFromJavaHome
+
+set JAVA_EXE=java.exe
+%JAVA_EXE% -version >NUL 2>&1
+if %ERRORLEVEL% equ 0 goto execute
+
+echo. 1>&2
+echo ERROR: JAVA_HOME is not set and no 'java' command could be found in your PATH. 1>&2
+echo. 1>&2
+echo Please set the JAVA_HOME variable in your environment to match the 1>&2
+echo location of your Java installation. 1>&2
+
+goto fail
+
+:findJavaFromJavaHome
+set JAVA_HOME=%JAVA_HOME:"=%
+set JAVA_EXE=%JAVA_HOME%/bin/java.exe
+
+if exist "%JAVA_EXE%" goto execute
+
+echo. 1>&2
+echo ERROR: JAVA_HOME is set to an invalid directory: %JAVA_HOME% 1>&2
+echo. 1>&2
+echo Please set the JAVA_HOME variable in your environment to match the 1>&2
+echo location of your Java installation. 1>&2
+
+goto fail
+
+:execute
+@rem Setup the command line
+
+set CLASSPATH=%APP_HOME%\gradle\wrapper\gradle-wrapper.jar
+
+
+@rem Execute Gradle
+"%JAVA_EXE%" %DEFAULT_JVM_OPTS% %JAVA_OPTS% %GRADLE_OPTS% "-Dorg.gradle.appname=%APP_BASE_NAME%" -classpath "%CLASSPATH%" org.gradle.wrapper.GradleWrapperMain %*
+
+:end
+@rem End local scope for the variables with windows NT shell
+if %ERRORLEVEL% equ 0 goto mainEnd
+
+:fail
+rem Set variable GRADLE_EXIT_CONSOLE if you need the _script_ return code instead of
+rem the _cmd.exe /c_ return code!
+set EXIT_CODE=%ERRORLEVEL%
+if %EXIT_CODE% equ 0 set EXIT_CODE=1
+if not ""=="%GRADLE_EXIT_CONSOLE%" exit %EXIT_CODE%
+exit /b %EXIT_CODE%
+
+:mainEnd
+if "%OS%"=="Windows_NT" endlocal
+
+:omega
--- a/kotlin/settings.gradle.kts
+++ b/kotlin/settings.gradle.kts
@ -0,0 +1,17 @@
+pluginManagement {
+    repositories {
+        gradlePluginPortal()
+        mavenCentral()
+        google()
+    }
+}
+
+dependencyResolutionManagement {
+    repositoriesMode.set(RepositoriesMode.FAIL_ON_PROJECT_REPOS)
+    repositories {
+        mavenCentral()
+        google()
+    }
+}
+
+rootProject.name = "toki-socket-kotlin"
--- a/kotlin/src/main/kotlin/com/tokilabs/toki_socket/BaseClient.kt
+++ b/kotlin/src/main/kotlin/com/tokilabs/toki_socket/BaseClient.kt
@ -0,0 +1,104 @@
+package com.tokilabs.toki_socket
+
+import com.tokilabs.toki_socket.packets.HeartBeat
+import kotlinx.coroutines.CoroutineScope
+import kotlinx.coroutines.Dispatchers
+import kotlinx.coroutines.SupervisorJob
+import kotlinx.coroutines.cancel
+import kotlinx.coroutines.launch
+import kotlinx.coroutines.sync.Mutex
+import kotlinx.coroutines.sync.withLock
+import java.util.concurrent.CopyOnWriteArrayList
+import java.util.concurrent.atomic.AtomicBoolean
+
+abstract class BaseClient<Self : BaseClient<Self>>(
+    intervalSec: Int,
+    waitSec: Int,
+    private val doClose: () -> Unit,
+    internal val scope: CoroutineScope = CoroutineScope(SupervisorJob() + Dispatchers.IO),
+) {
+    abstract val self: Self
+    abstract val communicator: Communicator
+
+    private val heartbeatIntervalMs = intervalSec * 1000L
+    private val heartbeatWaitMs = waitSec * 1000L
+    private val closedOnce = AtomicBoolean(false)
+    private val hbMutex = Mutex()
+    private var hbTimer: HeartbeatTimer? = null
+    private var waitingHBResponse = false
+    private val disconnectListeners = CopyOnWriteArrayList<(Self) -> Unit>()
+
+    fun addDisconnectListener(handler: (Self) -> Unit) {
+        disconnectListeners.add(handler)
+    }
+
+    fun removeDisconnectListeners() {
+        disconnectListeners.clear()
+    }
+
+    open fun close() {
+        if (!closedOnce.compareAndSet(false, true)) return
+        communicator.shutdown()
+        stopHeartbeat()
+        runCatching { doClose() }
+        notifyDisconnected()
+        scope.cancel()
+    }
+
+    fun sendHeartBeat() {
+        if (!communicator.isAlive() || heartbeatIntervalMs <= 0) return
+        scope.launch {
+            hbMutex.withLock {
+                hbTimer?.stop()
+                hbTimer = HeartbeatTimer(scope, heartbeatIntervalMs) {
+                    if (!communicator.isAlive()) return@HeartbeatTimer
+                    hbMutex.withLock {
+                        waitingHBResponse = true
+                    }
+                    runCatching { communicator.send(HeartBeat.getDefaultInstance()) }
+                    hbMutex.withLock {
+                        hbTimer?.stop()
+                        hbTimer = HeartbeatTimer(scope, heartbeatWaitMs) {
+                            if (communicator.isAlive()) onDisconnected()
+                        }
+                    }
+                }
+            }
+        }
+    }
+
+    fun onHeartBeat() {
+        scope.launch {
+            val wasWaiting = hbMutex.withLock {
+                if (waitingHBResponse) {
+                    waitingHBResponse = false
+                    true
+                } else {
+                    false
+                }
+            }
+            if (!wasWaiting) {
+                runCatching { communicator.send(HeartBeat.getDefaultInstance()) }
+            }
+        }
+    }
+
+    fun stopHeartbeat() {
+        scope.launch {
+            hbMutex.withLock {
+                hbTimer?.stop()
+                hbTimer = null
+            }
+        }
+    }
+
+    fun onDisconnected() {
+        close()
+    }
+
+    private fun notifyDisconnected() {
+        val listeners = disconnectListeners.toList()
+        disconnectListeners.clear()
+        listeners.forEach { it(self) }
+    }
+}
--- a/kotlin/src/main/kotlin/com/tokilabs/toki_socket/Communicator.kt
+++ b/kotlin/src/main/kotlin/com/tokilabs/toki_socket/Communicator.kt
@ -0,0 +1,319 @@
+package com.tokilabs.toki_socket
+
+import com.google.protobuf.Message
+import com.google.protobuf.MessageLite
+import com.tokilabs.toki_socket.packets.HeartBeat
+import com.tokilabs.toki_socket.packets.PacketBase
+import kotlinx.coroutines.CompletableDeferred
+import kotlinx.coroutines.CoroutineScope
+import kotlinx.coroutines.channels.Channel
+import kotlinx.coroutines.channels.ClosedSendChannelException
+import kotlinx.coroutines.launch
+import kotlinx.coroutines.selects.select
+import kotlinx.coroutines.withTimeout
+import java.util.concurrent.ConcurrentHashMap
+import java.util.concurrent.atomic.AtomicBoolean
+import java.util.concurrent.atomic.AtomicInteger
+import java.util.concurrent.locks.ReentrantReadWriteLock
+import kotlin.concurrent.read
+import kotlin.concurrent.write
+import kotlin.reflect.KClass
+
+class NotConnectedException : IllegalStateException("not connected")
+
+interface Transport {
+    suspend fun writePacket(base: PacketBase)
+
+    fun close()
+}
+
+typealias ParserMap = Map<String, (ByteArray) -> MessageLite>
+
+private typealias RequestHandler = suspend (MessageLite, Int) -> Unit
+
+private data class PendingRequest(
+    val expectedTypeName: String,
+    val ch: Channel<MessageLite> = Channel(capacity = 1),
+    val errCh: Channel<Throwable> = Channel(capacity = 1),
+)
+
+private data class QueuedPacket(
+    val base: PacketBase,
+    val done: CompletableDeferred<Throwable?> = CompletableDeferred(),
+)
+
+fun typeNameOf(m: MessageLite): String =
+    (m as Message).descriptorForType.fullName
+
+@PublishedApi
+internal fun <T : Message> defaultMessage(kClass: KClass<T>): T {
+    val method = kClass.java.getDeclaredMethod("getDefaultInstance")
+    @Suppress("UNCHECKED_CAST")
+    return method.invoke(null) as T
+}
+
+inline fun <reified T : Message> typeNameOf(): String =
+    typeNameOf(defaultMessage(T::class))
+
+class Communicator(
+    private val transport: Transport,
+    parserMap: ParserMap,
+    private val scope: CoroutineScope,
+) {
+    private val rwLock = ReentrantReadWriteLock()
+    private val nonce = AtomicInteger(0)
+    private val isAlive = AtomicBoolean(false)
+    private val parserMap: MutableMap<String, (ByteArray) -> MessageLite> = ConcurrentHashMap()
+    private val handlers = mutableMapOf<String, MutableList<(MessageLite) -> Unit>>()
+    private val reqHandlers = mutableMapOf<String, RequestHandler>()
+    private val pendingRequests = mutableMapOf<Int, PendingRequest>()
+    private val writeQueue = Channel<QueuedPacket>(capacity = 64)
+    private val closed = CompletableDeferred<Unit>()
+    private val shutdownStarted = AtomicBoolean(false)
+    private var writeErrorHandler: ((Throwable) -> Unit)? = null
+
+    init {
+        initialize(parserMap)
+    }
+
+    private fun initialize(parserMap: ParserMap) {
+        this.parserMap.putAll(parserMap)
+        this.parserMap[typeNameOf<HeartBeat>()] = { HeartBeat.parseFrom(it) }
+        isAlive.set(true)
+        scope.launch { writeLoop() }
+    }
+
+    fun isAlive(): Boolean = isAlive.get()
+
+    fun setWriteErrorHandler(fn: (Throwable) -> Unit) {
+        rwLock.write { writeErrorHandler = fn }
+    }
+
+    fun nextNonce(): Int = nonce.incrementAndGet()
+
+    fun shutdown() {
+        if (!shutdownStarted.compareAndSet(false, true)) return
+        isAlive.set(false)
+        writeQueue.close()
+        closed.complete(Unit)
+
+        val pending = rwLock.write {
+            val snapshot = pendingRequests.values.toList()
+            pendingRequests.clear()
+            snapshot
+        }
+        pending.forEach { it.errCh.trySend(NotConnectedException()) }
+    }
+
+    fun close() {
+        shutdown()
+        transport.close()
+    }
+
+    suspend fun queuePacket(base: PacketBase) {
+        if (!isAlive()) throw NotConnectedException()
+        val item = QueuedPacket(base)
+        try {
+            select<Unit> {
+                writeQueue.onSend(item) {}
+                closed.onAwait { throw NotConnectedException() }
+            }
+        } catch (e: ClosedSendChannelException) {
+            throw NotConnectedException()
+        }
+
+        val error = select {
+            item.done.onAwait { it }
+            closed.onAwait { NotConnectedException() }
+        }
+        if (error != null) throw error
+    }
+
+    suspend fun send(m: MessageLite) {
+        if (!isAlive()) throw NotConnectedException()
+        queuePacket(
+            PacketBase.newBuilder()
+                .setTypeName(typeNameOf(m))
+                .setNonce(nextNonce())
+                .setData(m.toByteString())
+                .build(),
+        )
+    }
+
+    suspend fun sendRequest(
+        req: MessageLite,
+        resTypeName: String,
+        timeoutMs: Long = 30_000L,
+    ): MessageLite {
+        if (!isAlive()) throw NotConnectedException()
+        val requestNonce = nextNonce()
+        val pending = PendingRequest(expectedTypeName = resTypeName)
+
+        rwLock.write { pendingRequests[requestNonce] = pending }
+
+        try {
+            queuePacket(
+                PacketBase.newBuilder()
+                    .setTypeName(typeNameOf(req))
+                    .setNonce(requestNonce)
+                    .setData(req.toByteString())
+                    .build(),
+            )
+        } catch (e: Throwable) {
+            removePending(requestNonce)
+            throw e
+        }
+
+        return try {
+            withTimeout(if (timeoutMs > 0) timeoutMs else 30_000L) {
+                select {
+                    pending.ch.onReceive { it }
+                    pending.errCh.onReceive { throw it }
+                    closed.onAwait { throw NotConnectedException() }
+                }
+            }
+        } catch (e: kotlinx.coroutines.TimeoutCancellationException) {
+            removePending(requestNonce)
+            throw IllegalStateException("request timeout for nonce $requestNonce", e)
+        }
+    }
+
+    fun addListener(typeName: String, fn: (MessageLite) -> Unit) {
+        rwLock.write {
+            check(!reqHandlers.containsKey(typeName)) {
+                "type $typeName is already registered with addRequestListener"
+            }
+            handlers.getOrPut(typeName) { mutableListOf() }.add(fn)
+        }
+    }
+
+    fun removeListeners(typeName: String) {
+        rwLock.write { handlers.remove(typeName) }
+    }
+
+    fun addRequestListener(typeName: String, fn: RequestHandler) {
+        rwLock.write {
+            check(handlers[typeName].isNullOrEmpty()) {
+                "type $typeName is already registered with addListener"
+            }
+            check(!reqHandlers.containsKey(typeName)) {
+                "type $typeName is already registered with addRequestListener"
+            }
+            reqHandlers[typeName] = fn
+        }
+    }
+
+    fun onReceivedData(
+        typeName: String,
+        data: ByteArray,
+        incomingNonce: Int = 0,
+        responseNonce: Int = 0,
+    ) {
+        if (responseNonce > 0) {
+            handleResponse(typeName, data, responseNonce)
+            return
+        }
+
+        val reqHandler: RequestHandler?
+        val listeners: List<(MessageLite) -> Unit>
+        rwLock.read {
+            reqHandler = reqHandlers[typeName]
+            listeners = handlers[typeName]?.toList().orEmpty()
+        }
+
+        if (reqHandler != null) {
+            val msg = runCatching { parse(typeName, data) }.getOrNull() ?: return
+            scope.launch { reqHandler(msg, incomingNonce) }
+            return
+        }
+
+        if (listeners.isEmpty()) return
+        val msg = runCatching { parse(typeName, data) }.getOrNull() ?: return
+        listeners.forEach { it(msg) }
+    }
+
+    private suspend fun writeLoop() {
+        for (item in writeQueue) {
+            val error = runCatching { transport.writePacket(item.base) }.exceptionOrNull()
+            item.done.complete(error)
+            if (error != null) {
+                val handler = rwLock.read { writeErrorHandler }
+                handler?.invoke(error)
+            }
+        }
+    }
+
+    private fun handleResponse(
+        typeName: String,
+        data: ByteArray,
+        responseNonce: Int,
+    ) {
+        val pending = removePending(responseNonce) ?: return
+        if (typeName != pending.expectedTypeName) {
+            pending.errCh.trySend(
+                IllegalStateException(
+                    "response type mismatch for nonce $responseNonce: " +
+                        "expected ${pending.expectedTypeName}, got $typeName",
+                ),
+            )
+            return
+        }
+        val msg = runCatching { parse(typeName, data) }
+        msg.onSuccess { pending.ch.trySend(it) }
+            .onFailure { pending.errCh.trySend(it) }
+    }
+
+    internal fun parse(typeName: String, data: ByteArray): MessageLite {
+        val parser = parserMap[typeName]
+            ?: throw IllegalStateException("protobuf parser is not registered for type $typeName")
+        return parser(data)
+    }
+
+    private fun removePending(nonce: Int): PendingRequest? =
+        rwLock.write { pendingRequests.remove(nonce) }
+}
+
+inline fun <reified T : Message> addListenerTyped(
+    communicator: Communicator,
+    noinline fn: (T) -> Unit,
+) {
+    val typeName = typeNameOf<T>()
+    communicator.addListener(typeName) { message ->
+        val typed = message as? T
+            ?: throw IllegalStateException("received ${message::class} for listener $typeName")
+        fn(typed)
+    }
+}
+
+inline fun <reified Req : Message, reified Res : Message> addRequestListenerTyped(
+    communicator: Communicator,
+    noinline fn: suspend (Req) -> Res,
+) {
+    val reqTypeName = typeNameOf<Req>()
+    communicator.addRequestListener(reqTypeName) { message, requestNonce ->
+        val req = message as? Req
+        if (req != null) {
+            val res = fn(req)
+            if (communicator.isAlive()) {
+                communicator.queuePacket(
+                    PacketBase.newBuilder()
+                        .setTypeName(typeNameOf(res))
+                        .setNonce(communicator.nextNonce())
+                        .setResponseNonce(requestNonce)
+                        .setData(res.toByteString())
+                        .build(),
+                )
+            }
+        }
+    }
+}
+
+suspend inline fun <reified Req : Message, reified Res : Message> sendRequestTyped(
+    communicator: Communicator,
+    req: Req,
+    timeoutMs: Long = 30_000L,
+): Res {
+    val msg = communicator.sendRequest(req, typeNameOf<Res>(), timeoutMs)
+    return msg as? Res
+        ?: throw IllegalStateException("received ${msg::class}, expected ${Res::class}")
+}
--- a/kotlin/src/main/kotlin/com/tokilabs/toki_socket/HeartbeatTimer.kt
+++ b/kotlin/src/main/kotlin/com/tokilabs/toki_socket/HeartbeatTimer.kt
@ -0,0 +1,31 @@
+package com.tokilabs.toki_socket
+
+import kotlinx.coroutines.CoroutineScope
+import kotlinx.coroutines.Job
+import kotlinx.coroutines.delay
+import kotlinx.coroutines.launch
+
+class HeartbeatTimer(
+    private val scope: CoroutineScope,
+    private val delayMs: Long,
+    private val callback: suspend () -> Unit,
+) {
+    private var job: Job? = null
+
+    init {
+        reset()
+    }
+
+    fun reset(delayMs: Long = this.delayMs) {
+        job?.cancel()
+        job = scope.launch {
+            delay(delayMs)
+            callback()
+        }
+    }
+
+    fun stop() {
+        job?.cancel()
+        job = null
+    }
+}
--- a/kotlin/src/main/kotlin/com/tokilabs/toki_socket/TcpClient.kt
+++ b/kotlin/src/main/kotlin/com/tokilabs/toki_socket/TcpClient.kt
@ -0,0 +1,129 @@
+package com.tokilabs.toki_socket
+
+import com.tokilabs.toki_socket.packets.HeartBeat
+import com.tokilabs.toki_socket.packets.PacketBase
+import kotlinx.coroutines.Dispatchers
+import kotlinx.coroutines.launch
+import kotlinx.coroutines.runBlocking
+import kotlinx.coroutines.sync.Mutex
+import kotlinx.coroutines.sync.withLock
+import kotlinx.coroutines.withContext
+import java.io.DataInputStream
+import java.io.IOException
+import java.net.InetSocketAddress
+import java.net.Socket
+import java.nio.ByteBuffer
+
+class TcpClient private constructor(
+    private val socket: Socket,
+    intervalSec: Int,
+    waitSec: Int,
+    parserMap: ParserMap,
+) : BaseClient<TcpClient>(
+    intervalSec = intervalSec,
+    waitSec = waitSec,
+    doClose = { socket.close() },
+),
+    Transport {
+    override val self: TcpClient
+        get() = this
+
+    override val communicator: Communicator = Communicator(this, parserMap, scope)
+    private val writeMutex = Mutex()
+
+    init {
+        communicator.setWriteErrorHandler { onDisconnected() }
+        communicator.addListener(typeNameOf<HeartBeat>()) { onHeartBeat() }
+        readLoop()
+        sendHeartBeat()
+    }
+
+    override suspend fun writePacket(base: PacketBase) {
+        val bytes = base.toByteArray()
+        if (bytes.size > MAX_PACKET_SIZE) {
+            throw IOException("packet size ${bytes.size} exceeds max $MAX_PACKET_SIZE")
+        }
+        val header = ByteBuffer.allocate(4).putInt(bytes.size).array()
+        writeMutex.withLock {
+            withContext(Dispatchers.IO) {
+                val output = socket.getOutputStream()
+                output.write(header)
+                output.write(bytes)
+                output.flush()
+            }
+        }
+    }
+
+    private fun readLoop() {
+        scope.launch(Dispatchers.IO) {
+            val input = DataInputStream(socket.getInputStream())
+            while (communicator.isAlive()) {
+                try {
+                    val length = input.readInt()
+                    if (length == 0) continue
+                    if (length < 0 || length > MAX_PACKET_SIZE) {
+                        onDisconnected()
+                        return@launch
+                    }
+                    val bytes = ByteArray(length)
+                    input.readFully(bytes)
+                    val base = PacketBase.parseFrom(bytes)
+                    communicator.onReceivedData(
+                        base.typeName,
+                        base.data.toByteArray(),
+                        base.nonce,
+                        base.responseNonce,
+                    )
+                    sendHeartBeat()
+                } catch (_: Exception) {
+                    onDisconnected()
+                    return@launch
+                }
+            }
+        }
+    }
+
+    suspend fun send(message: com.google.protobuf.MessageLite) {
+        communicator.send(message)
+    }
+
+    companion object {
+        const val MAX_PACKET_SIZE: Int = 64 * 1024 * 1024
+
+        fun fromSocket(
+            socket: Socket,
+            intervalSec: Int = 30,
+            waitSec: Int = 10,
+            parserMap: ParserMap,
+        ): TcpClient = TcpClient(socket, intervalSec, waitSec, parserMap)
+    }
+}
+
+fun dialTcp(
+    host: String,
+    port: Int,
+    intervalSec: Int = 30,
+    waitSec: Int = 10,
+    parserMap: ParserMap,
+): TcpClient {
+    val socket = Socket()
+    socket.connect(InetSocketAddress(host, port))
+    return TcpClient.fromSocket(socket, intervalSec, waitSec, parserMap)
+}
+
+@Suppress("FunctionName")
+fun DialTcp(
+    host: String,
+    port: Int,
+    intervalSec: Int = 30,
+    waitSec: Int = 10,
+    parserMap: ParserMap,
+): TcpClient = dialTcp(host, port, intervalSec, waitSec, parserMap)
+
+fun TcpClient.closeBlocking() {
+    close()
+}
+
+fun TcpClient.sendBlocking(message: com.google.protobuf.MessageLite) {
+    runBlocking { send(message) }
+}
--- a/kotlin/src/main/kotlin/com/tokilabs/toki_socket/TcpServer.kt
+++ b/kotlin/src/main/kotlin/com/tokilabs/toki_socket/TcpServer.kt
@ -0,0 +1,77 @@
+package com.tokilabs.toki_socket
+
+import com.google.protobuf.MessageLite
+import kotlinx.coroutines.CoroutineScope
+import kotlinx.coroutines.Dispatchers
+import kotlinx.coroutines.SupervisorJob
+import kotlinx.coroutines.cancel
+import kotlinx.coroutines.launch
+import kotlinx.coroutines.runBlocking
+import java.net.InetSocketAddress
+import java.net.ServerSocket
+import java.net.SocketException
+import java.util.concurrent.CopyOnWriteArrayList
+import java.util.concurrent.atomic.AtomicBoolean
+
+class TcpServer(
+    private val host: String,
+    private val port: Int,
+    private val newClient: (java.net.Socket) -> TcpClient,
+) {
+    private val scope = CoroutineScope(SupervisorJob() + Dispatchers.IO)
+    private val clients = CopyOnWriteArrayList<TcpClient>()
+    private val started = AtomicBoolean(false)
+    private var serverSocket: ServerSocket? = null
+
+    var onClientConnected: (TcpClient) -> Unit = {}
+
+    fun started(): Boolean = started.get()
+
+    fun clients(): List<TcpClient> = clients.toList()
+
+    fun start() {
+        if (!started.compareAndSet(false, true)) return
+        val server = ServerSocket()
+        server.reuseAddress = true
+        server.bind(InetSocketAddress(host, port))
+        serverSocket = server
+        scope.launch(Dispatchers.IO) {
+            acceptLoop(server)
+        }
+    }
+
+    fun stop() {
+        if (!started.compareAndSet(true, false)) return
+        runCatching { serverSocket?.close() }
+        val snapshot = clients.toList()
+        clients.clear()
+        snapshot.forEach { it.close() }
+        scope.cancel()
+    }
+
+    suspend fun broadcast(message: MessageLite) {
+        clients().forEach { client ->
+            client.communicator.send(message)
+        }
+    }
+
+    private fun acceptLoop(server: ServerSocket) {
+        while (started.get()) {
+            try {
+                val socket = server.accept()
+                val client = newClient(socket)
+                client.addDisconnectListener { clients.remove(it) }
+                clients.add(client)
+                onClientConnected(client)
+            } catch (_: SocketException) {
+                return
+            } catch (_: Exception) {
+                if (!started.get()) return
+            }
+        }
+    }
+}
+
+fun TcpServer.broadcastBlocking(message: MessageLite) {
+    runBlocking { broadcast(message) }
+}
--- a/kotlin/src/main/kotlin/com/tokilabs/toki_socket/WsClient.kt
+++ b/kotlin/src/main/kotlin/com/tokilabs/toki_socket/WsClient.kt
@ -0,0 +1,228 @@
+package com.tokilabs.toki_socket
+
+import com.tokilabs.toki_socket.packets.HeartBeat
+import com.tokilabs.toki_socket.packets.PacketBase
+import kotlinx.coroutines.runBlocking
+import okhttp3.OkHttpClient
+import okhttp3.Request
+import okhttp3.Response
+import okhttp3.WebSocketListener
+import okio.ByteString
+import org.java_websocket.WebSocket
+import java.io.IOException
+import java.security.KeyStore
+import java.util.concurrent.CountDownLatch
+import java.util.concurrent.TimeUnit
+import java.util.concurrent.atomic.AtomicReference
+import javax.net.ssl.SSLContext
+import javax.net.ssl.TrustManagerFactory
+import javax.net.ssl.X509TrustManager
+
+class WsClient internal constructor(
+    private val connection: WsConnection,
+    intervalSec: Int,
+    waitSec: Int,
+    parserMap: ParserMap,
+) : BaseClient<WsClient>(
+    intervalSec = intervalSec,
+    waitSec = waitSec,
+    doClose = { connection.close() },
+),
+    Transport {
+    override val self: WsClient
+        get() = this
+
+    override val communicator: Communicator = Communicator(this, parserMap, scope)
+
+    init {
+        communicator.setWriteErrorHandler { onDisconnected() }
+        communicator.addListener(typeNameOf<HeartBeat>()) { onHeartBeat() }
+        sendHeartBeat()
+    }
+
+    override suspend fun writePacket(base: PacketBase) {
+        val bytes = base.toByteArray()
+        if (!connection.send(bytes)) {
+            throw IOException("websocket send failed")
+        }
+    }
+
+    internal fun receiveBytes(bytes: ByteArray) {
+        try {
+            val base = PacketBase.parseFrom(bytes)
+            communicator.onReceivedData(
+                base.typeName,
+                base.data.toByteArray(),
+                base.nonce,
+                base.responseNonce,
+            )
+            sendHeartBeat()
+        } catch (_: Exception) {
+            onDisconnected()
+        }
+    }
+
+    internal fun handleFailure() {
+        onDisconnected()
+    }
+
+    suspend fun send(message: com.google.protobuf.MessageLite) {
+        communicator.send(message)
+    }
+
+    companion object {
+        fun forServer(
+            conn: WebSocket,
+            intervalSec: Int,
+            waitSec: Int,
+            parserMap: ParserMap,
+        ): WsClient = WsClient(JavaWebSocketConnection(conn), intervalSec, waitSec, parserMap)
+    }
+}
+
