feat: let the current assignee reassign a pending task

Keep the same task id, move the pending inbox, and record TASK_REASSIGNED without advancing the step.

Co-authored-by: Cursor <cursoragent@cursor.com>

ordo-api/src/main/java/com/jetlumen/ordo/api/OrdoEngine.java

@@ -29,6 +29,7 @@ public interface OrdoEngine {
         return reject(taskId, actor, null);
     }
     ApprovalTask reject(String taskId, String actor, String comment);
+    ApprovalTask reassign(String taskId, String actor, String newAssignee);
     default ProcessInstance withdraw(String instanceId, String actor) {
         return withdraw(instanceId, actor, null);
     }

ordo-api/src/main/java/com/jetlumen/ordo/api/ProcessEventType.java

@@ -7,6 +7,7 @@ public enum ProcessEventType {
     TASK_APPROVED,
     TASK_REJECTED,
     TASK_SKIPPED,
+    TASK_REASSIGNED,
     INSTANCE_APPROVED,
     INSTANCE_REJECTED,
     INSTANCE_WITHDRAWN,

ordo-api/src/main/java/com/jetlumen/ordo/api/repository/ApprovalTaskRepository.java

@@ -25,12 +25,21 @@ public interface ApprovalTaskRepository {
     List<ApprovalTask> findPendingByInstanceId(String instanceId);
 
     /**
-     * Atomically completes the task only if it is still pending.
+     * Atomically completes the task only if it is still pending and still assigned to
+     * {@code completedTask.assignee()}.
      *
-     * @return true if the update was applied, false if the task had already been completed by a concurrent operation
+     * @return true if the update was applied, false if the task had already been completed or reassigned
      */
     boolean completeIfPending(ApprovalTask completedTask);
 
+    /**
+     * Atomically changes the assignee only if the task is still pending and still assigned to
+     * {@code expectedAssignee}.
+     *
+     * @return true if the update was applied
+     */
+    boolean reassignIfPending(String taskId, String expectedAssignee, String newAssignee);
+
     /** Paginated, filterable query; results are ordered newest-first (created_at desc). */
     Page<ApprovalTask> query(TaskQuery query, PageRequest pageRequest);
 }