feat: add tasks models (#566)

## Motivation and Context


closes #421 
#406 

## How Has This Been Tested?
Unit tests

## Breaking Changes
NaN

## Types of changes
- [ ] Bug fix (non-breaking change which fixes an issue)
- [x] New feature (non-breaking change which adds functionality)
- [ ] Breaking change (fix or feature that would cause existing
functionality to change)
- [ ] Documentation update

## Checklist
- [x] I have read the [MCP
Documentation](https://modelcontextprotocol.io)
- [x] My code follows the repository's style guidelines
- [x] New and existing tests pass locally
- [x] I have added appropriate error handling
- [x] I have added or updated documentation as needed

Author: devcrocod

kotlin-sdk-core/api/kotlin-sdk-core.api

@@ -32,13 +32,18 @@ public sealed interface Method {
         NotificationsToolsListChanged("notifications/tools/list_changed"),
         NotificationsRootsListChanged("notifications/roots/list_changed"),
         NotificationsPromptsListChanged("notifications/prompts/list_changed"),
+        NotificationsTasksStatus("notifications/tasks/status"),
         ToolsList("tools/list"),
         ToolsCall("tools/call"),
         LoggingSetLevel("logging/setLevel"),
         SamplingCreateMessage("sampling/createMessage"),
         CompletionComplete("completion/complete"),
         RootsList("roots/list"),
         ElicitationCreate("elicitation/create"),
+        TasksGet("tasks/get"),
+        TasksResult("tasks/result"),
+        TasksList("tasks/list"),
+        TasksCancel("tasks/cancel"),
     }
 
     /**

kotlin-sdk-core/src/commonMain/kotlin/io/modelcontextprotocol/kotlin/sdk/types/methods.kt

@@ -348,3 +348,48 @@ public data class ToolListChangedNotification(override val params: BaseNotificat
     @EncodeDefault
     override val method: Method = Method.Defined.NotificationsToolsListChanged
 }
+
+// ============================================================================
+// Task Status Notification
+// ============================================================================
+
+/**
+ * An optional notification from the receiver to the requestor, informing them that a task’s status has changed.
+ * Receivers are not required to send these notifications.
+ *
+ * This notification can be sent by either side (both [ClientNotification] and [ServerNotification]).
+ *
+ * @property params The task status notification parameters containing the current task state.
+ */
+@Serializable
+public data class TaskStatusNotification(override val params: TaskStatusNotificationParams? = null) :
+    ClientNotification,
+    ServerNotification {
+    @EncodeDefault
+    override val method: Method = Method.Defined.NotificationsTasksStatus
+}
+
+/**
+ * Parameters for a notifications/tasks/status notification.
+ *
+ * @property taskId The task identifier.
+ * @property status Current task state.
+ * @property statusMessage Optional human-readable message describing the current task state.
+ * @property createdAt ISO 8601 timestamp when the task was created.
+ * @property lastUpdatedAt ISO 8601 timestamp when the task was last updated.
+ * @property ttl Actual retention duration from creation in milliseconds, null for unlimited.
+ * @property pollInterval Suggested polling interval in milliseconds.
+ * @property meta Optional metadata for this notification.
+ */
+@Serializable
+public data class TaskStatusNotificationParams(
+    override val taskId: String,
+    override val status: TaskStatus,
+    override val statusMessage: String? = null,
+    override val createdAt: String,
+    override val lastUpdatedAt: String,
+    override val ttl: Long?,
+    override val pollInterval: Long? = null,
+    @SerialName("_meta") override val meta: JsonObject? = null,
+) : NotificationParams,
+    TaskFields

kotlin-sdk-core/src/commonMain/kotlin/io/modelcontextprotocol/kotlin/sdk/types/notification.kt

@@ -6,6 +6,7 @@ import kotlinx.serialization.Serializable
 import kotlinx.serialization.json.JsonElement
 import kotlinx.serialization.json.JsonObject
 import kotlinx.serialization.json.JsonPrimitive
+import kotlinx.serialization.json.decodeFromJsonElement
 import kotlinx.serialization.json.long
 import kotlinx.serialization.json.longOrNull
 import kotlin.jvm.JvmInline
@@ -22,6 +23,17 @@ public value class RequestMeta(public val json: JsonObject) {
             }
         }
 
