Implement token usage from session-usage rfd

acp-model/api/acp-model.api

@@ -4885,15 +4885,17 @@ public final class com/agentclientprotocol/model/PromptRequest$Companion {
 
 public final class com/agentclientprotocol/model/PromptResponse : com/agentclientprotocol/model/AcpResponse {
 	public static final field Companion Lcom/agentclientprotocol/model/PromptResponse$Companion;
-	public synthetic fun <init> (Lcom/agentclientprotocol/model/StopReason;Ljava/lang/String;Lkotlinx/serialization/json/JsonElement;ILkotlin/jvm/internal/DefaultConstructorMarker;)V
-	public synthetic fun <init> (Lcom/agentclientprotocol/model/StopReason;Ljava/lang/String;Lkotlinx/serialization/json/JsonElement;Lkotlin/jvm/internal/DefaultConstructorMarker;)V
+	public synthetic fun <init> (Lcom/agentclientprotocol/model/StopReason;Ljava/lang/String;Lcom/agentclientprotocol/model/Usage;Lkotlinx/serialization/json/JsonElement;ILkotlin/jvm/internal/DefaultConstructorMarker;)V
+	public synthetic fun <init> (Lcom/agentclientprotocol/model/StopReason;Ljava/lang/String;Lcom/agentclientprotocol/model/Usage;Lkotlinx/serialization/json/JsonElement;Lkotlin/jvm/internal/DefaultConstructorMarker;)V
 	public final fun component1 ()Lcom/agentclientprotocol/model/StopReason;
 	public final fun component2-f2XpNSU ()Ljava/lang/String;
-	public final fun component3 ()Lkotlinx/serialization/json/JsonElement;
-	public final fun copy-5MJPFCQ (Lcom/agentclientprotocol/model/StopReason;Ljava/lang/String;Lkotlinx/serialization/json/JsonElement;)Lcom/agentclientprotocol/model/PromptResponse;
-	public static synthetic fun copy-5MJPFCQ$default (Lcom/agentclientprotocol/model/PromptResponse;Lcom/agentclientprotocol/model/StopReason;Ljava/lang/String;Lkotlinx/serialization/json/JsonElement;ILjava/lang/Object;)Lcom/agentclientprotocol/model/PromptResponse;
+	public final fun component3 ()Lcom/agentclientprotocol/model/Usage;
+	public final fun component4 ()Lkotlinx/serialization/json/JsonElement;
+	public final fun copy-hdWohc0 (Lcom/agentclientprotocol/model/StopReason;Ljava/lang/String;Lcom/agentclientprotocol/model/Usage;Lkotlinx/serialization/json/JsonElement;)Lcom/agentclientprotocol/model/PromptResponse;
+	public static synthetic fun copy-hdWohc0$default (Lcom/agentclientprotocol/model/PromptResponse;Lcom/agentclientprotocol/model/StopReason;Ljava/lang/String;Lcom/agentclientprotocol/model/Usage;Lkotlinx/serialization/json/JsonElement;ILjava/lang/Object;)Lcom/agentclientprotocol/model/PromptResponse;
 	public fun equals (Ljava/lang/Object;)Z
 	public final fun getStopReason ()Lcom/agentclientprotocol/model/StopReason;
+	public final fun getUsage ()Lcom/agentclientprotocol/model/Usage;
 	public final fun getUserMessageId-f2XpNSU ()Ljava/lang/String;
 	public fun get_meta ()Lkotlinx/serialization/json/JsonElement;
 	public fun hashCode ()I
@@ -7483,6 +7485,46 @@ public final class com/agentclientprotocol/model/UrlElicitationRequiredItem$Comp
 	public final fun serializer ()Lkotlinx/serialization/KSerializer;
 }
 
+public final class com/agentclientprotocol/model/Usage : com/agentclientprotocol/model/AcpWithMeta {
+	public static final field Companion Lcom/agentclientprotocol/model/Usage$Companion;
+	public fun <init> (JJJLjava/lang/Long;Ljava/lang/Long;Ljava/lang/Long;Lkotlinx/serialization/json/JsonElement;)V
+	public synthetic fun <init> (JJJLjava/lang/Long;Ljava/lang/Long;Ljava/lang/Long;Lkotlinx/serialization/json/JsonElement;ILkotlin/jvm/internal/DefaultConstructorMarker;)V
+	public final fun component1 ()J
+	public final fun component2 ()J
+	public final fun component3 ()J
+	public final fun component4 ()Ljava/lang/Long;
+	public final fun component5 ()Ljava/lang/Long;
+	public final fun component6 ()Ljava/lang/Long;
+	public final fun component7 ()Lkotlinx/serialization/json/JsonElement;
+	public final fun copy (JJJLjava/lang/Long;Ljava/lang/Long;Ljava/lang/Long;Lkotlinx/serialization/json/JsonElement;)Lcom/agentclientprotocol/model/Usage;
+	public static synthetic fun copy$default (Lcom/agentclientprotocol/model/Usage;JJJLjava/lang/Long;Ljava/lang/Long;Ljava/lang/Long;Lkotlinx/serialization/json/JsonElement;ILjava/lang/Object;)Lcom/agentclientprotocol/model/Usage;
+	public fun equals (Ljava/lang/Object;)Z
+	public final fun getCachedReadTokens ()Ljava/lang/Long;
+	public final fun getCachedWriteTokens ()Ljava/lang/Long;
+	public final fun getInputTokens ()J
+	public final fun getOutputTokens ()J
+	public final fun getThoughtTokens ()Ljava/lang/Long;
+	public final fun getTotalTokens ()J
+	public fun get_meta ()Lkotlinx/serialization/json/JsonElement;
+	public fun hashCode ()I
+	public fun toString ()Ljava/lang/String;
+}
+
+public final synthetic class com/agentclientprotocol/model/Usage$$serializer : kotlinx/serialization/internal/GeneratedSerializer {
+	public static final field INSTANCE Lcom/agentclientprotocol/model/Usage$$serializer;
+	public final fun childSerializers ()[Lkotlinx/serialization/KSerializer;
+	public final fun deserialize (Lkotlinx/serialization/encoding/Decoder;)Lcom/agentclientprotocol/model/Usage;
+	public synthetic fun deserialize (Lkotlinx/serialization/encoding/Decoder;)Ljava/lang/Object;
+	public final fun getDescriptor ()Lkotlinx/serialization/descriptors/SerialDescriptor;
+	public final fun serialize (Lkotlinx/serialization/encoding/Encoder;Lcom/agentclientprotocol/model/Usage;)V
+	public synthetic fun serialize (Lkotlinx/serialization/encoding/Encoder;Ljava/lang/Object;)V
+	public fun typeParametersSerializers ()[Lkotlinx/serialization/KSerializer;
+}
+
+public final class com/agentclientprotocol/model/Usage$Companion {
+	public final fun serializer ()Lkotlinx/serialization/KSerializer;
+}
+
 public final class com/agentclientprotocol/model/WaitForTerminalExitRequest : com/agentclientprotocol/model/AcpRequest, com/agentclientprotocol/model/AcpWithSessionId {
 	public static final field Companion Lcom/agentclientprotocol/model/WaitForTerminalExitRequest$Companion;
 	public synthetic fun <init> (Ljava/lang/String;Ljava/lang/String;Lkotlinx/serialization/json/JsonElement;ILkotlin/jvm/internal/DefaultConstructorMarker;)V

