diff --git a/src/api/blackboard_routes.py b/src/api/blackboard_routes.py
index 1eed571..43c8ac4 100644
--- a/src/api/blackboard_routes.py
+++ b/src/api/blackboard_routes.py
@@ -91,9 +91,39 @@ async def claim_task(project_id: str, task_id: str, body: Dict[str, Any]):
 async def update_status(project_id: str, task_id: str, body: Dict[str, Any]):
     bb = _bb(project_id)
     old_task = bb.get_task(task_id)
-    if not bb.update_task_status(task_id, body["status"],
+    if not old_task:
+        raise HTTPException(404, {
+            "error": "not_found",
+            "detail": f"Task {task_id} not found in project {project_id}",
+        })
+
+    new_status = body.get("status")
+    if not new_status:
+        raise HTTPException(422, {
+            "error": "validation_failed",
+            "detail": "Missing required field: status",
+            "valid_values": {"status": sorted(VALID_STATUSES)},
+        })
+
+    # 检查转换是否合法
+    from src.blackboard.db import VALID_TRANSITIONS
+    current = old_task.status
+    allowed = VALID_TRANSITIONS.get(current, set())
+    if new_status not in allowed:
+        raise HTTPException(409, {
+            "error": "invalid_transition",
+            "detail": f"Cannot transition from {current} to {new_status}",
+            "valid_transitions": {current: sorted(allowed)},
+            "hint": f"From '{current}', valid targets are: {sorted(allowed)}",
+        })
+
+    if not bb.update_task_status(task_id, new_status,
                                   agent=body.get("agent")):
-        raise HTTPException(409, f"Invalid transition to {body['status']}")
+        raise HTTPException(409, {
+            "error": "transition_failed",
+            "detail": f"Status update failed for {task_id}",
+        })
+
     # SSE 推送
     try:
         from src.api.sse_routes import get_broker
@@ -101,13 +131,13 @@ async def update_status(project_id: str, task_id: str, body: Dict[str, Any]):
         broker.publish_sync("task_updated", {
             "project_id": project_id,
             "task_id": task_id,
-            "old_status": old_task.status if old_task else None,
-            "new_status": body["status"],
+            "old_status": current,
+            "new_status": new_status,
             "agent": body.get("agent"),
         })
     except Exception:
-        pass  # SSE 是可选的，不影响主流程
-    return {"ok": True}
+        pass
+    return {"ok": True, "old_status": current, "new_status": new_status}
 
 
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