infrastructure-callback-safety-typeerror-nonetype-object-is-not-callable-appears--b37d7220

THEN In langgraph/pregel/runner.py, add a defensive check for None on the callback returned by self.callback() before invoking it. Wrap the call with 'if cb is not None: cb(task, _exception(fut))' to prevent the exception when the callback has been cleaned up due to task cancellation.

def on_done(self, task, fut):
    try:
        cb = self.callback()
        if cb is not None:
            cb(task, _exception(fut))
    finally:
        # ... existing cleanup ...