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>

README.md

@@ -1,6 +1,6 @@
 # Ordo
 
-轻量审批流程引擎。宿主通过 `OrdoEngine` 注册流程定义、发起实例、审批/驳回/撤回，并查询任务、实例与审计历史。引擎不绑定业务表单，也不自带 REST；业务数据放在 `ProcessContext` 里。
+轻量审批流程引擎。宿主通过 `OrdoEngine` 注册流程定义、发起实例、审批/驳回/转派/撤回，并查询任务、实例与审计历史。引擎不绑定业务表单、用户体系或设计器 UI，当前也不自带 REST；业务数据放在 `ProcessContext` 里。
 
 要求 **Java 17+**。当前版本 `0.0.1-SNAPSHOT`。
 
@@ -22,11 +22,12 @@
 - 会签/或签：`ApprovalPolicy.ALL` / `ANY`（多候选人）
 - ACTION 步骤：事务提交后调用宿主 `ActionHandler`
 - 发起人撤回：`WITHDRAWN`，待办任务 `SKIPPED`
+- 任务转派：当前办理人 `reassign`，审计 `TASK_REASSIGNED`
 - 分页查询：任务 / 实例 / 流程定义
 - 审计时间线：`ProcessEvent` + `queryHistory`
 - 扩展点：`AssigneeResolver`、`RoutingCondition`、`ActionHandler`、`OrdoEventListener`
 
-开发计划：任务转派、到期升级、`CANCELLED`、定义不可变多版本、MySQL 方言。多租户与官方 REST Starter **暂不在计划中**。见 [docs/roadmap.md](docs/roadmap.md)。
+开发计划：到期升级、`CANCELLED`、定义不可变多版本、MySQL 方言、可选 REST + 目录 SPI。设计器为独立产品（不进本仓库），待 REST、目录与多版本定义之后。多租户 **暂不在计划中**。见 [docs/roadmap.md](docs/roadmap.md)。
 
 详细用法（定义 JSON、扩展点、异常、查询、ACTION/审计语义）见 **[docs/usage.md](docs/usage.md)**。对外行为变更时同步更新该文档。
 
@@ -106,13 +107,14 @@ ordo:
 | Bean | 默认 |
 |---|---|
 | `AssigneeResolver` | 候选人即办理人 |
-| `RoutingCondition` | 始终匹配 |
+| `RoutingCondition` | 始终匹配（全局单例；宿主可按 key 分发） |
 | `ActionHandler` | 空操作 |
 | `OrdoEventListener` | 可注册多个，提交后按顺序调用 |
 
 ## 运行时约定
 
-**办理人** 必须等于任务 `assignee`，否则 `UnauthorizedTaskOperationException`。  
+**办理人** 必须等于任务 `assignee`，否则 `UnauthorizedTaskOperationException`（`approve` / `reject` / `reassign`）。  
+**转派** 只改 PENDING 任务的 `assignee`，不推进步骤。  
 **撤回** 仅发起人可操作，且实例须为 `RUNNING`。
 
 实例状态：`RUNNING` / `APPROVED` / `REJECTED` / `WITHDRAWN`。  
@@ -120,7 +122,7 @@ ordo:
 
 **ACTION** 在审批事务提交之后执行。失败只记 `FAILED`、打日志、发 `ACTION_FAILED`，**不回滚已生效审批、不阻塞后续步骤**。可重试策略留给宿主（listener 或 `queryActionExecutions`）。
 
-**历史** `queryHistory(instanceId, page)` 按时间升序。事件类型包括实例起止、任务创建/审批/跳过、ACTION 成败。  
+**历史** `queryHistory(instanceId, page)` 按时间升序。事件类型包括实例起止、任务创建/审批/跳过/转派、ACTION 成败。  
 `OrdoEventListener.onEvent` 在提交后派发；单个 listener 抛错不影响流程和其他 listener。
 
 ## 查询

docs/roadmap.md

@@ -13,15 +13,12 @@
 - 发起人撤回 `WITHDRAWN`
 - 分页查询：任务 / 实例 / 定义
 - 审计 `ProcessEvent` / `queryHistory`；`OrdoEventListener`
+- 任务转派 `reassign` / `TASK_REASSIGNED`
 