+    /**
+     * The related task metadata, if this request is associated with a task.
+     *
+     * @see RelatedTaskMetadata
+     * @see RELATED_TASK_META_KEY
+     */
+    public val relatedTask: RelatedTaskMetadata?
+        get() = json[RELATED_TASK_META_KEY]?.let { element ->
+            McpJson.decodeFromJsonElement(element)
+        }
+
     /**
      * Retrieves the value associated with the specified key from the JSON object.
      *

kotlin-sdk-core/src/commonMain/kotlin/io/modelcontextprotocol/kotlin/sdk/types/request.kt

@@ -159,6 +159,10 @@ private val clientRequestDeserializers: Map<String, DeserializationStrategy<Clie
         Method.Defined.ResourcesTemplatesList.value to ListResourceTemplatesRequest.serializer(),
         Method.Defined.ToolsCall.value to CallToolRequest.serializer(),
         Method.Defined.ToolsList.value to ListToolsRequest.serializer(),
+        Method.Defined.TasksGet.value to GetTaskRequest.serializer(),
+        Method.Defined.TasksResult.value to GetTaskPayloadRequest.serializer(),
+        Method.Defined.TasksList.value to ListTasksRequest.serializer(),
+        Method.Defined.TasksCancel.value to CancelTaskRequest.serializer(),
     )
 }
 
@@ -175,6 +179,10 @@ private val serverRequestDeserializers: Map<String, DeserializationStrategy<Serv
         Method.Defined.Ping.value to PingRequest.serializer(),
         Method.Defined.RootsList.value to ListRootsRequest.serializer(),
         Method.Defined.SamplingCreateMessage.value to CreateMessageRequest.serializer(),
+        Method.Defined.TasksGet.value to GetTaskRequest.serializer(),
+        Method.Defined.TasksResult.value to GetTaskPayloadRequest.serializer(),
+        Method.Defined.TasksList.value to ListTasksRequest.serializer(),
+        Method.Defined.TasksCancel.value to CancelTaskRequest.serializer(),
     )
 }
 
@@ -212,6 +220,7 @@ private val clientNotificationDeserializers: Map<String, DeserializationStrategy
         Method.Defined.NotificationsProgress.value to ProgressNotification.serializer(),
         Method.Defined.NotificationsInitialized.value to InitializedNotification.serializer(),
         Method.Defined.NotificationsRootsListChanged.value to RootsListChangedNotification.serializer(),
+        Method.Defined.NotificationsTasksStatus.value to TaskStatusNotification.serializer(),
     )
 }
 
@@ -231,6 +240,7 @@ private val serverNotificationDeserializers: Map<String, DeserializationStrategy
         Method.Defined.NotificationsResourcesListChanged.value to ResourceListChangedNotification.serializer(),
         Method.Defined.NotificationsToolsListChanged.value to ToolListChangedNotification.serializer(),
         Method.Defined.NotificationsPromptsListChanged.value to PromptListChangedNotification.serializer(),
+        Method.Defined.NotificationsTasksStatus.value to TaskStatusNotification.serializer(),
     )
 }
 
@@ -301,6 +311,9 @@ private fun selectClientResultDeserializer(element: JsonElement): Deserializatio
         "model" in jsonObject && "role" in jsonObject -> CreateMessageResult.serializer()
         "roots" in jsonObject -> ListRootsResult.serializer()
         "action" in jsonObject -> ElicitResult.serializer()
+        "task" in jsonObject -> CreateTaskResult.serializer()
+        "tasks" in jsonObject -> ListTasksResult.serializer()
+        "taskId" in jsonObject -> GetTaskResult.serializer()
         else -> null
     }
 }
@@ -309,6 +322,7 @@ private fun selectClientResultDeserializer(element: JsonElement): Deserializatio
  * Selects the appropriate deserializer for server results based on JSON content.
  * Returns null if the structure doesn't match any known server result type.
  */
+@Suppress("CyclomaticComplexMethod")
 private fun selectServerResultDeserializer(element: JsonElement): DeserializationStrategy<ServerResult>? {
     val jsonObject = element.jsonObject
     return when {
@@ -321,6 +335,9 @@ private fun selectServerResultDeserializer(element: JsonElement): Deserializatio
         "messages" in jsonObject -> GetPromptResult.serializer()
         "contents" in jsonObject -> ReadResourceResult.serializer()
         "content" in jsonObject -> CallToolResult.serializer()
+        "task" in jsonObject -> CreateTaskResult.serializer()
+        "tasks" in jsonObject -> ListTasksResult.serializer()
+        "taskId" in jsonObject -> GetTaskResult.serializer()
         else -> null
     }
 }