Fix resume crash (#5)

Author: shawnlewis

programmer/agent.py

@@ -26,6 +26,7 @@ def get_last_assistant_content(history: list[Any]) -> Optional[str]:
 
 # Weave bug workaround: adding two WeaveLists can create that cause
 # downstream crashes.
+# Can be removed after https://github.com/wandb/weave/pull/2165 is merged.
 def weavelist_add(self: Union[list, WeaveList], other: list) -> Union[list, WeaveList]:
     if isinstance(self, list):
         return self + other

programmer/git.py

@@ -28,6 +28,9 @@ def create_branch(self, branch_name: str) -> None:
             # Create a new branch from the current HEAD
             self.repo.git.branch(branch_name, self.repo.head.commit.hexsha)
 
+    def checkout_existing(self, branch_name: str) -> None:
+        self.repo.git.checkout(branch_name)
+
     def commit_directly_to_branch(self, branch_name: str, message: str) -> str:
         # Ensure the branch is initialized
         self.create_branch(branch_name)