 ## 开发计划（确定要做）
 
 下列能力已纳入计划，尚未实现。实现顺序可按依赖调整，但范围本身不从计划中拿掉。
 
-### 任务转派
-
-任务创建后当前 `assignee` 不可变。计划提供委托/转派（delegate/reassign），把待办转给他人办理，并写入审计。
-
 ### 到期升级
 
 目前无到期时间与定时器。计划支持 SLA/超时：到期后升级（改办理人、通知或进入指定步骤），即「到期升级」。
@@ -38,13 +35,27 @@
 
 当前 JDBC DDL/冲突处理面向 PostgreSQL。计划增加 MySQL 方言（及对应测试），通过 dialect 层扩展，而不是只支持一种库。
 
+### 可选 REST + 目录 SPI
+
+引擎入口仍是 `OrdoEngine`。计划提供**可选、极薄**的 REST 适配（例如独立 starter），带 OpenAPI，覆盖定义读写/解析校验、实例与任务查询，不包含鉴权、RBAC、业务表单。
+
+配套 **目录 SPI**：宿主登记可用的 `conditionKey` / `actionKey` / 候选人（或角色）项，供 REST 与外部设计器下拉，而不是在 JSON 里写引擎无法执行的表达式。
+
+`RoutingCondition` / `ActionHandler` / `AssigneeResolver` 保持全局单例；流程隔离由宿主用 key 约定（建议前缀）+ 门面分发，引擎不按流程定义拆 bean。
+
+### 独立设计器（不进本仓库）
+
+流程设计器是**单独产品**，消费上述 REST 与目录，不做成 ordo 模块。画布对齐引擎图（审批步、ACTION 步、边上的 `when`/`priority`，结束为 `to: null`），不引入 BPMN 网关/并行等引擎没有的语义。节点坐标等 layout 由设计器自存，不进入 `ProcessDefinition`。
+
+启动时机：REST 契约、目录 SPI、定义不可变多版本落地之后。当前 `replace` + 无版本锁定不适合作为设计器保存/发布模型。
+
 ## 暂不在计划中
 
 - **多租户**（数据模型无 tenant 隔离）
-- **官方 REST Starter**（不提供 `ordo-spring-boot-starter-web`；REST 由宿主自建）
+- **设计器 UI**（不进 ordo；见上节独立产品）
 
 ## 后续新特性
 
-上表「确定要做」之外，仍可能立项其他能力（例如表单/UI schema、子流程、并行 fork-join）。**多租户与官方 REST 在另有明确决定前不进入计划。**
+上表「确定要做」之外，仍可能立项其他能力（例如表单/UI schema、子流程、并行 fork-join）。**多租户在另有明确决定前不进入计划。**
 
 新特性立项时写入「开发计划」对应小节；完成后移到「已完成」，并更新 [usage.md](usage.md)。

docs/usage.md

@@ -10,9 +10,9 @@ Ordo 是嵌入宿主进程的审批引擎，入口是 `OrdoEngine`。
 
 做：流程定义、实例推进、待办任务、条件路由、ACTION 副作用、审计事件、分页查询。
 
-产品边界（不做，且暂不在开发计划）：业务表单、用户体系、官方 REST、多租户。业务字段放在 `ProcessContext`（不可变 `Map<String, Object>`）。
+产品边界：不做业务表单、用户体系、多租户；不内置设计器 UI。业务字段放在 `ProcessContext`（不可变 `Map<String, Object>`）。当前也**没有** REST；HTTP 仍由宿主自建。计划中的可选 REST 与独立设计器见 [roadmap.md](roadmap.md)。
 
-开发计划（尚未提供，见 [roadmap.md](roadmap.md)）：任务转派、到期升级、`CANCELLED`、定义不可变多版本、MySQL 方言。
+开发计划（尚未提供，见 [roadmap.md](roadmap.md)）：到期升级、`CANCELLED`、定义不可变多版本、MySQL 方言、可选 REST + 目录 SPI。
 
