feat(server): carry latencyMs + totalTokens through ServerMessage.ChatTurn

ChatTurn wire frame now includes latencyMs: Long? and totalTokens: Int?.
DomainEventMapper reads them from ChatTurnEvent.latencyMs and
tokensUsed?.totalTokens. Positional call site in DomainEventMapperTest
converted to named args. Two new serialization tests cover the ROUTER
(metrics present) and USER (metrics absent) paths.

apps/server/src/main/kotlin/com/correx/apps/server/bridge/DomainEventMapper.kt

@@ -82,6 +82,8 @@ suspend fun domainEventToServerMessage(
             turnId = p.turnId,
             role = p.role.name,
             content = p.content,
+            latencyMs = p.latencyMs,
+            totalTokens = p.tokensUsed?.totalTokens,
             sequence = seq,
             sessionSequence = sessionSequence,
         )

apps/server/src/main/kotlin/com/correx/apps/server/protocol/ServerMessage.kt

@@ -67,6 +67,8 @@ sealed interface ServerMessage {
         val turnId: String,
         val role: String,
         val content: String,
+        val latencyMs: Long? = null,
+        val totalTokens: Int? = null,
         override val sequence: Long,
         override val sessionSequence: Long,
     ) : ServerMessage, SessionMessage

apps/server/src/test/kotlin/com/correx/apps/server/bridge/DomainEventMapperTest.kt

@@ -113,7 +113,14 @@ class DomainEventMapperTest {
         )
         val result = domainEventToServerMessage(event, noopStore, sessionSequence = 3L)
         assertEquals(
-            ServerMessage.ChatTurn(sessionId, "turn-1", "ROUTER", "hello", event.sequence, 3L),
+            ServerMessage.ChatTurn(
+                sessionId = sessionId,
+                turnId = "turn-1",
+                role = "ROUTER",
+                content = "hello",
+                sequence = event.sequence,
+                sessionSequence = 3L,
+            ),
             result,
         )
     }

apps/server/src/test/kotlin/com/correx/apps/server/protocol/ServerMessageSerializationTest.kt

@@ -45,6 +45,40 @@ class ServerMessageSerializationTest {
         assert(jsonStr.contains("\"content\":\"hi there\"")) { "expected content" }
     }
 
+    @Test
+    fun `ChatTurn with metrics encodes latencyMs and totalTokens`() {
+        val msg = ServerMessage.ChatTurn(
+            sessionId = SessionId("sess-1"),
+            turnId = "t9",
+            role = "ROUTER",
+            content = "hi",
+            latencyMs = 3000,
+            totalTokens = 943,
+            sequence = 7,
+            sessionSequence = 2,
+        )
+        val jsonStr = ProtocolSerializer.encodeServerMessage(msg)
+        assert(jsonStr.contains("\"type\":\"chat.turn\"")) { "expected type=chat.turn" }
+        assert(jsonStr.contains("\"latencyMs\":3000")) { "expected latencyMs=3000" }
+        assert(jsonStr.contains("\"totalTokens\":943")) { "expected totalTokens=943" }
+    }
+
+    @Test
+    fun `ChatTurn without metrics encodes latencyMs and totalTokens as absent or null`() {
+        val msg = ServerMessage.ChatTurn(
+            sessionId = SessionId("sess-1"),
+            turnId = "t10",
+            role = "USER",
+            content = "hello",
+            sequence = 8,
+            sessionSequence = 3,
+        )
+        val jsonStr = ProtocolSerializer.encodeServerMessage(msg)
+        assert(jsonStr.contains("\"type\":\"chat.turn\"")) { "expected type=chat.turn" }
+        assert(!jsonStr.contains("\"latencyMs\":3000")) { "latencyMs should not be 3000" }
+        assert(!jsonStr.contains("\"totalTokens\":943")) { "totalTokens should not be 943" }
+    }
+
     @Test
     fun `SnapshotComplete encodes with only type field`() {
         val msg = ServerMessage.SnapshotComplete