+internal interface WsConnection {
+    fun send(bytes: ByteArray): Boolean
+
+    fun close()
+}
+
+private class JavaWebSocketConnection(
+    private val conn: WebSocket,
+) : WsConnection {
+    override fun send(bytes: ByteArray): Boolean =
+        runCatching {
+            conn.send(bytes)
+            true
+        }.getOrElse { false }
+
+    override fun close() {
+        runCatching { conn.close(1000) }
+    }
+}
+
+private class OkHttpWsConnection(
+    private val client: OkHttpClient,
+) : WsConnection {
+    private val socketRef = AtomicReference<okhttp3.WebSocket?>()
+
+    fun setSocket(ws: okhttp3.WebSocket) {
+        socketRef.set(ws)
+    }
+
+    override fun send(bytes: ByteArray): Boolean =
+        socketRef.get()?.send(ByteString.of(*bytes)) ?: false
+
+    override fun close() {
+        runCatching { socketRef.get()?.close(1000, null) }
+        client.dispatcher.executorService.shutdown()
+    }
+}
+
+fun dialWs(
+    host: String,
+    port: Int,
+    path: String,
+    intervalSec: Int = 30,
+    waitSec: Int = 10,
+    parserMap: ParserMap,
+): WsClient = dialWsUrl("ws://$host:$port$path", null, intervalSec, waitSec, parserMap)
+
+fun dialWss(
+    host: String,
+    port: Int,
+    path: String,
+    sslContext: SSLContext?,
+    intervalSec: Int = 30,
+    waitSec: Int = 10,
+    parserMap: ParserMap,
+): WsClient = dialWsUrl("wss://$host:$port$path", sslContext, intervalSec, waitSec, parserMap)
+
+private fun dialWsUrl(
+    url: String,
+    sslContext: SSLContext?,
+    intervalSec: Int,
+    waitSec: Int,
+    parserMap: ParserMap,
+): WsClient {
+    val builder = OkHttpClient.Builder()
+    if (sslContext != null) {
+        builder.sslSocketFactory(sslContext.socketFactory, defaultTrustManager())
+    }
+    val okHttpClient = builder.build()
+    val connection = OkHttpWsConnection(okHttpClient)
+    val opened = CountDownLatch(1)
+    val failed = AtomicReference<Throwable?>()
+    var client: WsClient? = null
+    val listener = object : WebSocketListener() {
+        override fun onOpen(webSocket: okhttp3.WebSocket, response: Response) {
+            connection.setSocket(webSocket)
+            opened.countDown()
+        }
+
+        override fun onMessage(webSocket: okhttp3.WebSocket, bytes: ByteString) {
+            client?.receiveBytes(bytes.toByteArray())
+        }
+
+        override fun onClosing(webSocket: okhttp3.WebSocket, code: Int, reason: String) {
+            webSocket.close(code, reason)
+            client?.handleFailure()
+        }
+
+        override fun onClosed(webSocket: okhttp3.WebSocket, code: Int, reason: String) {
+            client?.handleFailure()
+        }
+
+        override fun onFailure(webSocket: okhttp3.WebSocket, t: Throwable, response: Response?) {
+            failed.set(t)
+            opened.countDown()
+            client?.handleFailure()
+        }
+    }
+
+    client = WsClient(connection, intervalSec, waitSec, parserMap)
+    val ws = okHttpClient.newWebSocket(Request.Builder().url(url).build(), listener)
+    connection.setSocket(ws)
+    if (!opened.await(5, TimeUnit.SECONDS)) {
+        client.close()
+        throw IOException("websocket open timed out")
+    }
+    failed.get()?.let {
+        client.close()
+        throw IOException("websocket open failed", it)
+    }
+    return client
+}
+
+private fun defaultTrustManager(): X509TrustManager {
+    val factory = TrustManagerFactory.getInstance(TrustManagerFactory.getDefaultAlgorithm())
+    factory.init(null as KeyStore?)
+    return factory.trustManagers
+        .filterIsInstance<X509TrustManager>()
+        .singleOrNull()
+        ?: throw IllegalStateException("expected exactly one default X509TrustManager")
+}
+
+@Suppress("FunctionName")
+fun DialWs(
+    host: String,
+    port: Int,
+    path: String,
+    intervalSec: Int = 30,
+    waitSec: Int = 10,
+    parserMap: ParserMap,
+): WsClient = dialWs(host, port, path, intervalSec, waitSec, parserMap)
+
+@Suppress("FunctionName")
+fun DialWss(
+    host: String,
+    port: Int,
+    path: String,
+    sslContext: SSLContext?,
+    intervalSec: Int = 30,
+    waitSec: Int = 10,
+    parserMap: ParserMap,
+): WsClient = dialWss(host, port, path, sslContext, intervalSec, waitSec, parserMap)
+
+fun WsClient.sendBlocking(message: com.google.protobuf.MessageLite) {
+    runBlocking { send(message) }
+}
--- a/kotlin/src/main/kotlin/com/tokilabs/toki_socket/WsServer.kt
+++ b/kotlin/src/main/kotlin/com/tokilabs/toki_socket/WsServer.kt
@ -0,0 +1,93 @@
+package com.tokilabs.toki_socket
+
+import com.google.protobuf.MessageLite
+import kotlinx.coroutines.runBlocking
+import org.java_websocket.WebSocket
+import org.java_websocket.handshake.ClientHandshake
+import org.java_websocket.server.WebSocketServer
+import java.net.InetSocketAddress
+import java.nio.ByteBuffer
+import java.util.concurrent.ConcurrentHashMap
+import java.util.concurrent.CopyOnWriteArrayList
+import java.util.concurrent.atomic.AtomicBoolean
+
+class WsServer(
+    host: String,
+    port: Int,
+    private val path: String = "/",
+    private val newClient: (WebSocket) -> WsClient,
+) : WebSocketServer(InetSocketAddress(host, port)) {
+    private val clientByConn = ConcurrentHashMap<WebSocket, WsClient>()
+    private val clients = CopyOnWriteArrayList<WsClient>()
+    private val startedFlag = AtomicBoolean(false)
+
+    var onClientConnected: (WsClient) -> Unit = {}
+
+    fun started(): Boolean = startedFlag.get()
+
+    fun clients(): List<WsClient> = clients.toList()
+
+    override fun start() {
+        startedFlag.set(true)
+        super.start()
+    }
+
+    override fun stop() {
+        if (!startedFlag.compareAndSet(true, false)) return
+        val snapshot = clients.toList()
+        clients.clear()
+        snapshot.forEach { it.close() }
+        runCatching { super.stop(1000) }
+    }
+
+    suspend fun broadcast(message: MessageLite) {
+        clients().forEach { client ->
+            client.communicator.send(message)
+        }
+    }
+
+    override fun onOpen(conn: WebSocket, handshake: ClientHandshake) {
+        if (handshake.resourceDescriptor != path) {
+            conn.close(1008, "unexpected path")
+            return
+        }
+        val client = newClient(conn)
+        client.addDisconnectListener {
+            clients.remove(it)
+            clientByConn.remove(conn)
+        }
+        clientByConn[conn] = client
+        clients.add(client)
+        onClientConnected(client)
+    }
+
+    override fun onMessage(conn: WebSocket, message: String) {
+    }
+
+    override fun onMessage(conn: WebSocket, message: ByteBuffer) {
+        val bytes = ByteArray(message.remaining())
+        message.get(bytes)
+        clientByConn[conn]?.receiveBytes(bytes)
+    }
+
+    override fun onClose(
+        conn: WebSocket,
+        code: Int,
+        reason: String,
+        remote: Boolean,
+    ) {
+        clientByConn.remove(conn)?.handleFailure()
+    }
+
+    override fun onError(conn: WebSocket?, ex: Exception) {
+        if (conn == null) return
+        clientByConn[conn]?.handleFailure()
+    }
+
+    override fun onStart() {
+    }
+}
+
+fun WsServer.broadcastBlocking(message: MessageLite) {
+    runBlocking { broadcast(message) }
+}
--- a/kotlin/src/main/proto/message_common.proto
+++ b/kotlin/src/main/proto/message_common.proto
@ -0,0 +1,19 @@
+syntax = "proto3";
+
+option java_package = "com.tokilabs.toki_socket.packets";
+option java_outer_classname = "MessageCommonProto";
+option java_multiple_files = true;
+
+message PacketBase {
+  string typeName = 1;
+  int32 nonce = 2;
+  bytes data = 3;
+  int32 responseNonce = 4;
+}
+
+message HeartBeat {}
+
+message TestData {
+  int32 index = 1;
+  string message = 2;
+}
--- a/kotlin/src/test/kotlin/com/tokilabs/toki_socket/CommunicatorTest.kt
+++ b/kotlin/src/test/kotlin/com/tokilabs/toki_socket/CommunicatorTest.kt
@ -0,0 +1,95 @@
+package com.tokilabs.toki_socket
+
+import com.tokilabs.toki_socket.packets.HeartBeat
+import com.tokilabs.toki_socket.packets.PacketBase
+import com.tokilabs.toki_socket.packets.TestData
+import kotlinx.coroutines.CoroutineScope
+import kotlinx.coroutines.Dispatchers
+import kotlinx.coroutines.SupervisorJob
+import kotlinx.coroutines.async
+import kotlinx.coroutines.delay
+import kotlinx.coroutines.test.runTest
+import java.util.Collections
+import kotlin.test.Test
+import kotlin.test.assertEquals
+import kotlin.test.assertFailsWith
+import kotlin.test.assertTrue
+
+private class FakeTransport : Transport {
+    val packets: MutableList<PacketBase> = Collections.synchronizedList(mutableListOf())
+
+    override suspend fun writePacket(base: PacketBase) {
+        packets.add(base)
+    }
+
+    override fun close() {
+    }
+}
+
+class CommunicatorTest {
+    @Test
+    fun testSendRequestTimeout() = runTest {
+        val transport = FakeTransport()
+        val communicator = Communicator(transport, testParserMap(), CoroutineScope(SupervisorJob() + Dispatchers.Default))
+
+        val err = assertFailsWith<IllegalStateException> {
+            sendRequestTyped<TestData, TestData>(
+                communicator,
+                TestData.newBuilder().setIndex(1).setMessage("no response").build(),
+                timeoutMs = 25,
+            )
+        }
+        assertTrue(err.message!!.contains("timeout"))
+        assertEquals(1, transport.packets.size)
+        communicator.close()
+    }
+
+    @Test
+    fun testSendRequestTypeMismatch() = runTest {
+        val transport = FakeTransport()
+        val communicator = Communicator(transport, testParserMap(), CoroutineScope(SupervisorJob() + Dispatchers.Default))
+
+        val result = async {
+            assertFailsWith<IllegalStateException> {
+                sendRequestTyped<TestData, TestData>(
+                    communicator,
+                    TestData.newBuilder().setIndex(1).setMessage("hello").build(),
+                    timeoutMs = 1_000,
+                )
+            }
+        }
+        while (transport.packets.isEmpty()) delay(1)
+        val requestNonce = transport.packets.single().nonce
+        communicator.onReceivedData(
+            typeNameOf<HeartBeat>(),
+            HeartBeat.getDefaultInstance().toByteArray(),
+            responseNonce = requestNonce,
+        )
+        assertTrue(result.await().message!!.contains("response type mismatch"))
+        communicator.close()
+    }
+
+    @Test
+    fun testListenerAndRequestListenerConflict() = runTest {
+        val transport = FakeTransport()
+        val communicator = Communicator(transport, testParserMap(), CoroutineScope(SupervisorJob() + Dispatchers.Default))
+
+        addListenerTyped<TestData>(communicator) {}
+        assertFailsWith<IllegalStateException> {
+            addRequestListenerTyped<TestData, TestData>(communicator) { it }
+        }
+        communicator.close()
+    }
+
+    @Test
+    fun testSendFireAndForget() = runTest {
+        val transport = FakeTransport()
+        val communicator = Communicator(transport, testParserMap(), CoroutineScope(SupervisorJob() + Dispatchers.Default))
+
+        communicator.send(TestData.newBuilder().setIndex(7).setMessage("fire").build())
+
+        assertEquals(1, transport.packets.size)
+        assertEquals(typeNameOf<TestData>(), transport.packets.single().typeName)
+        communicator.close()
+    }
+}
--- a/kotlin/src/test/kotlin/com/tokilabs/toki_socket/HeartbeatTest.kt
+++ b/kotlin/src/test/kotlin/com/tokilabs/toki_socket/HeartbeatTest.kt
@ -0,0 +1,107 @@
+package com.tokilabs.toki_socket
+
+import com.tokilabs.toki_socket.packets.HeartBeat
+import com.tokilabs.toki_socket.packets.PacketBase
+import kotlinx.coroutines.delay
+import kotlinx.coroutines.runBlocking
+import java.util.Collections
+import kotlin.test.Test
+import kotlin.test.assertTrue
+
+private class HeartbeatTransport : Transport {
+    val packets: MutableList<PacketBase> = Collections.synchronizedList(mutableListOf())
+
+    override suspend fun writePacket(base: PacketBase) {
+        packets.add(base)
+    }
+
+    override fun close() {
+    }
+}
+
+private class HeartbeatClient(
+    private val transport: HeartbeatTransport,
+    intervalSec: Int,
+    waitSec: Int,
+) : BaseClient<HeartbeatClient>(
+    intervalSec = intervalSec,
+    waitSec = waitSec,
+    doClose = { transport.close() },
+) {
+    override val self: HeartbeatClient
+        get() = this
+
+    override val communicator = Communicator(transport, testParserMap(), scope)
+
+    init {
+        communicator.addListener(typeNameOf<HeartBeat>()) { onHeartBeat() }
+    }
+}
+
+class HeartbeatTest {
+    @Test
+    fun testHeartbeatSentAfterInactivity() = runBlocking {
+        val transport = HeartbeatTransport()
+        val client = HeartbeatClient(transport, 1, 1)
+
+        client.sendHeartBeat()
+        delay(1_100)
+
+        assertTrue(transport.packets.any { it.typeName == typeNameOf<HeartBeat>() })
+        client.close()
+    }
+
+    @Test
+    fun testHeartbeatDisconnectOnNoResponse() = runBlocking {
+        val transport = HeartbeatTransport()
+        val client = HeartbeatClient(transport, 1, 1)
+        var disconnected = false
+        client.addDisconnectListener { disconnected = true }
+
+        client.sendHeartBeat()
+        delay(2_300)
+
+        assertTrue(disconnected)
+        assertTrue(!client.communicator.isAlive())
+    }
+
+    @Test
+    fun testHeartbeatTimerResetBySendHeartBeat() = runBlocking {
+        val transport = HeartbeatTransport()
+        val client = HeartbeatClient(transport, 1, 1)
+
+        client.sendHeartBeat()
+        delay(700)
+        client.sendHeartBeat()
+        delay(500)
+        assertTrue(transport.packets.none { it.typeName == typeNameOf<HeartBeat>() })
+        delay(700)
+        assertTrue(transport.packets.any { it.typeName == typeNameOf<HeartBeat>() })
+        client.close()
+    }
+
+    @Test
+    fun testHeartbeatTimerResetOnReceivedData() = runBlocking {
+        val transport = HeartbeatTransport()
+        val client = HeartbeatClient(transport, 1, 1)
+        var received = false
+        client.communicator.addListener(typeNameOf(testData())) {
+            received = true
+        }
+
+        client.sendHeartBeat()
+        delay(700)
+        client.communicator.onReceivedData(
+            typeNameOf(testData()),
+            testData().toByteArray(),
+            incomingNonce = 1,
+        )
+        assertTrue(received)
+        client.sendHeartBeat()
+        delay(500)
+        assertTrue(transport.packets.none { it.typeName == typeNameOf<HeartBeat>() })
+        delay(700)
+        assertTrue(transport.packets.any { it.typeName == typeNameOf<HeartBeat>() })
+        client.close()
+    }
+}
--- a/kotlin/src/test/kotlin/com/tokilabs/toki_socket/HeartbeatTimerTest.kt
+++ b/kotlin/src/test/kotlin/com/tokilabs/toki_socket/HeartbeatTimerTest.kt
@ -0,0 +1,49 @@
+package com.tokilabs.toki_socket
+
+import kotlinx.coroutines.CompletableDeferred
+import kotlinx.coroutines.test.runTest
+import kotlin.test.Test
+import kotlin.test.assertFalse
+import kotlin.test.assertTrue
+
+class HeartbeatTimerTest {
+    @Test
+    fun testCallbackFires() = runTest {
+        var fired = false
+        HeartbeatTimer(this, 100) {
+            fired = true
+        }
+
+        testScheduler.advanceTimeBy(101)
+
+        assertTrue(fired)
+    }
+
+    @Test
+    fun testStopPreventsCallback() = runTest {
+        var fired = false
+        val timer = HeartbeatTimer(this, 100) {
+            fired = true
+        }
+        timer.stop()
+
+        testScheduler.advanceTimeBy(150)
+
+        assertFalse(fired)
+    }
+
+    @Test
+    fun testResetRestartsTimer() = runTest {
+        val fired = CompletableDeferred<Unit>()
+        val timer = HeartbeatTimer(this, 100) {
+            fired.complete(Unit)
+        }
+
+        testScheduler.advanceTimeBy(80)
+        timer.reset()
+        testScheduler.advanceTimeBy(80)
+        assertFalse(fired.isCompleted)
+        testScheduler.advanceTimeBy(21)
+        assertTrue(fired.isCompleted)
+    }
+}
--- a/kotlin/src/test/kotlin/com/tokilabs/toki_socket/TcpTest.kt
+++ b/kotlin/src/test/kotlin/com/tokilabs/toki_socket/TcpTest.kt
@ -0,0 +1,114 @@
+package com.tokilabs.toki_socket
+
+import com.tokilabs.toki_socket.packets.TestData
+import kotlinx.coroutines.CompletableDeferred
+import kotlinx.coroutines.Dispatchers
+import kotlinx.coroutines.async
+import kotlinx.coroutines.runBlocking
+import java.net.Socket
+import kotlin.test.Test
+import kotlin.test.assertEquals
+import kotlin.test.assertFalse
+
+class TcpTest {
+    @Test
+    fun testTcpSendReceive() = runBlocking {
+        val port = freePort()
+        val received = CompletableDeferred<TestData>()
+        val server = TcpServer("127.0.0.1", port) { socket ->
+            TcpClient.fromSocket(socket, 0, 0, testParserMap())
+        }
+        server.onClientConnected = { client ->
+            addListenerTyped<TestData>(client.communicator) { received.complete(it) }
+        }
+        server.start()
+        val client = DialTcp("127.0.0.1", port, 0, 0, testParserMap())
+
+        client.send(TestData.newBuilder().setIndex(42).setMessage("hello toki-socket").build())
+
+        assertEquals(42, received.await().index)
+        client.close()
+        server.stop()
+    }
+
+    @Test
+    fun testTcpRequestResponse() = runBlocking {
+        val port = freePort()
+        val server = TcpServer("127.0.0.1", port) { socket ->
+            TcpClient.fromSocket(socket, 0, 0, testParserMap())
+        }
+        server.onClientConnected = { client ->
+            addRequestListenerTyped<TestData, TestData>(client.communicator) { req ->
+                TestData.newBuilder()
+                    .setIndex(req.index * 2)
+                    .setMessage("echo: ${req.message}")
+                    .build()
+            }
+        }
+        server.start()
+        val client = DialTcp("127.0.0.1", port, 0, 0, testParserMap())
+
+        val res = sendRequestTyped<TestData, TestData>(
+            client.communicator,
+            TestData.newBuilder().setIndex(21).setMessage("hello").build(),
+            timeoutMs = 2_000,
+        )
+
+        assertEquals(42, res.index)
+        assertEquals("echo: hello", res.message)
+        client.close()
+        server.stop()
+    }
+
+    @Test
+    fun testTcpBroadcast() = runBlocking {
+        val port = freePort()
+        val server = TcpServer("127.0.0.1", port) { socket ->
+            TcpClient.fromSocket(socket, 0, 0, testParserMap())
+        }
+        server.start()
+        val client = DialTcp("127.0.0.1", port, 0, 0, testParserMap())
+        val received = CompletableDeferred<TestData>()
+        addListenerTyped<TestData>(client.communicator) { received.complete(it) }
+
+        waitForCondition(message = "client did not connect") { server.clients().size == 1 }
+        server.broadcast(TestData.newBuilder().setIndex(9).setMessage("broadcast").build())
+
+        assertEquals("broadcast", received.await().message)
+        client.close()
+        server.stop()
+    }
+
+    @Test
+    fun testTcpServerStopDisconnectsClients() = runBlocking {
+        val port = freePort()
+        val server = TcpServer("127.0.0.1", port) { socket ->
+            TcpClient.fromSocket(socket, 0, 0, testParserMap())
+        }
+        server.start()
+        val client = DialTcp("127.0.0.1", port, 0, 0, testParserMap())
+        val disconnected = CompletableDeferred<Unit>()
+        client.addDisconnectListener { disconnected.complete(Unit) }
+
+        waitForCondition(message = "client did not connect") { server.clients().size == 1 }
+        server.stop()
+
+        disconnected.await()
+        assertFalse(client.communicator.isAlive())
+    }
+
+    @Test
+    fun testTcpClientCloseIdempotent() = runBlocking {
+        val serverSocket = java.net.ServerSocket(0)
+        val accept = async(Dispatchers.IO) { serverSocket.accept() }
+        val socket = Socket("127.0.0.1", serverSocket.localPort)
+        val peer = accept.await()
+        val client = TcpClient.fromSocket(socket, 0, 0, testParserMap())
+
+        repeat(3) { client.close() }
+
+        assertFalse(client.communicator.isAlive())
+        peer.close()
+        serverSocket.close()
+    }
+}
--- a/kotlin/src/test/kotlin/com/tokilabs/toki_socket/TestHelpers.kt
+++ b/kotlin/src/test/kotlin/com/tokilabs/toki_socket/TestHelpers.kt
@ -0,0 +1,33 @@
+package com.tokilabs.toki_socket
+
+import com.tokilabs.toki_socket.packets.TestData
+import java.net.ServerSocket
+import kotlin.test.fail
+
+fun testParserMap(): ParserMap =
+    mapOf(
+        typeNameOf<TestData>() to { TestData.parseFrom(it) },
+    )
+
+fun testData(): TestData =
+    TestData.newBuilder()
+        .setIndex(1)
+        .setMessage("ping")
+        .build()
+
+fun freePort(): Int =
+    ServerSocket(0).use { it.localPort }
+
+suspend fun waitForCondition(
+    timeoutMs: Long = 2_000L,
+    intervalMs: Long = 10L,
+    message: String,
+    predicate: () -> Boolean,
+) {
+    val deadline = System.nanoTime() + timeoutMs * 1_000_000L
+    while (System.nanoTime() < deadline) {
+        if (predicate()) return
+        kotlinx.coroutines.delay(intervalMs)
+    }
+    fail(message)
+}
--- a/kotlin/src/test/kotlin/com/tokilabs/toki_socket/WsTest.kt
+++ b/kotlin/src/test/kotlin/com/tokilabs/toki_socket/WsTest.kt
@ -0,0 +1,101 @@
+package com.tokilabs.toki_socket
+
+import com.tokilabs.toki_socket.packets.TestData
+import kotlinx.coroutines.CompletableDeferred
+import kotlinx.coroutines.runBlocking
+import kotlin.test.Test
+import kotlin.test.assertEquals
+import kotlin.test.assertFalse
+
+class WsTest {
+    @Test
+    fun testWsSendReceive() = runBlocking {
+        val port = freePort()
+        val received = CompletableDeferred<TestData>()
+        val server = WsServer("127.0.0.1", port, "/") { conn ->
+            WsClient.forServer(conn, 0, 0, testParserMap())
+        }
+        server.onClientConnected = { client ->
+            addListenerTyped<TestData>(client.communicator) { received.complete(it) }
+        }
+        server.start()
+        val client = DialWs("127.0.0.1", port, "/", 0, 0, testParserMap())
+
+        client.send(TestData.newBuilder().setIndex(42).setMessage("hello toki-socket ws").build())
+
+        assertEquals(42, received.await().index)
+        client.close()
+        server.stop()
+    }
+
+    @Test
+    fun testWsRequestResponse() = runBlocking {
+        val port = freePort()
+        val server = WsServer("127.0.0.1", port, "/") { conn ->
+            WsClient.forServer(conn, 0, 0, testParserMap())
+        }
+        server.onClientConnected = { client ->
+            addRequestListenerTyped<TestData, TestData>(client.communicator) { req ->
+                TestData.newBuilder()
+                    .setIndex(req.index * 2)
+                    .setMessage("echo: ${req.message}")
+                    .build()
+            }
+        }
+        server.start()
+        val client = DialWs("127.0.0.1", port, "/", 0, 0, testParserMap())
+
+        val res = sendRequestTyped<TestData, TestData>(
+            client.communicator,
+            TestData.newBuilder().setIndex(21).setMessage("hello ws").build(),
+            timeoutMs = 2_000,
+        )
+
+        assertEquals(42, res.index)
+        assertEquals("echo: hello ws", res.message)
+        client.close()
+        server.stop()
+    }
+
+    @Test
+    fun testWsBroadcast() = runBlocking {
+        val port = freePort()
+        val server = WsServer("127.0.0.1", port, "/") { conn ->
+            WsClient.forServer(conn, 0, 0, testParserMap())
+        }
+        server.start()
+        val client1 = DialWs("127.0.0.1", port, "/", 0, 0, testParserMap())
+        val client2 = DialWs("127.0.0.1", port, "/", 0, 0, testParserMap())
+        val received1 = CompletableDeferred<TestData>()
+        val received2 = CompletableDeferred<TestData>()
+        addListenerTyped<TestData>(client1.communicator) { received1.complete(it) }
+        addListenerTyped<TestData>(client2.communicator) { received2.complete(it) }
+
+        waitForCondition(message = "clients did not connect") { server.clients().size == 2 }
+        server.broadcast(TestData.newBuilder().setIndex(9).setMessage("ws broadcast").build())
+
+        assertEquals("ws broadcast", received1.await().message)
+        assertEquals("ws broadcast", received2.await().message)
+        client1.close()
+        client2.close()
+        server.stop()
+    }
+
+    @Test
+    fun testWsServerStopDisconnectsClients() = runBlocking {
+        val port = freePort()
+        val server = WsServer("127.0.0.1", port, "/") { conn ->
+            WsClient.forServer(conn, 0, 0, testParserMap())
+        }
+        server.start()
+        val client = DialWs("127.0.0.1", port, "/", 0, 0, testParserMap())
+        val disconnected = CompletableDeferred<Unit>()
+        client.addDisconnectListener { disconnected.complete(Unit) }
+
+        waitForCondition(message = "client did not connect") { server.clients().size == 1 }
+        server.stop()
+
+        disconnected.await()
+        assertFalse(client.communicator.isAlive())
+    }
+}
--- a/skills/code-review/SKILL.md
+++ b/skills/code-review/SKILL.md
@ -1,6 +1,6 @@
 ---
 name: code-review
-description: Review completed implementation work in the current repository. Reads PLAN.md and CODE_REVIEW.md from the active task, reviews the actual changed source files, appends a verdict to CODE_REVIEW.md, then archives both files as .log. If Required or Suggested issues are found (FAIL or WARN), writes a new PLAN.md and CODE_REVIEW.md stub so the loop continues immediately. Nit-only findings may still PASS.
+description: Review completed implementation work in the current repository. Reads PLAN.md and CODE_REVIEW.md from the active task, reviews the actual changed source files, appends a verdict to CODE_REVIEW.md, then archives both files as .log. On PASS, writes complete.log summarising the full loop history. If Required or Suggested issues are found (FAIL or WARN), writes a new PLAN.md and CODE_REVIEW.md stub so the loop continues immediately. Nit-only findings may still PASS.
 ---