 ## 2. 模块与接入
 
@@ -189,7 +189,8 @@ ProcessInstance instance = ordo.start("leave-request", "alice",
         new ProcessContext(Map.of("requestId", "LEAVE-001", "days", 2)));
 
 List<ApprovalTask> pending = ordo.findPendingTasksByInstanceId(instance.id());
-ordo.approve(pending.get(0).id(), "maria", "ok");
+ordo.reassign(pending.get(0).id(), "maria", "diana");
+ordo.approve(pending.get(0).id(), "diana", "ok");
 
 ordo.reject(taskId, "maria", "额度不足");
 ordo.withdraw(instance.id(), "alice", "计划有变");
@@ -199,11 +200,12 @@ ordo.withdraw(instance.id(), "alice", "计划有变");
 
 ### 4.2 权限
 
-- `approve` / `reject`：`actor` 必须等于该任务当前 `assignee`，否则 `UnauthorizedTaskOperationException`。
+- `approve` / `reject` / `reassign`：`actor` 必须等于该任务当前 `assignee`，否则 `UnauthorizedTaskOperationException`。
+- `reassign`：仅 `PENDING` 任务；同一任务 id，办理人改为 `newAssignee`，不推进步骤。`newAssignee` 不可空白、不可等于当前 `assignee`，且同一步不能已有该人的 `PENDING` 任务，否则 `IllegalArgumentException`。不经过 `AssigneeResolver`。
 - 任务非 `PENDING`：`TaskAlreadyCompletedException`。
 - `withdraw`：仅 `initiator`，否则 `UnauthorizedInstanceOperationException`；实例非 `RUNNING`：`InstanceAlreadyCompletedException`。
 
-没有转派、没有管理员代批、没有系统取消。
+没有管理员代批、没有系统取消。
 
 ### 4.3 状态
 
@@ -237,7 +239,9 @@ ordo.withdraw(instance.id(), "alice", "计划有变");
 
 无条件边通常作为默认分支，`priority` 应大于带 `when` 的边。
 
-`RoutingCondition` 只看到 `ProcessContext`，看不到任务意见。上下文在 `start` 时写入，运行中引擎**不会**改 context。
+`RoutingCondition` 只看到 `ProcessContext`，看不到任务意见，也**没有**流程定义 id。上下文在 `start` 时写入，运行中引擎**不会**改 context。
+
+引擎只注入**一个** `RoutingCondition`（与 `ActionHandler` 相同）。Spring 下多个该类型 Bean 会冲突。宿主用一个门面按 `conditionKey` 分发到多套规则；不同流程靠 key 约定隔离（例如 `leave.days-gt-3`），不要指望引擎按定义拆 bean。
 
 ## 7. ACTION 步骤
 
@@ -271,10 +275,10 @@ public class MailActions implements ActionHandler {
 `ProcessEventType`：
 
 - `INSTANCE_STARTED` / `INSTANCE_APPROVED` / `INSTANCE_REJECTED` / `INSTANCE_WITHDRAWN`
-- `TASK_CREATED` / `TASK_APPROVED` / `TASK_REJECTED` / `TASK_SKIPPED`
+- `TASK_CREATED` / `TASK_APPROVED` / `TASK_REJECTED` / `TASK_SKIPPED` / `TASK_REASSIGNED`
 - `ACTION_SUCCEEDED` / `ACTION_FAILED`
 
-字段：`id`、`instanceId`、可选 `taskId`/`stepId`/`actor`/`detail`、`occurredAt`。系统完成类事件 `actor` 可为空。
+字段：`id`、`instanceId`、可选 `taskId`/`stepId`/`actor`/`detail`、`occurredAt`。系统完成类事件 `actor` 可为空。`TASK_REASSIGNED` 的 `actor` 为转出人，`detail` 为转入人。
 
 `OrdoEventListener.onEvent(ProcessEvent)` 在**事务提交之后**按事件顺序调用（含本轮 ACTION 结果）。单个 listener 抛错只打日志，不影响流程和其他 listener。
 
