Fix bugs in agent api and update api document (#3996)

### What problem does this PR solve?

Fix bugs in agent api and update api document

### Type of change

- [x] Bug Fix (non-breaking change which fixes an issue)
- [x] New Feature (non-breaking change which adds functionality)

---------

Co-authored-by: liuhua <10215101452@stu.ecun.edu.cn>

agent/canvas.py

@@ -185,6 +185,7 @@ class Canvas(ABC):
             self.path.append(["begin"])
 
         self.path.append([])
+
         ran = -1
         waiting = []
         without_dependent_checking = []