 # Code Review
@ -24,7 +24,8 @@ Directory states:
 | State | Meaning |
 |-------|---------|
 | `PLAN.md` + `CODE_REVIEW.md` | Ready for review |
-| Only `*.log` files | Task complete |
+| `complete.log` + `*.log` files | Task complete (PASS) |
+| Only `*.log` files (no `complete.log`) | Task terminated mid-loop or abandoned |

 The implementing agent never archives or deletes active files; archiving is this skill's responsibility.

@ -93,11 +94,20 @@ After archiving, neither active `.md` file remains unless Step 6 writes a follow

 ## Step 6 - Post-Review Actions

-For `PASS`, report:
+For `PASS`, write `tasks/{task_name}/complete.log` before reporting:
+
+Required fields in `complete.log`:
+- `완료 일시`: date completed.
+- `요약`: one-line task description and loop count.
+- `루프 이력`: table of plan/code_review log pairs with their verdict.
+- `최종 리뷰 요약`: bullet list of what was implemented.
+- `잔여 Nit`: any Nit-only findings recorded but not acted on (omit section if none).
+
+Then report:

 - Verdict.
 - Archive filenames.
- Task complete; only `.log` files remain.
+- `complete.log` written; task complete.

 For `WARN` or `FAIL`, write a new `PLAN.md` and `CODE_REVIEW.md` stub using the plan skill format:

@ -106,7 +116,75 @@ For `WARN` or `FAIL`, write a new `PLAN.md` and `CODE_REVIEW.md` stub using the
 - `FAIL`: one plan item per Required issue.
 - `WARN`: one grouped plan item for Suggested issues, plus related Nit issues if useful.
 - Each plan item needs problem, solution with before/after when non-trivial, checklist, test decision, intermediate verification.
- New `CODE_REVIEW.md` stub must use the same header and list every new plan item unchecked.
+
+`CODE_REVIEW.md` stub template (fill `{…}` placeholders; everything else is fixed and must not be changed by the implementing agent):
+
+```markdown
+<!-- task={task_name} plan={N} tag={TAG} -->
+
+# Code Review Reference - {TAG}
+
+## 개요
+
+task={task_name}, plan={N}, tag={TAG}
+
+## 이 파일을 읽는 리뷰 에이전트에게
+
+각 항목의 구현을 실제 소스 파일과 대조하고, `검증 결과` 섹션의 출력이 코드와 일치하는지 확인하세요.
+리뷰 완료 후 반드시 아래 순서로 아카이브하세요.
+
+1. `CODE_REVIEW.md` → `code_review_N.log` (N = 기존 code_review_*.log 수)
+2. `PLAN.md` → `plan_M.log` (M = 기존 plan_*.log 수)
+3. PASS인 경우 `complete.log` 작성 후 종료. WARN/FAIL인 경우 새 `PLAN.md` + `CODE_REVIEW.md` 스텁 작성.
+
+---
+
+## 구현 항목별 완료 여부
+
+| 항목 | 완료 여부 |
+|------|---------|
+| [{TAG}-1] {item description} | [ ] |
+| [{TAG}-2] {item description} | [ ] |
+
+## 계획 대비 변경 사항
+
+_구현 에이전트가 계획과 다르게 구현한 부분을 이유와 함께 기록한다._
+
+## 주요 설계 결정
+
+_구현 에이전트가 주요 설계 결정 사항을 기록한다._
+
+## 리뷰어를 위한 체크포인트
+
+{pre-filled from plan — one bullet per review focus area}
+
+## 검증 결과
+
+_구현 에이전트가 각 중간 검증 및 최종 검증 명령 실행 후 출력을 여기에 붙여 넣는다._
+
+### {TAG}-1 중간 검증
+```
+$ {verification command from plan}
+(output)
+```
+
+### 최종 검증
+```
+$ {final verification command from plan}
+(output)
+```
+```
+
+Sections and their ownership:
+
+| 섹션 | 소유자 | 설명 |
+|------|--------|------|
+| 헤더 주석, 개요, 리뷰 에이전트 지시 | 스텁 생성 시 고정 | 구현 에이전트가 수정하지 않음 |
+| 구현 항목별 완료 여부 (항목명) | 스텁 생성 시 고정 | `[ ]` → `[x]` 체크만 구현 에이전트가 수행 |
+| 계획 대비 변경 사항, 주요 설계 결정 | 구현 에이전트가 채움 | placeholder 텍스트를 실제 내용으로 교체 |
+| 리뷰어를 위한 체크포인트 | 스텁 생성 시 고정 | 계획에서 추출한 리뷰 포인트 |
+| 검증 결과 (섹션 제목 + 명령) | 스텁 생성 시 고정 | 실행 출력만 구현 에이전트가 채움 |
+| 코드리뷰 결과 | 리뷰 에이전트가 append | 스텁에 포함하지 않음 |

 Report Required/Suggested counts, archive names, and the new plan path.

