feat: let initiators withdraw running process instances

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

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

@@ -24,6 +24,10 @@ public interface OrdoEngine {
         return reject(taskId, actor, null);
     }
     ApprovalTask reject(String taskId, String actor, String comment);
+    default ProcessInstance withdraw(String instanceId, String actor) {
+        return withdraw(instanceId, actor, null);
+    }
+    ProcessInstance withdraw(String instanceId, String actor, String comment);
     Optional<ProcessInstance> findInstance(String instanceId);
     Optional<ApprovalTask> findTask(String taskId);
     List<ApprovalTask> findTasks(String instanceId);

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

@@ -1,5 +1,5 @@
 package com.jetlumen.ordo.api;
 
 public enum ProcessStatus {
-    RUNNING, APPROVED, REJECTED
+    RUNNING, APPROVED, REJECTED, WITHDRAWN
 }

ordo-api/src/main/java/com/jetlumen/ordo/api/exception/InstanceAlreadyCompletedException.java

@@ -0,0 +1,7 @@
+package com.jetlumen.ordo.api.exception;
+
+public final class InstanceAlreadyCompletedException extends OrdoException {
+    public InstanceAlreadyCompletedException(String instanceId) {
+        super("instance is already completed: " + instanceId);
+    }
+}

ordo-api/src/main/java/com/jetlumen/ordo/api/exception/InstanceNotFoundException.java

@@ -0,0 +1,7 @@
+package com.jetlumen.ordo.api.exception;
+
+public final class InstanceNotFoundException extends OrdoException {
+    public InstanceNotFoundException(String instanceId) {
+        super("instance not found: " + instanceId);
+    }
+}

ordo-api/src/main/java/com/jetlumen/ordo/api/exception/UnauthorizedInstanceOperationException.java

@@ -0,0 +1,7 @@
+package com.jetlumen.ordo.api.exception;
+
+public final class UnauthorizedInstanceOperationException extends OrdoException {
+    public UnauthorizedInstanceOperationException(String instanceId, String actor) {
+        super("actor '" + actor + "' is not the initiator for instance: " + instanceId);
+    }
+}

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

@@ -15,4 +15,11 @@ public interface ProcessInstanceRepository {
     Optional<ProcessInstance> findById(String instanceId);
 
     boolean existsRunning(String definitionId);
+
+    /**
+     * Completes the instance only if it is still running.
+     *
+     * @return true if the update was applied, false if the instance was missing or already terminal
+     */
+    boolean completeIfRunning(ProcessInstance completed);
 }