@@ -307,6 +311,7 @@ ACTION 成功事件发生在提交之后，因此排在同轮事务内写入的
 | `register` / `replace` | 登记 / 整图替换定义 |
 | `start` | 发起；可选 `ProcessContext` |
 | `approve` / `reject` | 办理当前 PENDING 任务 |
+| `reassign` | 当前办理人把 PENDING 任务转给他人 |
 | `withdraw` | 发起人撤回 |
 | `find*` | 按 id / 待办索引读取 |
 | `queryTasks` / `queryInstances` / `queryDefinitions` | 分页列表 |
@@ -325,7 +330,7 @@ ACTION 成功事件发生在提交之后，因此排在同轮事务内写入的
 | `InstanceAlreadyCompletedException` | 对非 RUNNING 实例完成/撤回 |
 | `TaskNotFoundException` | 任务 id 不存在 |
 | `TaskAlreadyCompletedException` | 重复办理或已被 SKIPPED |
-| `UnauthorizedTaskOperationException` | actor ≠ assignee |
+| `UnauthorizedTaskOperationException` | actor ≠ 当前 assignee（approve / reject / reassign） |
 | `UnauthorizedInstanceOperationException` | 非发起人撤回 |
 | `NoRouteFoundException` | 当前步没有匹配转移 |
 
@@ -339,6 +344,6 @@ Flyway 脚本在 `ordo-storage-jdbc` 的 `db/migration`（V1–V5）。表包括
 
 ## 13. 未提供能力
 
-开发计划中（见 [roadmap.md](roadmap.md)）：转派、到期升级、`CANCELLED`、定义不可变多版本、MySQL 方言。
+开发计划中（见 [roadmap.md](roadmap.md)）：到期升级、`CANCELLED`、定义不可变多版本、MySQL 方言、可选 REST + 目录 SPI。独立设计器不进本仓库，等 REST、目录与多版本定义之后再做。
 
-暂不在计划中：多租户、官方 REST Starter。REST 由宿主自建。
+暂不在计划中：多租户、设计器 UI。当前 REST 由宿主自建。

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);
 }

ordo-core/src/main/java/com/jetlumen/ordo/core/DefaultOrdoEngine.java

@@ -174,6 +174,36 @@ public final class DefaultOrdoEngine implements OrdoEngine {
         return completed;
     }
 
+    @Override
+    public synchronized ApprovalTask reassign(String taskId, String actor, String newAssignee) {
+        requireText(newAssignee, "new assignee");
+        List<ProcessEvent> events = new ArrayList<>();
+        ApprovalTask reassigned = transactionExecutor.execute(() -> {
+            ApprovalTask task = requirePendingTaskForActor(taskId, actor);
+            if (task.assignee().equals(newAssignee)) {
+                throw new IllegalArgumentException("new assignee must differ from current assignee");
+            }
+            boolean duplicatePending = taskRepository.findByInstanceIdAndStepId(task.instanceId(), task.stepId()).stream()
+                    .anyMatch(other -> !other.id().equals(task.id())
+                            && other.status() == TaskStatus.PENDING
+                            && other.assignee().equals(newAssignee));
+            if (duplicatePending) {
+                throw new IllegalArgumentException("new assignee already has a pending task on this step");
+            }
+            if (!taskRepository.reassignIfPending(task.id(), task.assignee(), newAssignee)) {
+                throw new TaskAlreadyCompletedException(task.id());
+            }
+            Instant now = clock.instant();
+            ApprovalTask updated = new ApprovalTask(task.id(), task.instanceId(), task.stepId(), task.name(),
+                    newAssignee, task.status(), task.createdAt(), task.completedAt(), task.action());
+            record(events, task.instanceId(), task.id(), task.stepId(), ProcessEventType.TASK_REASSIGNED, actor,
+                    newAssignee, now);
+            return updated;
+        });
+        dispatch(events);
+        return reassigned;
+    }
+
     @Override
     public synchronized ProcessInstance withdraw(String instanceId, String actor, String comment) {
         requireText(instanceId, "instance id");

ordo-core/src/main/java/com/jetlumen/ordo/core/InMemoryOrdoEngine.java

@@ -100,6 +100,11 @@ public final class InMemoryOrdoEngine implements OrdoEngine {
         return delegate.reject(taskId, actor, comment);
     }
 