@ -135,4 +213,5 @@ Report Required/Suggested counts, archive names, and the new plan path.
 - `code_review_N.log` exists with verdict appended.
 - `plan_M.log` exists.
 - No active `.md` files remain after PASS.
- WARN/FAIL created new active `PLAN.md` and `CODE_REVIEW.md` with matching headers.
+- PASS: `complete.log` written with loop history, implementation summary, and residual Nits.
+- WARN/FAIL: new active `PLAN.md` and `CODE_REVIEW.md` created with matching headers; no `complete.log`.
--- a/tasks/kotlin_impl/code_review_0.log
+++ b/tasks/kotlin_impl/code_review_0.log
@ -0,0 +1,233 @@
+<!-- task=kotlin_impl plan=0 tag=API -->
+
+# Code Review Reference - API
+
+## 개요
+
+task=kotlin_impl, plan=0, tag=API
+
+## 구현 항목별 완료 여부
+
+| 항목 | 완료 여부 |
+|------|---------|
+| [API-1] Kotlin 프로젝트 구조 및 proto 바인딩 설정 | [x] 구현 완료 / JVM 부재로 Gradle 검증 차단 |
+| [API-2] Communicator 구현 | [x] 구현 완료 / JVM 부재로 Gradle 검증 차단 |
+| [API-3] HeartbeatTimer 구현 | [x] 구현 완료 / JVM 부재로 Gradle 검증 차단 |
+| [API-4] BaseClient 구현 | [x] 구현 완료 / JVM 부재로 Gradle 검증 차단 |
+| [API-5] TcpClient / TcpServer 구현 | [x] 구현 완료 / JVM 부재로 Gradle 검증 차단 |
+| [API-6] WsClient / WsServer 구현 | [x] 구현 완료 / JVM 부재로 Gradle 검증 차단 |
+| [API-7] Heartbeat 통합 테스트 | [x] 작성 완료 / JVM 부재로 Gradle 검증 차단 |
+| [API-8] Go ↔ Kotlin 크로스테스트 | [x] 작성 완료 / JVM 부재로 Kotlin 실행 차단 |
+
+## 계획 대비 변경 사항
+
+- `go/crosstest/go_dart.go`와 `go/crosstest/go_kotlin.go`에 `//go:build ignore`를 추가했다. 두 파일 모두 단독 `go run ./crosstest/<file>.go` 오케스트레이터라서 같은 `package main` 안에 둘 경우 `go test ./...`에서 `main` 및 helper symbol이 충돌하기 때문이다. 명시 파일 `go run`은 유지된다.
+- `tools/check_proto_sync.sh`가 Kotlin proto copy도 검사하도록 확장했다. Java/Kotlin 생성용 `option java_*`만 canonical diff에서 제외한다.
+- `README.md`와 `PROTOCOL.md`의 Kotlin 상태는 `Available`이 아니라 `In progress`로 기록했다. 현재 컨테이너에 Java runtime이 없어 Kotlin 테스트와 크로스테스트를 실제 통과시키지 못했기 때문이다.
+- Heartbeat 통합 테스트는 `runTest` 가상 시간이 아니라 `runBlocking` 실제 시간 기반으로 작성했다. `BaseClient`가 `Dispatchers.IO` scope를 소유하는 현재 구조에서는 가상 스케줄러만으로 transport 통합 흐름이 진행되지 않는다.
+- `DialWss`는 API 표면을 추가했지만, 주어진 `SSLContext`에서 `X509TrustManager`를 안전하게 복원하는 경로는 아직 보수적으로 제한되어 있다. WSS 실검증은 후속 JVM 환경에서 보강 대상이다.
+
+## 주요 설계 결정
+
+- Kotlin proto는 schema package를 추가하지 않고 Java/Kotlin generation option만 둔다. `typeNameOf`는 `descriptorForType.fullName`을 사용하므로 현재 wire key는 Go/Dart와 같은 `TestData`, `HeartBeat`이다.
+- `Communicator`는 `Channel<QueuedPacket>(64)` 기반 단일 write loop로 stream write interleaving을 방지한다. pending request는 `responseNonce`로 제거하며, type mismatch는 waiting caller에 오류로 전달한다.
+- `addListener`와 `addRequestListener`는 `ReentrantReadWriteLock` write lock 안에서 상호 배타 조건을 검사한다.
+- `BaseClient.close()`는 `AtomicBoolean.compareAndSet(false, true)`로 멱등성을 보장하고, communicator shutdown, heartbeat stop, transport close, disconnect listener notify 순서로 처리한다.
+- TCP는 4-byte big-endian length prefix와 64 MiB max packet guard를 적용한다. WebSocket은 binary frame 하나에 `PacketBase` protobuf bytes를 싣는다.
+- Go crosstest runner는 Go 서버/Kotlin 클라이언트, Kotlin runner는 Kotlin 서버/Go 클라이언트 방향을 각각 담당한다.
+
+## 리뷰어를 위한 체크포인트
+
+- Communicator의 `addListener` / `addRequestListener` 상호 배타 로직이 race-free한가?
+- `close()` 멱등성: `AtomicBoolean.compareAndSet` 패턴이 모든 코드 경로에서 일관되게 적용됐는가?
+- writeLoop가 `writeQueue.close()` 후 정상 종료되는가? (pending done 채널에 오류 전달 여부 확인)
+- TCP readLoop에서 `length > MAX_PACKET_SIZE` 조건이 실제로 disconnect를 트리거하는가?
+- WsClient OkHttp `WebSocketListener.onFailure` → `onDisconnected` 경로가 누락되지 않았는가?
+- HeartbeatTimer가 `BaseClient.close()` 이후 callback을 발사하지 않는가? (scope 취소 순서 확인)
+- 크로스테스트 포트(29290, 29292, 29390, 29392)가 기존 테스트 포트와 충돌하지 않는가?
+- typeName이 `TestData` (단순 이름, no package prefix)로 Go / Dart 측과 일치하는가?
+
+## 검증 결과
+
+_구현 에이전트가 각 중간 검증 및 최종 검증 명령 실행 후 출력을 여기에 붙여 넣는다._
+
+### API-1 중간 검증
+```
+$ cd kotlin && ./gradlew compileKotlin
+
+ERROR: JAVA_HOME is not set and no 'java' command could be found in your PATH.
+
+Please set the JAVA_HOME variable in your environment to match the
+location of your Java installation.
+```
+
+### API-2 중간 검증
+```
+$ cd kotlin && ./gradlew test --tests "*.CommunicatorTest"
+
+ERROR: JAVA_HOME is not set and no 'java' command could be found in your PATH.
+
+Please set the JAVA_HOME variable in your environment to match the
+location of your Java installation.
+```
+
+### API-3 중간 검증
+```
+$ cd kotlin && ./gradlew test --tests "*.HeartbeatTimerTest"
+
+Not rerun separately: same Gradle/JVM blocker as API-2.
+```
+
+### API-4 중간 검증
+```
+$ cd kotlin && ./gradlew compileKotlin
+
+Not rerun separately: same Gradle/JVM blocker as API-1.
+```
+
+### API-5 중간 검증
+```
+$ cd kotlin && ./gradlew test --tests "*.TcpTest"
+
+Not rerun separately: same Gradle/JVM blocker as API-2.
+```
+
+### API-6 중간 검증
+```
+$ cd kotlin && ./gradlew test --tests "*.WsTest"
+
+Not rerun separately: same Gradle/JVM blocker as API-2.
+```
+
+### API-7 중간 검증
+```
+$ cd kotlin && ./gradlew test --tests "*.HeartbeatTest"
+
+Not rerun separately: same Gradle/JVM blocker as API-2.
+```
+
+### API-8 중간 검증
+```
+$ cd go && PATH=/config/go-sdk/go/bin:/config/go/bin:$PATH GOCACHE=/tmp/go-build GOMODCACHE=/tmp/go-mod go run ./crosstest/go_kotlin.go
+INFO typeName go=TestData
+
+ERROR: JAVA_HOME is not set and no 'java' command could be found in your PATH.
+
+Please set the JAVA_HOME variable in your environment to match the
+location of your Java installation.
+
+FAIL crosstest error=kotlin-client tcp/send-push failed waitErr=exit status 1 failed=[] missing=[1 2]
+exit status 1
+```
+
+### 최종 검증
+```
+$ cd go && PATH=/config/go-sdk/go/bin:/config/go/bin:$PATH GOCACHE=/tmp/go-build GOMODCACHE=/tmp/go-mod go test ./...
+?   	toki-labs.com/toki_socket/go	[no test files]
+?   	toki-labs.com/toki_socket/go/crosstest/dart_go_client	[no test files]
+?   	toki-labs.com/toki_socket/go/crosstest/kotlin_go_client	[no test files]
+?   	toki-labs.com/toki_socket/go/examples/tcp_echo	[no test files]
+?   	toki-labs.com/toki_socket/go/examples/ws_echo	[no test files]
+?   	toki-labs.com/toki_socket/go/packets	[no test files]
+ok  	toki-labs.com/toki_socket/go/test	(cached)
+
+$ ./tools/check_proto_sync.sh
+Proto schemas are in sync.
+
+$ cd kotlin && ./gradlew test
+
+ERROR: JAVA_HOME is not set and no 'java' command could be found in your PATH.
+
+Please set the JAVA_HOME variable in your environment to match the
+location of your Java installation.
+```
+
+---
+
+## 코드리뷰 결과
+
+### 종합 판정
+
+**WARN**
+
+---
+
+### 차원별 평가
+
+| 차원 | 판정 | 비고 |
+|------|------|------|
+| 정확성 (Correctness) | Pass | 프로토콜 wire format, nonce 단조 증가, close-once, addListener/addRequestListener 상호 배타, pending request 취소 모두 올바름 |
+| 완성도 (Completeness) | Pass | 8개 항목 전부 구현됨. proto sync 검증, Go 테스트 회귀 없음 확인 |
+| 테스트 커버리지 (Test coverage) | Warn | HeartbeatTest의 reset 테스트가 실제 메시지 수신 경로를 커버하지 않음 |
+| API 계약 (API contract) | Warn | `crosstest/` 소스가 main sourceset에 포함되어 라이브러리 JAR에 crosstest 코드가 실려감 |
+| 코드 품질 (Code quality) | Warn | `WsServer.stop()`의 `InterruptedException` 미처리, `kotlin_go.kt` 내 `runBlocking` in listener |
+| 계획 대비 변경 (Plan deviation) | Pass | 모든 변경이 CODE_REVIEW.md에 기록되고 이유가 명확함 |
+| 검증 신뢰도 (Verification trust) | Pass | JVM 환경 부재로 Kotlin 검증 불가, 가능한 Go 검증은 모두 실행됨. 제약이 명확히 기록됨 |
+
+---
+
+### 발견된 문제
+
+**Suggested — `WsServer.stop()`: `super.stop(1000)` `InterruptedException` 미처리**
+`kotlin/src/main/kotlin/com/tokilabs/toki_socket/WsServer.kt:36-41`
+
+`WebSocketServer.stop(int)` 는 Java 메서드로 `InterruptedException` 을 선언한다. Kotlin은 checked exception을 컴파일 타임에 강제하지 않지만, `runBlocking` 컨텍스트에서 `InterruptedException` 이 던져지면 현재 coroutine이 취소 신호로 처리해 `stop()` 이후 로직이 실행되지 않는다.
+
+```kotlin
+// 현재
+super.stop(1000)
+
+// 수정
+runCatching { super.stop(1000) }
+```
+
+---
+
+**Suggested — `crosstest/` 코드가 main sourceset에 포함됨**
+`kotlin/build.gradle.kts:14`
+
+```kotlin
+named("main") {
+    kotlin.srcDir("crosstest")
+}
+```
+
+`kotlin_go.kt` 와 `go_kotlin_client/` 의 `Main.kt` 가 라이브러리 JAR에 함께 포함된다. crosstest 코드는 별도 sourceset(`crosstestMain`) 이나 `application` 전용 소스 경로로 분리해야 한다.
+
+---
+
+**Suggested — `kotlin_go.kt` listener callback 내 `runBlocking` 사용**
+`kotlin/crosstest/kotlin_go.kt:56-63`, `104-111`
+
+```kotlin
+addListenerTyped<TestData>(client.communicator) { data ->
+    ...
+    if (valid) {
+        runBlocking { client.send(...) }  // ← Dispatchers.IO 스레드 블로킹
+    }
+}
+```
+
+`onReceivedData` 는 `TcpClient.readLoop` 의 `Dispatchers.IO` coroutine 내에서 호출된다. listener callback에서 `runBlocking` 을 호출하면 IO 스레드를 점유한다. `scope.launch { client.send(...) }` 또는 listener를 `suspend` 람다로 받는 패턴으로 교체해야 한다.
+
+현재 `addListenerTyped` 의 시그니처가 `fn: (T) -> Unit` 이므로 즉시 수정하려면 코드 내부에서 `scope.launch { }` 로 감싸거나, crosstest 코드 한정으로 별도 scope를 사용해야 한다.
+
+---
+
+**Suggested — `HeartbeatTest.testHeartbeatResetOnReceive()`: 수신 경로 미검증**
+`kotlin/src/test/kotlin/com/tokilabs/toki_socket/HeartbeatTest.kt:69-81`
+
+테스트 이름은 "receive 시 타이머 리셋"이지만 실제로는 `sendHeartBeat()` 를 직접 두 번 호출한다. 실제 경로인 `onReceivedData()` → `sendHeartBeat()` 를 통한 타이머 리셋이 검증되지 않는다. 테스트에서 `TcpClient` 또는 `HeartbeatClient` 의 `communicator.onReceivedData(...)` 를 호출하고 heartbeat가 지연되는지 확인해야 한다.
+
+---
+
+**Nit — `Communicator.parse()` 가 public으로 노출됨**
+`kotlin/src/main/kotlin/com/tokilabs/toki_socket/Communicator.kt:266`
+
+Go 구현에서는 `parse` 가 unexported이다. Kotlin에서도 `internal` 로 제한하는 것이 적절하다. 현재 inline helper (`addRequestListenerTyped`) 는 `queuePacket`, `nextNonce` 만 필요하고 `parse` 를 직접 호출하지 않는다.
+
+---
+
+### 다음 단계
+
+WARN: Suggested 항목을 수정하는 후속 PLAN.md 가 작성된다. 수정 완료 후 재리뷰.
--- a/tasks/kotlin_impl/code_review_1.log
+++ b/tasks/kotlin_impl/code_review_1.log
@ -0,0 +1,254 @@
+<!-- task=kotlin_impl plan=1 tag=REVIEW_API -->
+
+# Code Review Reference - REVIEW_API
+
+## 개요
+
+task=kotlin_impl, plan=1, tag=REVIEW_API
+
+## 구현 항목별 완료 여부
+
+| 항목 | 완료 여부 |
+|------|---------|
+| [REVIEW_API-1] `WsServer.stop()` `InterruptedException` 미처리 수정 | [x] |
+| [REVIEW_API-2] `crosstest/` 를 main sourceset에서 분리 | [x] |
+| [REVIEW_API-3] `kotlin_go.kt` listener 내 `runBlocking` 제거 | [x] |
+| [REVIEW_API-4] `HeartbeatTest.testHeartbeatTimerResetOnReceivedData` 테스트 추가 | [x] |
+| [REVIEW_API-5] `Communicator.parse()` visibility `internal` 로 제한 | [x] |
+
+## 계획 대비 변경 사항
+
+- REVIEW_API-3의 listener send는 계획의 `client.scope.launch` 대신 `runTcpSendPush`/`runWsSendPush`를 `coroutineScope`로 감싸고 해당 scope의 `launch`를 사용했다. `crosstest`를 main sourceset에서 분리하면 main의 `internal` 멤버 접근이 별도 compilation에서 막힐 수 있어, crosstest runner가 main 내부 scope에 의존하지 않도록 했다.
+- REVIEW_API-3 구현 중 `WsClient.forServer`도 `internal`이면 분리된 crosstest sourceset에서 `kotlin_go.kt`가 접근할 수 없다. 또한 public `WsServer` 생성자에서 기본 server-side `WsClient`를 만들 방법이 필요하므로 `WsClient.forServer`를 public companion factory로 조정했다.
+- REVIEW_API-3 검증 중 분리된 crosstest sourceset에서 `parserMap()`의 `TestData.parseFrom(it)` overload 추론이 모호해져 `parserMap(): ParserMap` 반환 타입을 명시했다.
+- REVIEW_API-4의 수신 경로 테스트는 `TestData` listener를 등록하고 `received` 플래그를 확인해 `onReceivedData()`가 실제 listener dispatch까지 통과했는지도 검증한다.
+- 최종 검증 중 `TcpTest` class 실행이 timeout 된 뒤 메서드 단위로 분리해 확인했다. `testTcpClientCloseIdempotent`의 blocking `ServerSocket.accept()`를 `Dispatchers.IO`에서 실행하도록 바꿔 테스트 스레드 점유 위험을 낮췄고, 이후 `TcpTest`, `WsTest`, 전체 `./gradlew test`가 통과했다.
+
+## 주요 설계 결정
+
+- `crosstest` sourceset은 main 출력과 runtime classpath를 compile/runtime classpath로 갖도록 구성했다.
+- `run` task는 `crosstest` runtime classpath에서 기본 crosstest main class를 실행하도록 재구성했다.
+- `BaseClient.scope`는 계획대로 `internal`로 제한했지만, crosstest runner는 이 scope를 직접 참조하지 않는다.
+- Gradle 검증은 `JAVA_HOME=/config/opt/jdk/jdk-17.0.10+7`, `GRADLE_USER_HOME=/tmp/gradle` 환경으로 실행했다.
+
+## 리뷰어를 위한 체크포인트
+
+- `crosstest` sourceset 분리 후 `./gradlew run` 이 여전히 `MainKt` 를 실행하는가?
+- `BaseClient.scope` 를 `internal` 로 노출 시 외부 모듈에서 scope를 직접 조작하는 위험이 없는가?
+- `testHeartbeatTimerResetOnReceivedData` 가 `onReceivedData` 경로를 실제로 통과하는가?
+- JAR 에 crosstest 클래스가 포함되지 않는가?
+
+## 검증 결과
+
+_구현 에이전트가 각 중간 검증 및 최종 검증 명령 실행 후 출력을 여기에 붙여 넣는다._
+
+### REVIEW_API-1 중간 검증
+```
+$ ./gradlew compileKotlin
+> Task :checkKotlinGradlePluginConfigurationErrors SKIPPED
+> Task :extractIncludeProto UP-TO-DATE
+> Task :extractProto UP-TO-DATE
+> Task :generateProto UP-TO-DATE
+> Task :compileKotlin UP-TO-DATE
+
+BUILD SUCCESSFUL in 13s
+4 actionable tasks: 4 up-to-date
+```
+
+### REVIEW_API-2 중간 검증
+```
+$ ./gradlew compileKotlin compileCrosstestKotlin
+> Task :checkKotlinGradlePluginConfigurationErrors SKIPPED
+> Task :extractIncludeProto UP-TO-DATE
+> Task :extractProto UP-TO-DATE
+> Task :generateProto UP-TO-DATE
+> Task :compileKotlin UP-TO-DATE
+> Task :compileJava UP-TO-DATE
+> Task :processResources UP-TO-DATE
+> Task :classes UP-TO-DATE
+> Task :extractCrosstestProto UP-TO-DATE
+> Task :extractIncludeCrosstestProto UP-TO-DATE
+> Task :generateCrosstestProto NO-SOURCE
+> Task :compileCrosstestKotlin
+
+BUILD SUCCESSFUL in 11s
+9 actionable tasks: 1 executed, 8 up-to-date
+
+$ ./gradlew jar
+> Task :checkKotlinGradlePluginConfigurationErrors SKIPPED
+> Task :extractIncludeProto UP-TO-DATE
+> Task :extractProto UP-TO-DATE
+> Task :generateProto UP-TO-DATE
+> Task :compileKotlin UP-TO-DATE
+> Task :compileJava UP-TO-DATE
+> Task :processResources UP-TO-DATE
+> Task :classes UP-TO-DATE
+> Task :jar
+
+BUILD SUCCESSFUL in 3s
+7 actionable tasks: 1 executed, 6 up-to-date
+
+$ jar tf build/libs/toki-socket-kotlin-0.1.0.jar | grep crosstest
+(no output)
+```
+
+### REVIEW_API-3 중간 검증
+```
+$ ./gradlew compileCrosstestKotlin
+> Task :checkKotlinGradlePluginConfigurationErrors SKIPPED
+> Task :extractIncludeProto UP-TO-DATE
+> Task :extractProto UP-TO-DATE
+> Task :generateProto UP-TO-DATE
+> Task :compileKotlin UP-TO-DATE
+> Task :compileJava UP-TO-DATE
+> Task :processResources UP-TO-DATE
+> Task :classes UP-TO-DATE
+> Task :extractCrosstestProto UP-TO-DATE
+> Task :extractIncludeCrosstestProto UP-TO-DATE
+> Task :generateCrosstestProto NO-SOURCE
+> Task :compileCrosstestKotlin UP-TO-DATE
+
+BUILD SUCCESSFUL in 3s
+9 actionable tasks: 9 up-to-date
+```
+
+### REVIEW_API-4 중간 검증
+```
+$ ./gradlew test --tests "*.HeartbeatTest"
+> Task :checkKotlinGradlePluginConfigurationErrors SKIPPED
+> Task :extractIncludeProto UP-TO-DATE
+> Task :extractProto UP-TO-DATE
+> Task :generateProto UP-TO-DATE
+> Task :compileKotlin UP-TO-DATE
+> Task :compileJava UP-TO-DATE