acp-model/src/commonMain/kotlin/com/agentclientprotocol/model/Requests.kt

@@ -687,6 +687,25 @@ public data class NewSessionResponse(
     override val _meta: JsonElement? = null
 ) : AcpCreatedSessionResponse, AcpResponse, AcpWithSessionId
 
+/**
+ * **UNSTABLE**
+ *
+ * This capability is not part of the spec yet, and may be removed or changed at any point.
+ *
+ * Token usage for a prompt turn.
+ */
+@UnstableApi
+@Serializable
+public data class Usage(
+    val inputTokens: Long,
+    val outputTokens: Long,
+    val totalTokens: Long,
+    val thoughtTokens: Long? = null,
+    val cachedReadTokens: Long? = null,
+    val cachedWriteTokens: Long? = null,
+    override val _meta: JsonElement? = null
+) : AcpWithMeta
+
 /**
  * Response from processing a user prompt.
  *
@@ -698,6 +717,8 @@ public data class PromptResponse(
     val stopReason: StopReason,
     @property:UnstableApi
     val userMessageId: MessageId? = null,
+    @property:UnstableApi
+    val usage: Usage? = null,
     override val _meta: JsonElement? = null
 ) : AcpResponse
 

acp-model/src/commonTest/kotlin/com/agentclientprotocol/model/SerializationTests.kt

@@ -3,6 +3,7 @@ package com.agentclientprotocol.model
 import com.agentclientprotocol.rpc.ACPJson
 import kotlin.test.Test
 import kotlin.test.assertEquals
+import kotlin.test.assertNull
 import kotlin.test.assertTrue
 
 class SerializationTests {
@@ -140,4 +141,73 @@ class SerializationTests {
         assertEquals(500000L, update.size)
         assertEquals(null, update.cost)
     }
+
+    @Test
+    fun `decodes PromptResponse with usage`() {
+        val payload = """
+            {
+              "stopReason": "end_turn",
+              "usage": {
+                "inputTokens": 100,
+                "outputTokens": 200,
+                "totalTokens": 300,
+                "thoughtTokens": 50,
+                "cachedReadTokens": 10,
+                "cachedWriteTokens": 5
+              }
+            }
+        """.trimIndent()
+
+        val response = ACPJson.decodeFromString(PromptResponse.serializer(), payload)
+
+        assertEquals(StopReason.END_TURN, response.stopReason)
+        val usage = response.usage
+        assertTrue(usage != null)
+        assertEquals(100L, usage.inputTokens)
+        assertEquals(200L, usage.outputTokens)
+        assertEquals(300L, usage.totalTokens)
+        assertEquals(50L, usage.thoughtTokens)
+        assertEquals(10L, usage.cachedReadTokens)
+        assertEquals(5L, usage.cachedWriteTokens)
+    }
+
+    @Test
+    fun `decodes PromptResponse with usage omitting optional fields`() {
+        val payload = """
+            {
+              "stopReason": "end_turn",
+              "usage": {
+                "inputTokens": 100,
+                "outputTokens": 200,
+                "totalTokens": 300
+              }
+            }
+        """.trimIndent()
+
+        val response = ACPJson.decodeFromString(PromptResponse.serializer(), payload)
+
+        assertEquals(StopReason.END_TURN, response.stopReason)
+        val usage = response.usage
+        assertTrue(usage != null)
+        assertEquals(100L, usage.inputTokens)
+        assertEquals(200L, usage.outputTokens)
+        assertEquals(300L, usage.totalTokens)
+        assertNull(usage.thoughtTokens)
+        assertNull(usage.cachedReadTokens)
+        assertNull(usage.cachedWriteTokens)
+    }
+
+    @Test
+    fun `decodes PromptResponse without usage`() {
+        val payload = """
+            {
+              "stopReason": "end_turn"
+            }
+        """.trimIndent()
+
+        val response = ACPJson.decodeFromString(PromptResponse.serializer(), payload)
+
+        assertEquals(StopReason.END_TURN, response.stopReason)
+        assertNull(response.usage)
+    }
 }