Fix: canvas sharing bug. (#9339)

### What problem does this PR solve?


### Type of change

- [x] Bug Fix (non-breaking change which fixes an issue)

api/db/services/canvas_service.py

@@ -121,6 +121,18 @@ class UserCanvasService(CommonService):
         agents = agents.paginate(page_number, items_per_page)
         return list(agents.dicts()), count
 
+    @classmethod
+    @DB.connection_context()
+    def accessible(cls, canvas_id, tenant_id):
+        from api.db.services.user_service import UserTenantService
+        e, c = UserCanvasService.get_by_tenant_id(canvas_id)
+        if not e:
+            return False
+
+        tids = [t.tenant_id for t in UserTenantService.query(user_id=tenant_id)]
+        if c["user_id"] != canvas_id and c["user_id"]  not in tids:
+            return False
+        return True
 
 def completion(tenant_id, agent_id, session_id=None, **kwargs):
     query = kwargs.get("query", "") or kwargs.get("question", "")