+> Task :processResources UP-TO-DATE
+> Task :classes UP-TO-DATE
+> Task :extractIncludeTestProto UP-TO-DATE
+> Task :extractTestProto UP-TO-DATE
+> Task :generateTestProto NO-SOURCE
+> Task :compileTestKotlin UP-TO-DATE
+> Task :compileTestJava NO-SOURCE
+> Task :processTestResources NO-SOURCE
+> Task :testClasses UP-TO-DATE
+> Task :test
+
+BUILD SUCCESSFUL in 15s
+10 actionable tasks: 1 executed, 9 up-to-date
+```
+
+### REVIEW_API-5 중간 검증
+```
+$ ./gradlew compileKotlin compileTestKotlin
+> Task :checkKotlinGradlePluginConfigurationErrors SKIPPED
+> Task :extractIncludeProto UP-TO-DATE
+> Task :extractProto UP-TO-DATE
+> Task :generateProto UP-TO-DATE
+> Task :compileKotlin UP-TO-DATE
+> Task :compileJava UP-TO-DATE
+> Task :processResources UP-TO-DATE
+> Task :classes UP-TO-DATE
+> Task :extractIncludeTestProto UP-TO-DATE
+> Task :extractTestProto UP-TO-DATE
+> Task :generateTestProto NO-SOURCE
+> Task :compileTestKotlin
+
+BUILD SUCCESSFUL in 8s
+9 actionable tasks: 1 executed, 8 up-to-date
+```
+
+### 최종 검증
+```
+$ ./gradlew test
+> Task :checkKotlinGradlePluginConfigurationErrors SKIPPED
+> Task :extractIncludeProto UP-TO-DATE
+> Task :extractProto UP-TO-DATE
+> Task :generateProto UP-TO-DATE
+> Task :compileKotlin UP-TO-DATE
+> Task :compileJava UP-TO-DATE
+> Task :processResources UP-TO-DATE
+> Task :classes UP-TO-DATE
+> Task :extractIncludeTestProto UP-TO-DATE
+> Task :extractTestProto UP-TO-DATE
+> Task :generateTestProto NO-SOURCE
+> Task :compileTestKotlin UP-TO-DATE
+> Task :compileTestJava NO-SOURCE
+> Task :processTestResources NO-SOURCE
+> Task :testClasses UP-TO-DATE
+> Task :test
+
+BUILD SUCCESSFUL in 16s
+10 actionable tasks: 1 executed, 9 up-to-date
+
+$ ./gradlew jar
+> Task :checkKotlinGradlePluginConfigurationErrors SKIPPED
+> Task :extractIncludeProto UP-TO-DATE
+> Task :extractProto UP-TO-DATE
+> Task :generateProto UP-TO-DATE
+> Task :compileKotlin UP-TO-DATE
+> Task :compileJava UP-TO-DATE
+> Task :processResources UP-TO-DATE
+> Task :classes UP-TO-DATE
+> Task :jar
+
+BUILD SUCCESSFUL in 3s
+7 actionable tasks: 1 executed, 6 up-to-date
+
+$ jar tf build/libs/toki-socket-kotlin-0.1.0.jar | grep crosstest
+(no output)
+
+$ /usr/bin/bash -lc 'PATH=/config/go-sdk/go/bin:/config/go/bin:$PATH GOCACHE=/tmp/go-build GOMODCACHE=/tmp/go-mod go test ./...'
+?   	toki-labs.com/toki_socket/go	[no test files]
+?   	toki-labs.com/toki_socket/go/crosstest/dart_go_client	[no test files]
+?   	toki-labs.com/toki_socket/go/crosstest/kotlin_go_client	[no test files]
+?   	toki-labs.com/toki_socket/go/examples/tcp_echo	[no test files]
+?   	toki-labs.com/toki_socket/go/examples/ws_echo	[no test files]
+?   	toki-labs.com/toki_socket/go/packets	[no test files]
+ok  	toki-labs.com/toki_socket/go/test	(cached)
+
+$ bash tools/check_proto_sync.sh
+Proto schemas are in sync.
+```
+
+---
+
+## 코드리뷰 결과
+
+### 종합 판정
+
+**PASS**
+
+---
+
+### 차원별 평가
+
+| 차원 | 판정 | 비고 |
+|------|------|------|
+| 정확성 (Correctness) | Pass | REVIEW_API-1~5 모두 의도대로 구현됨. 멱등성, race 보호, crosstest 분리 정상 |
+| 완성도 (Completeness) | Pass | 5개 항목 전부 구현. `./gradlew test`, `jar`, Go 테스트, proto sync 통과 |
+| 테스트 커버리지 (Test coverage) | Pass | `testHeartbeatTimerResetOnReceivedData` 추가. listener dispatch 경로 검증 포함 |
+| API 계약 (API contract) | Pass | crosstest가 JAR에서 제외됨 확인. `parse()` internal 제한 |
+| 코드 품질 (Code quality) | Pass | `runBlocking` in listener 제거, `InterruptedException` 처리 완료 |
+| 계획 대비 변경 (Plan deviation) | Pass | 모든 변경이 CODE_REVIEW.md에 이유와 함께 기록됨 |
+| 검증 신뢰도 (Verification trust) | Pass | JVM 환경에서 전 항목 실제 실행 확인 |
+
+---
+
+### 발견된 문제
+
+**Nit — `testHeartbeatTimerResetOnReceivedData` 테스트 이름과 검증 범위 불일치**
+`kotlin/src/test/kotlin/com/tokilabs/toki_socket/HeartbeatTest.kt:84-106`
+
+테스트 이름은 "수신 데이터에 의한 타이머 리셋"이지만, 타이머를 실제로 리셋하는 것은 `onReceivedData` 이후 명시적으로 호출하는 `sendHeartBeat()`이다. `onReceivedData` 자체가 타이머를 리셋하는 경로(`TcpClient.readLoop`, `WsClient.receiveBytes`에서 `sendHeartBeat()` 호출)는 `HeartbeatClient`에서 재현되지 않는다. `received` 플래그 확인으로 listener dispatch는 검증되나, 테스트 이름이 과장된다. 블로킹 이슈는 아님.
+
+---
+
+**Info — `build.gradle.kts` `application.mainClass` 중복 설정**
+`kotlin/build.gradle.kts:46-60`
+
+`application { mainClass }` 와 `tasks.named<JavaExec>("run") { mainClass }` 에 동일한 값이 중복 설정되어 있다. `tasks.named("run")`이 오버라이드하므로 `application { }` 블록의 설정은 실질적으로 무효이다. 기능상 문제는 없으나 `application { mainClass }` 제거 또는 주석 추가가 명확하다.
+
+---
+
+### 다음 단계
+
+PASS: 후속 PLAN.md 없음. kotlin_impl 완료.
--- a/tasks/kotlin_impl/complete.log
+++ b/tasks/kotlin_impl/complete.log
@ -0,0 +1,31 @@
+# Task Complete — kotlin_impl
+
+## 완료 일시
+
+2026-04-12
+
+## 요약
+
+Kotlin 구현 후속 수정 (REVIEW_API) — plan=1, tag=REVIEW_API
+
+plan-code-review 루프 2회 완료 후 PASS 판정으로 종료.
+
+## 루프 이력
+
+| 회차 | 계획 | 리뷰 | 판정 |
+|------|------|------|------|
+| 0 | plan_0.log | code_review_0.log | WARN |
+| 1 | plan_1.log | code_review_1.log | PASS |
+
+## 최종 리뷰 요약 (plan=1)
+
+- REVIEW_API-1: `WsServer.stop()` `InterruptedException` 미처리 → `runCatching` 으로 처리
+- REVIEW_API-2: `crosstest/` 를 main sourceset에서 분리 → JAR에 crosstest 미포함 확인
+- REVIEW_API-3: `kotlin_go.kt` listener 내 `runBlocking` 제거 → `coroutineScope` + `launch` 대체
+- REVIEW_API-4: `testHeartbeatTimerResetOnReceivedData` 테스트 추가
+- REVIEW_API-5: `Communicator.parse()` visibility `internal` 로 제한
+
+## 잔여 Nit
+
+- `testHeartbeatTimerResetOnReceivedData` 테스트 이름이 검증 범위를 과장 (블로킹 아님)
+- `build.gradle.kts` `application.mainClass` 중복 설정 (기능 영향 없음)
--- a/tasks/kotlin_impl/plan_0.log
+++ b/tasks/kotlin_impl/plan_0.log
@ -0,0 +1,807 @@
+<!-- task=kotlin_impl plan=0 tag=API -->
+
+# Kotlin 구현체 신규 추가
+
+## 이 파일을 읽는 구현 에이전트에게
+
+각 항목의 체크리스트를 하나씩 완료 처리하고, 중간 검증 명령을 실제로 실행한 뒤 출력을 `CODE_REVIEW.md`의 `검증 결과` 섹션에 붙여 넣으세요.
+계획과 다르게 구현한 부분이 있으면 `계획 대비 변경 사항`에 이유와 함께 기록하세요.
+`CODE_REVIEW.md`의 모든 섹션을 실제 구현 내용으로 채운 뒤 코드 리뷰를 요청하세요.
+
+---
+
+## 배경
+
+`PROTOCOL.md`에 기술된 Toki Socket 프로토콜의 Kotlin 구현체가 없다. Go/Dart 레퍼런스 구현체를 기준으로 동일한 wire format(TCP 4-byte big-endian framing, WebSocket binary frame), typeName 라우팅, request-response nonce 상관관계, heartbeat 자동 처리를 Kotlin coroutine 관용 패턴으로 구현한다. 구현 완료 기준은 같은 언어 단위 테스트 통과와 Go ↔ Kotlin 양방향 크로스테스트 통과이다.
+
+---
+
+## 의존 관계 및 구현 순서
+
+API-1 → API-2 → API-3 → API-4 → API-5 → API-6 → API-7 → API-8
+
+---
+
+### [API-1] Kotlin 프로젝트 구조 및 protobuf 바인딩 설정
+
+#### 문제
+
+`kotlin/` 디렉터리가 없고 프로젝트 파일, proto 바인딩이 없다.
+
+#### 해결 방법
+
+Gradle 멀티플랫폼이 아닌 순수 JVM 라이브러리 프로젝트로 설정한다. 빌드 도구는 Gradle Kotlin DSL(`build.gradle.kts`)을 사용한다.
+
+**디렉터리 구조:**
+
+```
+kotlin/
+  build.gradle.kts
+  settings.gradle.kts
+  gradlew  (gradle wrapper)
+  gradlew.bat
+  gradle/wrapper/
+  src/
+    main/
+      kotlin/com/tokilabs/toki_socket/
+      proto/                          ← canonical proto 복사본
+    test/
+      kotlin/com/tokilabs/toki_socket/
+  crosstest/
+    go_kotlin_client/                 ← Kotlin subprocess (Go 서버 ↔ Kotlin 클라이언트)
+    kotlin_go.kt                      ← Kotlin 서버 오케스트레이터 (Kotlin 서버 ↔ Go 클라이언트)
+```
+
+**`build.gradle.kts` 핵심 의존성:**
+
+```kotlin
+plugins {
+    kotlin("jvm") version "2.0.0"
+    id("com.google.protobuf") version "0.9.4"
+}
+
+dependencies {
+    implementation("org.jetbrains.kotlinx:kotlinx-coroutines-core:1.8.1")
+    implementation("com.google.protobuf:protobuf-kotlin:4.27.0")
+    implementation("com.squareup.okhttp3:okhttp:4.12.0")           // WS client
+    implementation("org.java-websocket:Java-WebSocket:1.5.6")       // WS server
+    testImplementation("org.jetbrains.kotlinx:kotlinx-coroutines-test:1.8.1")
+    testImplementation(kotlin("test"))
+}
+
+protobuf {
+    protoc { artifact = "com.google.protobuf:protoc:4.27.0" }
+    generateProtoTasks {
+        all().forEach { task ->
+            task.builtins {
+                id("kotlin")
+            }
+        }
+    }
+}
+```
+
+**proto 동기화:**
+`dart/lib/src/packets/message_common.proto`에서 `kotlin/src/main/proto/message_common.proto`로 복사. Go 처럼 언어별 option(`option java_package`, `option java_outer_classname`)을 추가할 수 있으나 **message schema는 canonical proto와 동일하게 유지**. `tools/check_proto_sync.sh`가 message 필드 diff를 검출한다.
+
+#### 수정 파일 및 체크리스트
+
+- [ ] `kotlin/settings.gradle.kts` 생성
+- [ ] `kotlin/build.gradle.kts` 생성 (위 의존성 포함)
+- [ ] Gradle wrapper 생성 (`gradle wrapper` 실행 또는 수동 배치)
+- [ ] `kotlin/src/main/proto/message_common.proto` 생성 (canonical proto 복사 + java options 추가)
+- [ ] `./gradlew generateProto` 실행하여 바인딩 생성 확인
+
+#### 테스트 작성
+
+SKIP — 이 항목은 빌드 인프라 설정이며 동작 검증은 이후 항목의 테스트로 커버된다.
+
+#### 중간 검증
+
+```bash
+cd kotlin
+./gradlew compileKotlin
+# 예상: BUILD SUCCESSFUL (proto 바인딩 포함 컴파일)
+```
+
+---
+
+### [API-2] Communicator 구현
+
+#### 문제
+
+Kotlin에 `Communicator`, `Transport`, `ParserMap` 타입이 없다.
+
+#### 해결 방법
+
+Go `communicator.go` 구조를 Kotlin coroutine 관용 패턴으로 이식한다.
+
+**파일:** `kotlin/src/main/kotlin/com/tokilabs/toki_socket/Communicator.kt`
+
+**핵심 매핑:**
+
+| Go | Kotlin |
+|----|--------|
+| `Transport` interface | `interface Transport` |
+| `ParserMap` | `typealias ParserMap = Map<String, (ByteArray) -> MessageLite>` |
+| `atomic.Int32` (nonce) | `AtomicInteger` |
+| `atomic.Bool` (isAlive) | `AtomicBoolean` |
+| `sync.RWMutex` | `ReentrantReadWriteLock` |
+| `channel queuedPacket (64)` | `Channel<QueuedPacket>(capacity = 64)` |
+| `closed chan struct{}` | `Job` (coroutine cancellation) |
+| `sync.Once` (closeOnce) | 없음 — `shutdown()`은 `closeOnce` 없이 AtomicBoolean + coroutine cancel |
+| goroutine writeLoop | `scope.launch { writeLoop() }` |
+
+**typeName 추출:**
+
+```kotlin
+fun typeNameOf(m: MessageLite): String =
+    (m as com.google.protobuf.Message).descriptorForType.fullName
+```
+
+proto에 `package` 선언이 없으므로 `fullName` = `"TestData"`, `"HeartBeat"` 등 단순 이름. PROTOCOL.md Kotlin 행과 일치.
+
+**`addListener` / `addRequestListener` 상호 배타:**
+
+```kotlin
+fun addRequestListener(typeName: String, fn: (MessageLite, Int) -> Unit) {
+    val lock = rwLock.writeLock()
+    lock.lock()
+    try {
+        check(handlers[typeName].isNullOrEmpty()) {
+            "type $typeName is already registered with addListener"
+        }
+        check(!reqHandlers.containsKey(typeName)) {
+            "type $typeName is already registered with addRequestListener"
+        }
+        reqHandlers[typeName] = fn
+    } finally { lock.unlock() }
+}
+```
+
+위반 시 `IllegalStateException`(Go의 `panic` 대응).
+
+**`writeLoop`:**
+
+```kotlin
+private suspend fun writeLoop() {
+    for (item in writeQueue) {
+        val err = runCatching { transport.writePacket(item.base) }
+        item.done.complete(err.exceptionOrNull())
+        if (err.isFailure) {
+            writeErrorHandler?.invoke(err.exceptionOrNull()!!)
+        }
+    }
+}
+```
+
+**`sendRequest`:**
+
+```kotlin
+suspend fun sendRequest(
+    req: MessageLite,
+    resTypeName: String,
+    timeoutMs: Long = 30_000L
+): MessageLite {
+    ...
+    withTimeout(timeoutMs) {
+        select {
+            pending.ch.onReceive { it }
+            pending.errCh.onReceive { throw it }
+        }
+    }
+}
+```
+
+#### 수정 파일 및 체크리스트
+
+- [ ] `Communicator.kt` 생성
+  - [ ] `interface Transport { suspend fun writePacket(base: PacketBase); fun close() }`
+  - [ ] `typealias ParserMap = Map<String, (ByteArray) -> MessageLite>`
+  - [ ] `class Communicator(transport, parserMap, scope)` 생성자
+  - [ ] `initialize()`: HeartBeat 파서 자동 등록, writeLoop launch
+  - [ ] `isAlive(): Boolean`
+  - [ ] `nextNonce()`: AtomicInteger.incrementAndGet()
+  - [ ] `shutdown()`: isAlive=false, writeQueue.close(), scope 내부 채널 정리
+  - [ ] `close()`: shutdown() + transport.close()
+  - [ ] `queuePacket(base)`: writeQueue에 enqueue, done 대기
+  - [ ] `send(m)`: marshal → queuePacket
+  - [ ] `sendRequest(req, resTypeName, timeout)`: nonce 등록 → queuePacket → withTimeout select
+  - [ ] `addListener(typeName, fn)`: 상호 배타 체크
+  - [ ] `removeListeners(typeName)`
+  - [ ] `addRequestListener(typeName, fn)`: 상호 배타 체크
+  - [ ] `onReceivedData(typeName, data, nonce, responseNonce)`
+  - [ ] `handleResponse(typeName, data, responseNonce)`
+  - [ ] `parse(typeName, data)`
+  - [ ] `removePending(nonce)`
+- [ ] 타입 헬퍼 함수 (Go의 제네릭 헬퍼 대응):
+  - [ ] `inline fun <reified T : Message> addListenerTyped(communicator, fn)`
+  - [ ] `inline fun <reified Req : Message, reified Res : Message> addRequestListenerTyped(communicator, fn)`
+  - [ ] `inline fun <reified Req : Message, reified Res : Message> sendRequestTyped(communicator, req, timeoutMs)`
+
+#### 테스트 작성
+
+**파일:** `kotlin/src/test/kotlin/com/tokilabs/toki_socket/CommunicatorTest.kt`
+
+| 테스트명 | 검증 목표 |
+|---------|---------|
+| `testSendRequestTimeout` | timeout 경과 시 exception 발생 |
+| `testSendRequestTypeMismatch` | 응답 typeName 불일치 시 exception 발생 |
+| `testListenerAndRequestListenerConflict` | 동일 typeName 이중 등록 시 IllegalStateException |
+| `testSendFireAndForget` | send 후 fakeTransport에 패킷 1개 기록됨 |
+
+#### 중간 검증
+
+```bash
+cd kotlin
+./gradlew test --tests "*.CommunicatorTest"
+# 예상: 4개 테스트 PASS
+```
+
+---
+
+### [API-3] HeartbeatTimer 구현
+
+#### 문제
+
+주기적 heartbeat 발송을 위한 취소 가능한 타이머가 없다.
+
+#### 해결 방법
+
+Go의 `HeartbeatTimer`를 coroutine `delay` 기반으로 이식한다.
+
+**파일:** `kotlin/src/main/kotlin/com/tokilabs/toki_socket/HeartbeatTimer.kt`
+
+```kotlin
+class HeartbeatTimer(
+    private val scope: CoroutineScope,
+    private val delayMs: Long,
+    private val callback: suspend () -> Unit
+) {
+    private var job: Job? = null
+
+    fun reset(delayMs: Long = this.delayMs) {
+        job?.cancel()
+        job = scope.launch {
+            delay(delayMs)
+            callback()
+        }
+    }
+
+    fun stop() {
+        job?.cancel()
+        job = null
+    }
+}
+```
+
+`scope`는 `BaseClient`에서 생성된 `CoroutineScope(SupervisorJob() + Dispatchers.IO)`를 전달한다.
+
+#### 수정 파일 및 체크리스트
+
+- [ ] `HeartbeatTimer.kt` 생성
+  - [ ] `reset(delayMs)`: 기존 job cancel 후 새 delay job launch
+  - [ ] `stop()`: job cancel
+
+#### 테스트 작성
+
+**파일:** `kotlin/src/test/kotlin/com/tokilabs/toki_socket/HeartbeatTimerTest.kt`
+
+| 테스트명 | 검증 목표 |
+|---------|---------|
+| `testCallbackFires` | delay 후 callback 호출됨 |
+| `testStopPreventsCallback` | stop() 후 callback 미호출 |
+| `testResetRestartsTimer` | reset() 후 이전 callback 미호출, 새 delay 후 호출 |
+
+#### 중간 검증
+
+```bash
+cd kotlin
+./gradlew test --tests "*.HeartbeatTimerTest"
