fix(record): avoid ZeroDivisionError in HttpRecorder final-report fallback

[WatchTree-19]

summary

HttpRecorder.record_final_report builds a final_report event and sends it with self._send_event([report_event]), but it does not append that event to self._events. For a run that recorded no sample events, self._events stays empty.

When the POST fails, _send_event runs:

self.failed_requests += len(events)
...
if self.failed_requests / len(self._events) > fail_threshold:   # len(self._events) == 0

so it raises ZeroDivisionError. record_final_report only catches RuntimeError, so the ZeroDivisionError propagates and crashes the run instead of falling back to the LocalRecorder.

fix

total_events = len(self._events) or len(events)
if self.failed_requests / total_events > fail_threshold:

_send_event is only ever called with a non-empty batch, so this keeps the ratio well-defined. In the empty-events case the threshold is now exceeded and a RuntimeError is raised, which record_final_report catches and uses to fall back to the LocalRecorder (the intended behavior). The normal (non-empty) path is unchanged.

test

adds test_http_recorder_final_report_no_events_falls_back_without_zerodivision to evals/record_test.py: with requests.post patched to fail and no recorded events, record_final_report must not raise and the report must be written by the fallback LocalRecorder. the test fails with ZeroDivisionError without the fix and passes with it.