+    @Override
+    public ApprovalTask reassign(String taskId, String actor, String newAssignee) {
+        return delegate.reassign(taskId, actor, newAssignee);
+    }
+
     @Override
     public ProcessInstance withdraw(String instanceId, String actor, String comment) {
         return delegate.withdraw(instanceId, actor, comment);

ordo-core/src/main/java/com/jetlumen/ordo/core/repository/InMemoryApprovalTaskRepository.java

@@ -76,13 +76,26 @@ public final class InMemoryApprovalTaskRepository implements ApprovalTaskReposit
     @Override
     public synchronized boolean completeIfPending(ApprovalTask completedTask) {
         ApprovalTask current = tasks.get(completedTask.id());
-        if (current == null || current.status() != TaskStatus.PENDING) {
+        if (current == null || current.status() != TaskStatus.PENDING
+                || !current.assignee().equals(completedTask.assignee())) {
             return false;
         }
         tasks.put(completedTask.id(), completedTask);
         return true;
     }
 
+    @Override
+    public synchronized boolean reassignIfPending(String taskId, String expectedAssignee, String newAssignee) {
+        ApprovalTask current = tasks.get(taskId);
+        if (current == null || current.status() != TaskStatus.PENDING
+                || !current.assignee().equals(expectedAssignee)) {
+            return false;
+        }
+        tasks.put(taskId, new ApprovalTask(current.id(), current.instanceId(), current.stepId(), current.name(),
+                newAssignee, current.status(), current.createdAt(), current.completedAt(), current.action()));
+        return true;
+    }
+
     @Override
     public synchronized Page<ApprovalTask> query(TaskQuery query, PageRequest pageRequest) {
         List<ApprovalTask> matched = tasks.values().stream().filter(task -> matches(task, query)).toList();

ordo-core/src/test/java/com/jetlumen/ordo/core/InMemoryOrdoEngineTest.java

@@ -93,6 +93,64 @@ class InMemoryOrdoEngineTest {
         assertThrows(TaskAlreadyCompletedException.class, () -> engine.approve(task.id(), "maria"));
     }
 