+# 예상: 3개 테스트 PASS
+```
+
+---
+
+### [API-4] BaseClient 구현
+
+#### 문제
+
+heartbeat 로직, disconnect 리스너, connCloseOnce(close-once) 공통 구조가 없다.
+
+#### 해결 방법
+
+Go의 `baseClient[Self]`를 `abstract class BaseClient<Self : BaseClient<Self>>`로 이식한다.
+
+**파일:** `kotlin/src/main/kotlin/com/tokilabs/toki_socket/BaseClient.kt`
+
+**핵심 매핑:**
+
+| Go | Kotlin |
+|----|--------|
+| `self Self` | 생성자 파라미터로 `self: Self` 수신 |
+| `connCloseOnce sync.Once` | `AtomicBoolean` + `compareAndSet(false, true)` |
+| `hbMu sync.Mutex` | `Mutex` (kotlinx.coroutines) |
+| `disconnectListeners` | `CopyOnWriteArrayList<(Self) -> Unit>` |
+| `doClose func() error` | 생성자 람다 `doClose: suspend () -> Unit` |
+
+```kotlin
+abstract class BaseClient<Self : BaseClient<Self>>(
+    private val self: Self,
+    intervalSec: Int,
+    waitSec: Int,
+    private val doClose: suspend () -> Unit
+) {
+    protected val scope = CoroutineScope(SupervisorJob() + Dispatchers.IO)
+    abstract val communicator: Communicator
+
+    private val heartbeatIntervalMs = intervalSec * 1000L
+    private val heartbeatWaitMs = waitSec * 1000L
+    private val closedOnce = AtomicBoolean(false)
+    private val hbMutex = Mutex()
+    private var hbTimer: HeartbeatTimer? = null
+    private var waitingHBResponse = false
+    private val disconnectListeners = CopyOnWriteArrayList<(Self) -> Unit>()
+
+    fun addDisconnectListener(handler: (Self) -> Unit) { disconnectListeners.add(handler) }
+    fun removeDisconnectListeners() { disconnectListeners.clear() }
+
+    suspend fun close() {
+        if (!closedOnce.compareAndSet(false, true)) return
+        communicator.shutdown()
+        stopHeartbeat()
+        doClose()
+        notifyDisconnected()
+        scope.cancel()
+    }
+
+    // sendHeartBeat, onHeartBeat, stopHeartbeat, onDisconnected, notifyDisconnected
+    // Go 로직과 동일하게 구현
+}
+```
+
+`close()`는 `connCloseOnce.compareAndSet(false, true)` 패턴으로 멱등성 보장. Go의 `sync.Once`와 동일 의미.
+
+#### 수정 파일 및 체크리스트
+
+- [ ] `BaseClient.kt` 생성
+  - [ ] `scope`: `CoroutineScope(SupervisorJob() + Dispatchers.IO)`
+  - [ ] `close()`: compareAndSet + communicator.shutdown() + stopHeartbeat() + doClose() + notifyDisconnected() + scope.cancel()
+  - [ ] `sendHeartBeat()`: hbMutex 잠금, 이전 타이머 정지, 새 interval 타이머 → HeartBeat 전송 → waitingHBResponse=true → wait 타이머 → onDisconnected
+  - [ ] `onHeartBeat()`: waitingHBResponse 분기 처리 (Go 로직 그대로)
+  - [ ] `stopHeartbeat()`: hbTimer?.stop()
+  - [ ] `onDisconnected()`: close() 호출
+  - [ ] `notifyDisconnected()`: listener 복사 후 순회 호출
+
+#### 테스트 작성
+
+SKIP — heartbeat 통합 동작은 API-7의 HeartbeatTest에서 TcpClient를 통해 검증한다. BaseClient 자체는 추상 클래스여서 단독 단위 테스트가 어렵다.
+
+#### 중간 검증
+
+```bash
+cd kotlin
+./gradlew compileKotlin
+# 예상: BUILD SUCCESSFUL (API-5 구현 전이므로 컴파일만 확인)
+```
+
+---
+
+### [API-5] TcpClient / TcpServer 구현
+
+#### 문제
+
+Kotlin에 TCP transport가 없다.
+
+#### 해결 방법
+
+Go의 `TcpClient`, `TcpServer`를 `java.net.Socket` / `ServerSocket` + coroutine으로 이식한다.
+
+**파일:**
+- `kotlin/src/main/kotlin/com/tokilabs/toki_socket/TcpClient.kt`
+- `kotlin/src/main/kotlin/com/tokilabs/toki_socket/TcpServer.kt`
+
+**TcpClient:**
+
+```kotlin
+class TcpClient private constructor(
+    private val socket: Socket,
+    intervalSec: Int,
+    waitSec: Int,
+) : BaseClient<TcpClient>(
+    self = /* 순환 참조 해결: lateinit + apply */ ...,
+    intervalSec = intervalSec,
+    waitSec = waitSec,
+    doClose = { socket.close() }
+) {
+    override val communicator: Communicator = Communicator(this, parserMap, scope)
+    private val writeMutex = Mutex()
+
+    // TCP Transport 구현
+    suspend fun writePacket(base: PacketBase) {
+        val bytes = base.toByteArray()
+        val header = ByteBuffer.allocate(4).putInt(bytes.size).array()
+        writeMutex.withLock {
+            withContext(Dispatchers.IO) {
+                socket.getOutputStream().write(header)
+                socket.getOutputStream().write(bytes)
+            }
+        }
+    }
+    fun closeTransport() { socket.close() }
+
+    private fun readLoop() {
+        scope.launch(Dispatchers.IO) {
+            val input = socket.getInputStream()
+            val header = ByteArray(4)
+            while (communicator.isAlive()) {
+                try {
+                    input.readFully(header)
+                    val length = ByteBuffer.wrap(header).int
+                    if (length == 0) continue
+                    if (length > MAX_PACKET_SIZE) { onDisconnected(); return@launch }
+                    val bytes = ByteArray(length)
+                    input.readFully(bytes)
+                    val base = PacketBase.parseFrom(bytes)
+                    communicator.onReceivedData(base.typeName, base.data.toByteArray(), base.nonce, base.responseNonce)
+                    sendHeartBeat()
+                } catch (e: Exception) {
+                    onDisconnected(); return@launch
+                }
+            }
+        }
+    }
+}
+```
+
+`InputStream.readFully`는 `java.io.DataInputStream` wrapping으로 구현 (`readFully` extension 함수 정의).
+
+**TcpServer:**
+
+Go의 `TcpServer`와 동일 구조. `ServerSocket.accept()`를 `Dispatchers.IO`에서 loop.
+
+```kotlin
+class TcpServer(
+    private val host: String,
+    private val port: Int,
+    private val newClient: (Socket) -> TcpClient,
+) {
+    private val scope = CoroutineScope(SupervisorJob() + Dispatchers.IO)
+    private val clients = CopyOnWriteArrayList<TcpClient>()
+    private var serverSocket: ServerSocket? = null
+    var onClientConnected: (TcpClient) -> Unit = {}
+
+    fun start() { ... }
+    fun stop() { ... }
+    fun broadcast(m: MessageLite) { ... }
+    fun clients(): List<TcpClient> { ... }
+}
+```
+
+#### 수정 파일 및 체크리스트
+
+- [ ] `TcpClient.kt` 생성
+  - [ ] `companion object { const val MAX_PACKET_SIZE = 64 * 1024 * 1024 }`
+  - [ ] `Transport` 구현: `writePacket` (4-byte BE header + proto bytes), `close`
+  - [ ] `readLoop()`: header 4바이트 읽기 → length=0 skip → length>MAX reject → bytes 읽기 → PacketBase.parseFrom → onReceivedData → sendHeartBeat
+  - [ ] `DialTcp(host, port, intervalSec, waitSec, parserMap)` 팩토리 함수
+  - [ ] HeartBeat 리스너 등록 (`communicator.addListener(HeartBeat typeName, ::onHeartBeat)`)
+  - [ ] WriteErrorHandler 등록 (`communicator.setWriteErrorHandler { onDisconnected() }`)
+- [ ] `TcpServer.kt` 생성
+  - [ ] `start()`: ServerSocket bind → accept loop (Dispatchers.IO)
+  - [ ] `stop()`: serverSocket.close() → clients 복사 후 전부 close
+  - [ ] `broadcast(m)`: clients 순회하여 send
+  - [ ] 클라이언트 disconnect 시 clients 리스트에서 제거 (addDisconnectListener 활용)
+
+#### 테스트 작성
+
+**파일:** `kotlin/src/test/kotlin/com/tokilabs/toki_socket/TcpTest.kt`
+
+| 테스트명 | 검증 목표 |
+|---------|---------|
+| `testTcpSendReceive` | client.send → server addListener 수신 |
+| `testTcpRequestResponse` | sendRequestTyped → index*2, "echo: msg" |
+| `testTcpBroadcast` | server.broadcast → 연결된 클라이언트 수신 |
+| `testTcpServerStopDisconnectsClients` | server.stop() → client disconnect 콜백 |
+| `testTcpClientCloseIdempotent` | close() 3회 호출 시 오류 없음 |
+
+#### 중간 검증
+
+```bash
+cd kotlin
+./gradlew test --tests "*.TcpTest"
+# 예상: 5개 테스트 PASS
+```
+
+---
+
+### [API-6] WsClient / WsServer 구현
+
+#### 문제
+
+Kotlin에 WebSocket transport가 없다.
+
+#### 해결 방법
+
+WebSocket 클라이언트는 OkHttp(`okhttp3.WebSocket`), 서버는 `org.java-websocket:Java-WebSocket`(`WebSocketServer`)을 사용한다. Android 호환을 위해 서버 쪽 `java-websocket`은 JVM 테스트/서버 전용으로 명시한다.
+
+**파일:**
+- `kotlin/src/main/kotlin/com/tokilabs/toki_socket/WsClient.kt`
+- `kotlin/src/main/kotlin/com/tokilabs/toki_socket/WsServer.kt`
+
+**WsClient (OkHttp 기반):**
+
+```kotlin
+class WsClient private constructor(
+    private val ws: okhttp3.WebSocket,
+    private val closeWs: () -> Unit,
+    intervalSec: Int,
+    waitSec: Int,
+    parserMap: ParserMap,
+) : BaseClient<WsClient>(...) {
+    override val communicator = Communicator(this /* as Transport */, parserMap, scope)
+
+    // Transport 구현
+    fun writePacket(base: PacketBase) {
+        val bytes = base.toByteArray()
+        ws.send(ByteString.of(*bytes))  // OkHttp binary frame
+    }
+
+    // OkHttp WebSocketListener (onMessage에서 onReceivedData 호출)
+}
+```
+
+OkHttp `WebSocket.send(ByteString)`은 thread-safe하므로 별도 writeMutex 불필요.
+
+**WsServer (Java-WebSocket 기반):**
+
+```kotlin
+class WsServer(host: String, port: Int) : org.java_websocket.server.WebSocketServer(...) {
+    val clients = CopyOnWriteArrayList<WsClient>()
+    var onClientConnected: (WsClient) -> Unit = {}
+
+    override fun onOpen(conn: WebSocket, handshake: ClientHandshake) { ... }
+    override fun onMessage(conn: WebSocket, bytes: ByteBuffer) { ... }
+    override fun onClose(...) { ... }
+    override fun onError(...) { ... }
+}
+```
+
+`java-websocket`의 `onMessage(conn, ByteBuffer)`로 binary frame을 수신하여 `PacketBase.parseFrom(bytes)` 후 해당 WsClient의 `communicator.onReceivedData(...)` 호출.
+
+#### 수정 파일 및 체크리스트
+
+- [ ] `WsClient.kt` 생성
+  - [ ] OkHttpClient + `Request.Builder().url(ws://...)` + `newWebSocket(request, listener)`
+  - [ ] `WebSocketListener.onMessage(ws, bytes: ByteString)`: PacketBase.parseFrom → onReceivedData → sendHeartBeat
+  - [ ] `WebSocketListener.onFailure(ws, t, response)`: onDisconnected
+  - [ ] `Transport.writePacket`: `ws.send(ByteString.of(*bytes))`
+  - [ ] `Transport.close`: `ws.close(1000, null)` + OkHttpClient.dispatcher.executorService.shutdown()
+  - [ ] HeartBeat 리스너 등록, WriteErrorHandler 등록
+  - [ ] `DialWs(host, port, path, intervalSec, waitSec, parserMap)` 팩토리
+  - [ ] `DialWss(host, port, path, sslContext, intervalSec, waitSec, parserMap)` 팩토리
+- [ ] `WsServer.kt` 생성
+  - [ ] `WebSocketServer` 상속, binary 프레임 처리
+  - [ ] WsClient 인스턴스 생성 및 clients 리스트 관리
+  - [ ] `start()` / `stop()` / `broadcast(m)`
+  - [ ] 클라이언트 disconnect 시 clients 리스트에서 제거
+
+#### 테스트 작성
+
+**파일:** `kotlin/src/test/kotlin/com/tokilabs/toki_socket/WsTest.kt`
+
+| 테스트명 | 검증 목표 |
+|---------|---------|
+| `testWsSendReceive` | client.send → server addListener 수신 |
+| `testWsRequestResponse` | sendRequestTyped → index*2, "echo: msg" |
+| `testWsBroadcast` | server.broadcast → 연결된 클라이언트 수신 |
+| `testWsServerStopDisconnectsClients` | server.stop() → client disconnect 콜백 |
+
+#### 중간 검증
+
+```bash
+cd kotlin
+./gradlew test --tests "*.WsTest"
+# 예상: 4개 테스트 PASS
+```
+
+---
+
+### [API-7] Heartbeat 통합 테스트
+
+#### 문제
+
+heartbeat 타이머가 비활성 구간 후 올바르게 발송되고, 응답 없을 때 disconnect를 트리거하는지 검증되지 않았다.
+
+#### 해결 방법
+
+Go의 `heartbeat_test.go` 패턴을 Kotlin coroutine 테스트로 이식한다. `runTest` + `TestCoroutineScheduler`로 실제 시간 대기 없이 가상 시간 진행.
+
+**파일:** `kotlin/src/test/kotlin/com/tokilabs/toki_socket/HeartbeatTest.kt`
+
+| 테스트명 | 검증 목표 |
+|---------|---------|
+| `testHeartbeatSentAfterInactivity` | intervalSec 경과 → HeartBeat 패킷 전송 확인 |
+| `testHeartbeatDisconnectOnNoResponse` | waitSec 경과 → onDisconnected 호출 확인 |
+| `testHeartbeatResetOnReceive` | 메시지 수신 → heartbeat 타이머 리셋 확인 |
+
+#### 수정 파일 및 체크리스트
+
+- [ ] `HeartbeatTest.kt` 생성 (위 3개 테스트)
+
+#### 테스트 작성
+
+본 항목 자체가 테스트 작성이다.
+
+#### 중간 검증
+
+```bash
+cd kotlin
+./gradlew test --tests "*.HeartbeatTest"
+# 예상: 3개 테스트 PASS
+```
+
+---
+
+### [API-8] Go ↔ Kotlin 크로스테스트
+
+#### 문제
+
+다른 언어 구현체와의 wire format 호환성이 검증되지 않았다.
+
+#### 해결 방법
+
+`skills/add-toki-socket-crosstest-language/SKILL.md`의 runner 배치 규칙을 따른다.
+
+**추가 파일:**
+
+| 파일 | 역할 |
+|------|------|
+| `go/crosstest/go_kotlin.go` | Go 서버 오케스트레이터 (Kotlin subprocess 실행) |
+| `kotlin/crosstest/go_kotlin_client/Main.kt` | Kotlin subprocess (Go 서버에 접속) |
+| `kotlin/crosstest/kotlin_go.kt` | Kotlin 서버 오케스트레이터 (Go subprocess 실행) |
+| `go/crosstest/kotlin_go_client/main.go` | Go subprocess (Kotlin 서버에 접속) |
+
+**포트 배정 (기존과 충돌 없음):**
+
+```
+Go server / Kotlin client TCP:     29290
+Go server / Kotlin client WS:      29292
+Kotlin server / Go client TCP:     29390
+Kotlin server / Go client WS:      29392
+```
+
+기존 포트 (충돌 없음 확인):
+- 29090 (Dart server / Go client TCP)
+- 29092 (Dart server / Go client WS)
+- 29190 (Go server / Dart client TCP)
+- 29192 (Go server / Dart client WS)
+
+**시나리오 (TCP + WebSocket 각각):**
+
+| 시나리오 | 내용 |
+|---------|------|
+| 1 | 클라이언트 fire-and-forget `TestData(index=101, message="fire from kotlin client")` → 서버 검증 |
+| 2 | 서버 push `TestData(index=200, message="push from go server")` → 클라이언트 검증 |
+| 3 | 클라이언트 `sendRequest` → 응답 `index=req.index*2`, `message="echo: req.message"` |
+| 4 | 동시 5개 `sendRequest` → responseNonce 라우팅 검증 |
+
+send-push/requests 페이즈 분리 패턴은 Go ↔ Dart 크로스테스트와 동일하게 적용한다.
+
+**`kotlin/crosstest/go_kotlin_client/Main.kt` 실행 방법:**
+
+```bash
+cd kotlin
+./gradlew run --args="--mode=tcp --port=29290 --phase=send-push"
+```
+
+`build.gradle.kts`에 `application { mainClass.set("com.tokilabs.toki_socket.crosstest.MainKt") }` 추가 필요.
+
+**`go/crosstest/go_kotlin.go` 실행 방법:**
+
+```bash
+cd go
+go run ./crosstest/go_kotlin.go
+```
+
+#### 수정 파일 및 체크리스트
+
+- [ ] `go/crosstest/go_kotlin.go` 생성
+  - [ ] TCP send-push (port 29290), TCP requests, WS send-push (port 29292), WS requests
+  - [ ] Kotlin subprocess 실행: `./gradlew run --args="..."` (kotlin dir 기준)
+  - [ ] `validateResultLines` 활용 (go_dart.go와 동일 헬퍼)
+- [ ] `kotlin/crosstest/go_kotlin_client/Main.kt` 생성
+  - [ ] `INFO typeName kotlin=TestData` 출력
+  - [ ] `--mode`, `--port`, `--phase` 인수 파싱
+  - [ ] send-push: TestData 전송 (시나리오 1) + 서버 push 수신 (시나리오 2)
+  - [ ] requests: 단일 request (시나리오 3) + 5개 concurrent request (시나리오 4)
+  - [ ] `PASS scenario=N detail=...` / `FAIL scenario=N error=...` 출력
+- [ ] `kotlin/crosstest/kotlin_go.kt` 생성 (Kotlin 서버 오케스트레이터)
+  - [ ] TCP 서버 (29390) + WS 서버 (29392) 시작
+  - [ ] Go subprocess 실행: `go run ./crosstest/kotlin_go_client`
+  - [ ] PASS/FAIL 파싱 및 검증
+- [ ] `go/crosstest/kotlin_go_client/main.go` 생성
+  - [ ] Kotlin 서버에 접속하는 Go 클라이언트 (dart_go_client/main.go와 동일 구조)
+  - [ ] `INFO typeName go=TestData` 출력
+  - [ ] 동일 4개 시나리오
+
+#### 테스트 작성
+
+본 항목 자체가 크로스테스트이다.
+
+#### 중간 검증
+
+```bash
+# Go 서버 ↔ Kotlin 클라이언트
+cd go && go run ./crosstest/go_kotlin.go
+# 예상: PASS all go-server/kotlin-client crosstests passed
+
+# Kotlin 서버 ↔ Go 클라이언트
+cd kotlin && ./gradlew run -PmainClass=com.tokilabs.toki_socket.crosstest.KotlinGoKt
+# 또는
+cd kotlin && kotlinc -script crosstest/kotlin_go.kts
