feat(task): simplify Task message and CreateTasksRequest

Remove mission_id from CreateTasksRequest, replace last_updated/error
fields with heartbeat_at in Task message, renumber fields accordingly.

Author: Relixik

proto/agentic_mesh_protocol/task_manager/v1/task_manager_dto.proto

@@ -26,22 +26,8 @@ import "buf/validate/validate.proto";
 // - mission_id: Mission the tasks belong to.
 // - tasks: List of task definitions to create.
 message CreateTasksRequest {
-  // mission_id is the mission the tasks belong to.
-  string mission_id = 1 [
-    (buf.validate.field).required = true,
-    (buf.validate.field).cel = {
-      id: "mission_id_prefix"
-      expression: "this.startsWith('missions:')"
-      message: "mission_id must start with 'missions:'"
-    },
-    (buf.validate.field).cel = {
-      id: "mission_id_length"
-      expression: "this.size() >= 10"
-      message: "mission_id must be at least 1 characters long"
-    }
-  ];
   // tasks is the list of task definitions to create.
-  repeated Task tasks = 2 [
+  repeated Task tasks = 1 [
     (buf.validate.field).repeated.min_items = 1
   ];
 }

proto/agentic_mesh_protocol/task_manager/v1/task_manager_message.proto

@@ -48,8 +48,7 @@ message TaskError {
 // - status: Current lifecycle status.
 // - action: Latest signal action type.
 // - created_at: When the task was created.
-// - last_updated: When the task was last updated.
-// - error: Optional error details.
+// - heartbeat_at: When the task sent its last heartbeat.
 // - payload: Optional structured payload.
 message Task {
   // task_id is the unique identifier of the task.
@@ -116,10 +115,8 @@ message Task {
   optional string action = 6;
   // created_at is when the task was created.
   google.protobuf.Timestamp created_at = 7;
-  // last_updated is when the task was last updated.
-  optional google.protobuf.Timestamp last_updated = 8;
-  // error is the optional error details.
-  optional TaskError error = 9;
+  // heartbeat_at is when the task last sent a heartbeat.
+  optional google.protobuf.Timestamp heartbeat_at = 8;
   // payload is an optional structured payload.
-  optional google.protobuf.Struct payload = 10;
+  optional google.protobuf.Struct payload = 9;
 }