+    @Test
+    void reassignsAPendingTaskToAnotherAssignee() {
+        var instance = engine.start("leave", "alice");
+        ApprovalTask task = engine.findPendingTasksByInstanceId(instance.id()).get(0);
+
+        ApprovalTask reassigned = engine.reassign(task.id(), "maria", "diana");
+
+        assertEquals(task.id(), reassigned.id());
+        assertEquals("diana", reassigned.assignee());
+        assertEquals(TaskStatus.PENDING, reassigned.status());
+        assertTrue(engine.findPendingTasksByAssignee("maria").isEmpty());
+        assertEquals(List.of(reassigned), engine.findPendingTasksByAssignee("diana"));
+        ProcessEvent event = engine.queryHistory(instance.id(), new PageRequest(0, 20)).content().stream()
+                .filter(e -> e.type() == ProcessEventType.TASK_REASSIGNED)
+                .findFirst()
+                .orElseThrow();
+        assertEquals("maria", event.actor());
+        assertEquals("diana", event.detail());
+        engine.approve(task.id(), "diana");
+        assertEquals("hr", engine.findPendingTasksByInstanceId(instance.id()).get(0).stepId());
+    }
+
+    @Test
+    void reassignIsRejectedForUnauthorizedCompletedSelfAndDuplicateAssignees() {
+        var instance = engine.start("leave", "alice");
+        ApprovalTask task = engine.findPendingTasksByInstanceId(instance.id()).get(0);
+
+        assertThrows(UnauthorizedTaskOperationException.class, () -> engine.reassign(task.id(), "mallory", "diana"));
+        assertThrows(IllegalArgumentException.class, () -> engine.reassign(task.id(), "maria", "maria"));
+        assertThrows(IllegalArgumentException.class, () -> engine.reassign(task.id(), "maria", " "));
+
+        engine.approve(task.id(), "maria");
+        assertThrows(TaskAlreadyCompletedException.class, () -> engine.reassign(task.id(), "maria", "diana"));
+    }
+
+    @Test
+    void reassignDoesNotAdvanceAnAllPolicyStepAndRejectsDuplicatePendingAssignee() {
+        InMemoryOrdoEngine allEngine = new InMemoryOrdoEngine();
+        allEngine.register(ProcessDefinition.linear("leave-all-reassign", "Leave request", List.of(
+                new ApprovalStep("manager", "Manager approval", List.of("maria", "mike"), ApprovalPolicy.ALL)
+        )));
+        var instance = allEngine.start("leave-all-reassign", "alice");
+        List<ApprovalTask> managerTasks = allEngine.findTasks(instance.id());
+        ApprovalTask mariaTask = managerTasks.stream().filter(t -> t.assignee().equals("maria")).findFirst().orElseThrow();
+        ApprovalTask mikeTask = managerTasks.stream().filter(t -> t.assignee().equals("mike")).findFirst().orElseThrow();
+
+        assertThrows(IllegalArgumentException.class, () -> allEngine.reassign(mariaTask.id(), "maria", "mike"));
+
+        ApprovalTask reassigned = allEngine.reassign(mariaTask.id(), "maria", "diana");
+        assertEquals(TaskStatus.PENDING, allEngine.findTask(mikeTask.id()).orElseThrow().status());
+        assertEquals(ProcessStatus.RUNNING, allEngine.findInstance(instance.id()).orElseThrow().status());
+        assertEquals(2, allEngine.findPendingTasksByInstanceId(instance.id()).size());
+        allEngine.approve(reassigned.id(), "diana");
+        assertEquals(ProcessStatus.RUNNING, allEngine.findInstance(instance.id()).orElseThrow().status());
+        allEngine.approve(mikeTask.id(), "mike");
+        assertEquals(ProcessStatus.APPROVED, allEngine.findInstance(instance.id()).orElseThrow().status());
+    }
+
     @Test
     void exposesSpecificExceptionsForMissingAndDuplicateResources() {
         assertThrows(DefinitionNotFoundException.class, () -> engine.start("missing", "alice"));
@@ -185,6 +243,7 @@ class InMemoryOrdoEngineTest {
         ApprovalTask task = engine.findTasks(instance.id()).get(0);
         assertThrows(IllegalArgumentException.class, () -> engine.approve(task.id(), " "));
         assertThrows(IllegalArgumentException.class, () -> engine.reject(task.id(), " "));
+        assertThrows(IllegalArgumentException.class, () -> engine.reassign(task.id(), " ", "diana"));
     }
 
     @Test

ordo-core/src/test/java/com/jetlumen/ordo/core/repository/InMemoryApprovalTaskRepositoryTest.java

@@ -75,6 +75,24 @@ class InMemoryApprovalTaskRepositoryTest {
         assertEquals(List.of(leaveTask), byDefinition.content());
     }
 
+    @Test
+    void reassignIfPendingUpdatesOnlyAMatchingPendingTask() {
+        InMemoryApprovalTaskRepository repository = new InMemoryApprovalTaskRepository();
+        ApprovalTask pending = task("task-1", "inst-1", "maria", TaskStatus.PENDING, CREATED_AT);
+        repository.save(pending);
+
+        assertTrue(repository.reassignIfPending("task-1", "maria", "diana"));
+        assertEquals("diana", repository.findById("task-1").orElseThrow().assignee());
+        assertFalse(repository.reassignIfPending("task-1", "maria", "henry"));
+        assertEquals("diana", repository.findById("task-1").orElseThrow().assignee());
+
+        ApprovalTask completed = new ApprovalTask(pending.id(), pending.instanceId(), pending.stepId(), pending.name(),
+                "diana", TaskStatus.APPROVED, pending.createdAt(), CREATED_AT.plusSeconds(1), null);
+        assertTrue(repository.completeIfPending(completed));
+        assertFalse(repository.reassignIfPending("task-1", "diana", "henry"));
+        assertFalse(repository.reassignIfPending("missing", "maria", "diana"));
+    }
+
     private static ApprovalTask task(String id, String instanceId, String assignee, TaskStatus status, Instant createdAt) {
         return new ApprovalTask(id, instanceId, "step", "Step", assignee, status, createdAt, null, null);
     }