+# 예상: PASS all kotlin-server/go-client crosstests passed
+```
+
+---
+
+## 수정 파일 요약
+
+| 파일 | 항목 |
+|------|------|
+| `kotlin/settings.gradle.kts` | API-1 |
+| `kotlin/build.gradle.kts` | API-1 |
+| `kotlin/src/main/proto/message_common.proto` | API-1 |
+| `kotlin/src/main/kotlin/.../Communicator.kt` | API-2 |
+| `kotlin/src/test/kotlin/.../CommunicatorTest.kt` | API-2 |
+| `kotlin/src/main/kotlin/.../HeartbeatTimer.kt` | API-3 |
+| `kotlin/src/test/kotlin/.../HeartbeatTimerTest.kt` | API-3 |
+| `kotlin/src/main/kotlin/.../BaseClient.kt` | API-4 |
+| `kotlin/src/main/kotlin/.../TcpClient.kt` | API-5 |
+| `kotlin/src/main/kotlin/.../TcpServer.kt` | API-5 |
+| `kotlin/src/test/kotlin/.../TcpTest.kt` | API-5 |
+| `kotlin/src/main/kotlin/.../WsClient.kt` | API-6 |
+| `kotlin/src/main/kotlin/.../WsServer.kt` | API-6 |
+| `kotlin/src/test/kotlin/.../WsTest.kt` | API-6 |
+| `kotlin/src/test/kotlin/.../HeartbeatTest.kt` | API-7 |
+| `go/crosstest/go_kotlin.go` | API-8 |
+| `kotlin/crosstest/go_kotlin_client/Main.kt` | API-8 |
+| `kotlin/crosstest/kotlin_go.kt` | API-8 |
+| `go/crosstest/kotlin_go_client/main.go` | API-8 |
+| `PROTOCOL.md` | Kotlin 행 status 업데이트 |
+| `README.md` | Kotlin 행 status 업데이트 |
+
+---
+
+## 최종 검증
+
+```bash
+# 1. Kotlin 단위 테스트 전체
+cd kotlin
+./gradlew test
+# 예상: 모든 테스트 PASS, BUILD SUCCESSFUL
+
+# 2. Go 단위 테스트 (크로스테스트 헬퍼 추가로 인한 회귀 없음)
+cd go
+go test ./...
+# 예상: ok toki-labs.com/toki_socket/go [no test files changed]
+
+# 3. Kotlin linter
+cd kotlin
+./gradlew ktlintCheck   # ktlint plugin 추가 시
+# 예상: BUILD SUCCESSFUL
+
+# 4. Go 서버 ↔ Kotlin 클라이언트 크로스테스트
+cd go
+go run ./crosstest/go_kotlin.go
+# 예상: PASS all go-server/kotlin-client crosstests passed
+
+# 5. Kotlin 서버 ↔ Go 클라이언트 크로스테스트
+cd kotlin
+./gradlew run -PmainClass=com.tokilabs.toki_socket.crosstest.KotlinGoKt
+# 예상: PASS all kotlin-server/go-client crosstests passed
+
+# 6. proto 동기화 검증
+tools/check_proto_sync.sh
+# 예상: no diff
+```
--- a/tasks/kotlin_impl/plan_1.log
+++ b/tasks/kotlin_impl/plan_1.log
@ -0,0 +1,396 @@
+<!-- task=kotlin_impl plan=1 tag=REVIEW_API -->
+
+# Kotlin 구현 후속 수정 — WARN 항목 해소
+
+## 이 파일을 읽는 구현 에이전트에게
+
+각 항목의 체크리스트를 완료 처리하고, 중간 검증 명령을 실제로 실행한 뒤 출력을 `CODE_REVIEW.md`의 `검증 결과` 섹션에 붙여 넣으세요.
+계획과 다르게 구현한 부분이 있으면 `계획 대비 변경 사항`에 이유와 함께 기록하세요.
+
+---
+
+## 배경
+
+`plan_0.log` 의 WARN 판정에서 발견된 4개 Suggested 항목을 수정한다. Required 항목은 없었고, Nit 1개(`Communicator.parse()` visibility)는 아래 포함한다. JVM 환경 부재로 인한 Gradle 미검증 상태는 이 항목들과 무관하므로 별도 다루지 않는다.
+
+---
+
+## 의존 관계 및 구현 순서
+
+REVIEW_API-1 → REVIEW_API-2 (sourceset 변경이 선행돼야 kotlin 빌드 구조에서 REVIEW_API-3, 4 검증 가능) → REVIEW_API-3, REVIEW_API-4 (병렬 가능)
+
+---
+
+### [REVIEW_API-1] `WsServer.stop()` — `InterruptedException` 미처리 수정
+
+#### 문제
+
+`kotlin/src/main/kotlin/com/tokilabs/toki_socket/WsServer.kt:41`
+
+`super.stop(1000)` 은 `WebSocketServer.stop(int)` 로, Java 검사 예외 `InterruptedException` 을 선언한다. `runBlocking` 내에서 호출될 때 이 예외가 전파되면 현재 coroutine이 취소 신호로 처리하여 `stop()` 이후 정리 코드가 실행되지 않을 수 있다.
+
+#### 해결 방법
+
+`super.stop(1000)` 을 `runCatching` 으로 감싼다.
+
+**Before (`WsServer.kt:36-41`):**
+```kotlin
+override fun stop() {
+    if (!startedFlag.compareAndSet(true, false)) return
+    val snapshot = clients.toList()
+    clients.clear()
+    snapshot.forEach { it.close() }
+    super.stop(1000)
+}
+```
+
+**After:**
+```kotlin
+override fun stop() {
+    if (!startedFlag.compareAndSet(true, false)) return
+    val snapshot = clients.toList()
+    clients.clear()
+    snapshot.forEach { it.close() }
+    runCatching { super.stop(1000) }
+}
+```
+
+#### 수정 파일 및 체크리스트
+
+- [x] `kotlin/src/main/kotlin/com/tokilabs/toki_socket/WsServer.kt` — `super.stop(1000)` → `runCatching { super.stop(1000) }`
+
+#### 테스트 작성
+
+SKIP — 기존 `WsTest.testWsServerStopDisconnectsClients` 가 stop 경로를 커버한다. `InterruptedException` 을 강제로 발생시키는 단위 테스트는 `java-websocket` 내부 구현 의존성이 높아 추가하지 않는다.
+
+#### 중간 검증
+
+```bash
+cd kotlin
+./gradlew compileKotlin
+# 예상: BUILD SUCCESSFUL
+```
+
+---
+
+### [REVIEW_API-2] `crosstest/` 를 main sourceset에서 분리
+
+#### 문제
+
+`kotlin/build.gradle.kts:14`
+
+```kotlin
+named("main") {
+    kotlin.srcDir("crosstest")
+}
+```
+
+`kotlin_go.kt`, `go_kotlin_client/Main.kt` 가 라이브러리 main sourceset에 포함되어 프로덕션 JAR에 crosstest 코드가 실린다.
+
+#### 해결 방법
+
+`build.gradle.kts` 에서 `crosstest` 를 sourceSets.main 에서 제거하고, 대신 별도 `crosstest` sourceset 을 정의한다. `application` 플러그인의 `mainClass` 는 기본값을 크로스테스트 runner로 유지하되 `crosstest` sourceset을 통해 공급한다.
+
+**Before (`build.gradle.kts:10-17`):**
+```kotlin
+kotlin {
+    jvmToolchain(17)
+    sourceSets {
+        named("main") {
+            kotlin.srcDir("crosstest")
+        }
+    }
+}
+```
+
+**After:**
+```kotlin
+kotlin {
+    jvmToolchain(17)
+}
+
+sourceSets {
+    create("crosstest") {
+        kotlin.srcDir("crosstest")
+        compileClasspath += sourceSets["main"].output + configurations["runtimeClasspath"]
+        runtimeClasspath += output + compileClasspath
+    }
+}
+```
+
+`application` 블록의 `mainClass` 는 `crosstest` sourceset의 classpath 에서 로드되도록 `run` task를 재구성한다.
+
+**Before (`build.gradle.kts:42-47`):**
+```kotlin
+application {
+    mainClass.set(
+        (findProperty("mainClass") as String?)
+            ?: "com.tokilabs.toki_socket.crosstest.MainKt",
+    )
+}
+```
+
+**After:**
+```kotlin
+val crosstestSourceSet = sourceSets["crosstest"]
+
+tasks.named<JavaExec>("run") {
+    classpath = crosstestSourceSet.runtimeClasspath
+    mainClass.set(
+        (findProperty("mainClass") as String?)
+            ?: "com.tokilabs.toki_socket.crosstest.MainKt",
+    )
+}
+```
+
+#### 수정 파일 및 체크리스트
+
+- [x] `kotlin/build.gradle.kts` — `sourceSets.main.kotlin.srcDir("crosstest")` 제거
+- [x] `kotlin/build.gradle.kts` — `crosstest` sourceset 정의 추가
+- [x] `kotlin/build.gradle.kts` — `tasks.named<JavaExec>("run")` 블록에서 classpath를 `crosstestSourceSet.runtimeClasspath` 로 지정
+- [x] `kotlin/build.gradle.kts` — `kotlin { sourceSets { named("main") { ... } } }` 블록 제거 또는 빈 상태로 정리
+
+#### 테스트 작성
+
+SKIP — 빌드 구조 변경이므로 컴파일 성공으로 충분하다.
+
+#### 중간 검증
+
+```bash
+cd kotlin
+./gradlew compileKotlin compileCrosstestKotlin
+# 예상: BUILD SUCCESSFUL
+# crosstest 클래스가 main JAR에 포함되지 않는지 확인:
+./gradlew jar
+jar tf build/libs/toki-socket-kotlin-0.1.0.jar | grep crosstest
+# 예상: 출력 없음 (crosstest 클래스 미포함)
+```
+
+---
+
+### [REVIEW_API-3] `kotlin_go.kt` listener 내 `runBlocking` 제거
+
+#### 문제
+
+`kotlin/crosstest/kotlin_go.kt:56-63`, `104-111`
+
+`addListenerTyped` 의 callback은 `TcpClient.readLoop` 의 `Dispatchers.IO` coroutine에서 동기 호출된다. 여기서 `runBlocking { client.send(...) }` 를 호출하면 IO 스레드를 블로킹한다.
+
+#### 해결 방법
+
+`runBlocking { ... }` 을 `scope.launch { ... }` 로 교체한다. `kotlin_go.kt` 파일은 `runBlocking` scope 안에서 실행되므로, 서버 scope를 직접 사용하거나 `GlobalScope` 대신 로컬 `CoroutineScope` 를 생성한다. 가장 단순한 방법은 listener에서 별도 coroutine을 시작한다.
+
+**Before (`kotlin_go.kt:51-63`):**
+```kotlin
+server.onClientConnected = { client ->
+    addListenerTyped<TestData>(client.communicator) { data ->
+        println("SERVER_RECEIVED index=${data.index} message=${data.message}")
+        val valid = data.index == 101 && data.message == "fire from go client"
+        received.complete(valid)
+        if (valid) {
+            runBlocking {
+                client.send(
+                    TestData.newBuilder()
+                        .setIndex(200)
+                        .setMessage("push from kotlin server")
+                        .build(),
+                )
+            }
+        }
+    }
+}
+```
+
+**After:**
+```kotlin
+server.onClientConnected = { client ->
+    addListenerTyped<TestData>(client.communicator) { data ->
+        println("SERVER_RECEIVED index=${data.index} message=${data.message}")
+        val valid = data.index == 101 && data.message == "fire from go client"
+        received.complete(valid)
+        if (valid) {
+            client.communicator.scope.launch {
+                client.send(
+                    TestData.newBuilder()
+                        .setIndex(200)
+                        .setMessage("push from kotlin server")
+                        .build(),
+                )
+            }
+        }
+    }
+}
+```
+
+단, `Communicator.scope` 가 현재 `private` 이다. `BaseClient.scope` 가 `protected` 이므로, `kotlin_go.kt` 에서 접근 가능한 방법이 필요하다. `TcpClient` 가 `BaseClient` 를 상속하므로 `client.scope` (protected)를 `internal` 또는 직접 접근 가능한 방식으로 노출하거나, `client.communicator` 를 통해 접근하는 대신 `kotlinx.coroutines.GlobalScope` 를 임시 사용한다.
+
+가장 깔끔한 방법: `BaseClient` 의 `scope` 를 `internal` 로 노출하여 같은 모듈 내 crosstest 코드에서 사용 가능하게 한다.
+
+**`BaseClient.kt` 변경:**
+```kotlin
+// Before
+protected val scope = CoroutineScope(SupervisorJob() + Dispatchers.IO)
+
+// After
+internal val scope = CoroutineScope(SupervisorJob() + Dispatchers.IO)
+```
+
+`kotlin_go.kt` 의 `runBlocking { client.send(...) }` 두 곳 (TCP send-push:56-63, WS send-push:104-111) 을 `client.scope.launch { client.send(...) }` 로 교체한다.
+
+#### 수정 파일 및 체크리스트
+
+- [x] `kotlin/src/main/kotlin/com/tokilabs/toki_socket/BaseClient.kt` — `scope` 를 `protected` → `internal` 로 변경
+- [x] `kotlin/crosstest/kotlin_go.kt:56-63` — `runBlocking { client.send(...) }` → `coroutineScope` 의 `launch { client.send(...) }`
+- [x] `kotlin/crosstest/kotlin_go.kt:104-111` — 동일 변경
+
+#### 테스트 작성
+
+SKIP — crosstest 코드 수정이고 기능 변경이 없다. 크로스테스트 자체가 검증이다.
+
+#### 중간 검증
+
+```bash
+cd kotlin
+./gradlew compileCrosstestKotlin
+# 예상: BUILD SUCCESSFUL (runBlocking 제거로 인한 compile error 없음)
+```
+
+---
+
+### [REVIEW_API-4] `HeartbeatTest.testHeartbeatResetOnReceive()` — 수신 경로 검증 추가
+
+#### 문제
+
+`kotlin/src/test/kotlin/com/tokilabs/toki_socket/HeartbeatTest.kt:69-81`
+
+현재 테스트는 `sendHeartBeat()` 를 두 번 직접 호출한다. 실제 경로인 `communicator.onReceivedData()` → `sendHeartBeat()` 를 거쳐 타이머가 리셋되는지 검증하지 않는다.
+
+#### 해결 방법
+
+기존 테스트를 두 개로 분리한다:
+1. `testHeartbeatTimerResetBySendHeartBeat` — 기존 로직 유지 (sendHeartBeat 재호출 → 타이머 리셋)
+2. `testHeartbeatTimerResetOnReceivedData` — `communicator.onReceivedData()` 를 호출한 뒤 heartbeat가 지연되는지 확인
+
+**새 테스트 (`testHeartbeatTimerResetOnReceivedData`):**
+
+```kotlin
+@Test
+fun testHeartbeatTimerResetOnReceivedData() = runBlocking {
+    val transport = HeartbeatTransport()
+    val client = HeartbeatClient(transport, 1, 1)
+    var received = false
+    client.communicator.addListener(typeNameOf(testData())) {
+        received = true
+    }
+
+    client.sendHeartBeat()
+    delay(700)
+    // 데이터 수신 시뮬레이션 — readLoop가 onReceivedData 후 sendHeartBeat() 호출하는 경로
+    client.communicator.onReceivedData(typeNameOf(testData()), testData().toByteArray(), incomingNonce = 1)
+    assertTrue(received)
+    client.sendHeartBeat()  // readLoop가 호출하는 sendHeartBeat()
+    delay(500)
+    assertTrue(transport.packets.none { it.typeName == typeNameOf<HeartBeat>() })
+    delay(700)
+    assertTrue(transport.packets.any { it.typeName == typeNameOf<HeartBeat>() })
+    client.close()
+}
+```
+
+`testData()` 헬퍼: `TestHelpers.kt` 에 `fun testData() = TestData.newBuilder().setIndex(1).setMessage("ping").build()` 추가.
+
+`HeartbeatClient` 의 `communicator` parserMap 에 `TestData` 가 포함되도록 `testParserMap()` 을 사용한다. 테스트에서는 `TestData` 리스너를 등록하고 `received` 를 확인해 `onReceivedData()` 가 listener dispatch까지 실제로 진행됐는지 검증한다.
+
+#### 수정 파일 및 체크리스트
+
+- [x] `kotlin/src/test/kotlin/com/tokilabs/toki_socket/HeartbeatTest.kt` — `testHeartbeatResetOnReceive` 를 `testHeartbeatTimerResetBySendHeartBeat` 로 rename
+- [x] `kotlin/src/test/kotlin/com/tokilabs/toki_socket/HeartbeatTest.kt` — `testHeartbeatTimerResetOnReceivedData` 테스트 추가
+- [x] `kotlin/src/test/kotlin/com/tokilabs/toki_socket/TestHelpers.kt` — `fun testData()` 헬퍼 추가
+
+#### 테스트 작성
+
+본 항목이 테스트 추가이다.
+
+#### 중간 검증
+
+```bash
+cd kotlin
+./gradlew test --tests "*.HeartbeatTest"
+# 예상: 4개 테스트 PASS (기존 3개 + 신규 1개)
+```
+
+---
+
+### [REVIEW_API-5] `Communicator.parse()` visibility — `internal` 로 제한 (Nit)
+
+#### 문제
+
+`kotlin/src/main/kotlin/com/tokilabs/toki_socket/Communicator.kt:266`
+
+`parse()` 가 `public` 으로 노출되어 있다. Go 의 `parse` 는 unexported이다. inline helper들은 `parse()` 를 직접 호출하지 않는다.
+
+#### 해결 방법
+
+```kotlin
+// Before
+fun parse(typeName: String, data: ByteArray): MessageLite {
+
+// After
+internal fun parse(typeName: String, data: ByteArray): MessageLite {
+```
+
+#### 수정 파일 및 체크리스트
+
+- [x] `kotlin/src/main/kotlin/com/tokilabs/toki_socket/Communicator.kt:266` — `fun parse` → `internal fun parse`
+
+#### 테스트 작성
+
+SKIP — `CommunicatorTest` 는 `parse()` 를 직접 호출하지 않는다. 같은 모듈이므로 `internal` 후에도 테스트 접근 가능하다.
+
+#### 중간 검증
+
+```bash
+cd kotlin
+./gradlew compileKotlin compileTestKotlin
+# 예상: BUILD SUCCESSFUL
+```
+
+---
+
+## 수정 파일 요약
+
+| 파일 | 항목 |
+|------|------|
+| `kotlin/src/main/kotlin/com/tokilabs/toki_socket/WsServer.kt` | REVIEW_API-1 |
+| `kotlin/build.gradle.kts` | REVIEW_API-2 |
+| `kotlin/src/main/kotlin/com/tokilabs/toki_socket/BaseClient.kt` | REVIEW_API-3 |
+| `kotlin/crosstest/kotlin_go.kt` | REVIEW_API-3 |
+| `kotlin/src/main/kotlin/com/tokilabs/toki_socket/WsClient.kt` | REVIEW_API-3 follow-up: crosstest sourceset에서 server factory 접근 가능하도록 공개 |
+| `kotlin/src/test/kotlin/com/tokilabs/toki_socket/HeartbeatTest.kt` | REVIEW_API-4 |
+| `kotlin/src/test/kotlin/com/tokilabs/toki_socket/TestHelpers.kt` | REVIEW_API-4 |
+| `kotlin/src/test/kotlin/com/tokilabs/toki_socket/TcpTest.kt` | 최종 검증 follow-up: blocking accept를 `Dispatchers.IO`로 이동 |
+| `kotlin/src/main/kotlin/com/tokilabs/toki_socket/Communicator.kt` | REVIEW_API-5 |
+
+---
+
+## 최종 검증
+
+```bash
+# 1. Kotlin 전체 단위 테스트
+cd kotlin
+./gradlew test
+# 예상: 모든 테스트 PASS (HeartbeatTest 4개 포함)
+
+# 2. JAR에 crosstest 미포함 확인
+./gradlew jar
+jar tf build/libs/toki-socket-kotlin-0.1.0.jar | grep crosstest
+# 예상: 출력 없음
+
+# 3. Go 단위 테스트 회귀 없음
+cd ../go && go test ./...
+# 예상: ok toki-labs.com/toki_socket/go/test
+
+# 4. proto 동기화
+cd .. && bash tools/check_proto_sync.sh
+# 예상: Proto schemas are in sync.
+```
--- a/tools/check_proto_sync.sh
+++ b/tools/check_proto_sync.sh
@ -4,6 +4,7 @@ set -euo pipefail
 repo_root="$(cd "$(dirname "${BASH_SOURCE[0]}")/.." && pwd)"
 dart_proto="$repo_root/dart/lib/src/packets/message_common.proto"
 go_proto="$repo_root/go/packets/message_common.proto"
+kotlin_proto="$repo_root/kotlin/src/main/proto/message_common.proto"

 if [[ ! -f "$dart_proto" ]]; then
  echo "Missing canonical Dart proto: $dart_proto" >&2
@ -15,12 +16,20 @@ if [[ ! -f "$go_proto" ]]; then
  exit 1
 fi

+if [[ -d "$repo_root/kotlin" && ! -f "$kotlin_proto" ]]; then
+  echo "Missing Kotlin proto copy: $kotlin_proto" >&2
+  exit 1
+fi
+
 tmp_dir="$(mktemp -d)"
 trap 'rm -rf "$tmp_dir"' EXIT

 normalize_proto() {
  awk '
    /^[[:space:]]*option go_package[[:space:]]*=.*;[[:space:]]*$/ { next }
+    /^[[:space:]]*option java_package[[:space:]]*=.*;[[:space:]]*$/ { next }
+    /^[[:space:]]*option java_outer_classname[[:space:]]*=.*;[[:space:]]*$/ { next }
+    /^[[:space:]]*option java_multiple_files[[:space:]]*=.*;[[:space:]]*$/ { next }
    /^[[:space:]]*$/ { next }
    { print }
  ' "$1"
@ -28,6 +37,9 @@ normalize_proto() {

 normalize_proto "$dart_proto" >"$tmp_dir/dart.proto"
 normalize_proto "$go_proto" >"$tmp_dir/go.proto"
+if [[ -f "$kotlin_proto" ]]; then
+  normalize_proto "$kotlin_proto" >"$tmp_dir/kotlin.proto"
+fi

 if ! cmp -s "$tmp_dir/dart.proto" "$tmp_dir/go.proto"; then
  echo "Proto schema mismatch: go/packets/message_common.proto must match the Dart canonical proto except option go_package." >&2
@ -35,4 +47,10 @@ if ! cmp -s "$tmp_dir/dart.proto" "$tmp_dir/go.proto"; then
  exit 1
 fi

+if [[ -f "$tmp_dir/kotlin.proto" ]] && ! cmp -s "$tmp_dir/dart.proto" "$tmp_dir/kotlin.proto"; then
+  echo "Proto schema mismatch: kotlin/src/main/proto/message_common.proto must match the Dart canonical proto except Java options." >&2
+  diff -u "$tmp_dir/dart.proto" "$tmp_dir/kotlin.proto" >&2
+  exit 1
+fi
+
 echo "Proto schemas are in sync."