ordo-storage-jdbc/src/main/java/com/jetlumen/ordo/storage/jdbc/JdbcApprovalTaskRepository.java

@@ -27,7 +27,9 @@ public final class JdbcApprovalTaskRepository implements ApprovalTaskRepository
                     + " VALUES (?, ?, ?, ?, ?, ?, ?)";
     private static final String COMPLETE_IF_PENDING =
             "UPDATE ordo_approval_task SET status = ?, completed_at = ?, action_actor = ?, action_comment = ?, action_at = ?"
-                    + " WHERE id = ? AND status = 'PENDING'";
+                    + " WHERE id = ? AND status = 'PENDING' AND assignee = ?";
+    private static final String REASSIGN_IF_PENDING =
+            "UPDATE ordo_approval_task SET assignee = ? WHERE id = ? AND status = 'PENDING' AND assignee = ?";
     private static final String SELECT_TASK =
             "SELECT " + TASK_COLUMNS + " FROM ordo_approval_task WHERE id = ?";
     private static final String SELECT_BY_INSTANCE =
@@ -119,6 +121,24 @@ public final class JdbcApprovalTaskRepository implements ApprovalTaskRepository
         }
     }
 
+    @Override
+    public boolean reassignIfPending(String taskId, String expectedAssignee, String newAssignee) {
+        Objects.requireNonNull(taskId, "taskId must not be null");
+        Objects.requireNonNull(expectedAssignee, "expectedAssignee must not be null");
+        Objects.requireNonNull(newAssignee, "newAssignee must not be null");
+        Connection connection = connectionProvider.getConnection();
+        try (PreparedStatement update = connection.prepareStatement(REASSIGN_IF_PENDING)) {
+            update.setString(1, newAssignee);
+            update.setString(2, taskId);
+            update.setString(3, expectedAssignee);
+            return update.executeUpdate() == 1;
+        } catch (SQLException e) {
+            throw new JdbcStorageException("failed to reassign task: " + taskId, e);
+        } finally {
+            connectionProvider.close(connection);
+        }
+    }
+
     @Override
     public Page<ApprovalTask> query(TaskQuery query, PageRequest pageRequest) {
         Objects.requireNonNull(query, "query must not be null");

ordo-storage-jdbc/src/main/java/com/jetlumen/ordo/storage/jdbc/mapper/ApprovalTaskMapper.java

@@ -40,6 +40,7 @@ public final class ApprovalTaskMapper {
             statement.setTimestamp(5, Timestamp.from(action.operatedAt()));
         }
         statement.setString(6, completedTask.id());
+        statement.setString(7, completedTask.assignee());
     }
 
     public static ApprovalTask read(ResultSet resultSet) throws SQLException {

ordo-storage-jdbc/src/test/java/com/jetlumen/ordo/storage/jdbc/JdbcApprovalTaskRepositoryTest.java

@@ -154,6 +154,70 @@ class JdbcApprovalTaskRepositoryTest {
         assertTrue(Set.of("first", "second").contains(stored.action().comment()));
     }
 
+    @Test
+    void reassignIfPendingUpdatesAssigneeAndFailsWhenNotPending() {
+        ApprovalTask pending = pendingTask("task-1", "inst-1", "manager", "maria", CREATED_AT);
+        repository.save(pending);
+
+        assertTrue(repository.reassignIfPending("task-1", "maria", "diana"));
+        assertEquals("diana", repository.findById("task-1").orElseThrow().assignee());
+        assertEquals(List.of(repository.findById("task-1").orElseThrow()), repository.findPendingByAssignee("diana"));
+        assertTrue(repository.findPendingByAssignee("maria").isEmpty());
+        assertFalse(repository.reassignIfPending("task-1", "maria", "henry"));
+
+        assertTrue(repository.completeIfPending(completedTask(repository.findById("task-1").orElseThrow(), "ok")));
+        assertFalse(repository.reassignIfPending("task-1", "diana", "henry"));
+    }
+
+    @Test
+    void onlyOneOfConcurrentReassignAndCompletionWins() throws Exception {
+        ApprovalTask pending = pendingTask("task-1", "inst-1", "manager", "maria", CREATED_AT);
+        repository.save(pending);
+
+        CountDownLatch start = new CountDownLatch(1);
+        CountDownLatch done = new CountDownLatch(2);
+        AtomicInteger completeWins = new AtomicInteger();
+        AtomicInteger reassignWins = new AtomicInteger();
+        Thread completer = new Thread(() -> {
+            try {
+                start.await();
+                if (repository.completeIfPending(completedTask(pending, "ok"))) {
+                    completeWins.incrementAndGet();
+                }
+            } catch (InterruptedException e) {
+                Thread.currentThread().interrupt();
+            } finally {
+                done.countDown();
+            }
+        });
+        Thread reassigner = new Thread(() -> {
+            try {
+                start.await();
+                if (repository.reassignIfPending("task-1", "maria", "diana")) {
+                    reassignWins.incrementAndGet();
+                }
+            } catch (InterruptedException e) {
+                Thread.currentThread().interrupt();
+            } finally {
+                done.countDown();
+            }
+        });
+        completer.start();
+        reassigner.start();
+        start.countDown();
+
+        assertTrue(done.await(10, TimeUnit.SECONDS));
+        assertEquals(1, completeWins.get() + reassignWins.get());
+        ApprovalTask stored = repository.findById("task-1").orElseThrow();
+        if (completeWins.get() == 1) {
+            assertEquals(TaskStatus.APPROVED, stored.status());
+            assertEquals("maria", stored.assignee());
+        } else {
+            assertEquals(TaskStatus.PENDING, stored.status());
+            assertEquals("diana", stored.assignee());
+        }
+    }
+
     private void attempt(CountDownLatch start, CountDownLatch done, AtomicInteger wins, ApprovalTask completed) {
         try {
             start.await();

ordo-storage-jdbc/src/test/java/com/jetlumen/ordo/storage/jdbc/JdbcOrdoEngineIntegrationTest.java

@@ -97,6 +97,27 @@ class JdbcOrdoEngineIntegrationTest {
         assertEquals("hr", engine.findPendingTasksByInstanceId(instance.id()).get(0).stepId());
     }
 
+    @Test
+    void reassignsAPendingTaskAndRecordsHistory() {
+        ProcessInstance instance = engine.start("leave", "alice");
+        ApprovalTask task = engine.findPendingTasksByInstanceId(instance.id()).get(0);
+
+        ApprovalTask reassigned = engine.reassign(task.id(), "maria", "diana");
+
+        assertEquals("diana", reassigned.assignee());
+        assertEquals(TaskStatus.PENDING, reassigned.status());
+        assertTrue(engine.findPendingTasksByAssignee("maria").isEmpty());
+        assertEquals("diana", engine.findPendingTasksByAssignee("diana").get(0).assignee());
+        List<ProcessEvent> history = engine.queryHistory(instance.id(), new PageRequest(0, 20)).content();
+        ProcessEvent reassignedEvent = history.stream()
+                .filter(event -> event.type() == ProcessEventType.TASK_REASSIGNED)
+                .findFirst()
+                .orElseThrow();
+        assertEquals("maria", reassignedEvent.actor());
+        assertEquals("diana", reassignedEvent.detail());
+        assertEquals(task.id(), reassignedEvent.taskId());
+    }
+
     @Test
     void rollsBackTheWholeApprovalWhenTheNextStepCannotBeCreated() {
         OrdoEngine failingEngine = newEngine((candidate, step, context) -> {