Closing this one.

except BaseException is intentional in atomic_json_write(). The handler is not suppressing interrupts or exits; it only cleans up the temp file and then immediately re-raises. That means KeyboardInterrupt/SystemExit still propagate normally.

If we narrow this to except Exception, an interrupt during json.dump() leaves an orphaned *.tmp file behind. I verified that behavior locally by forcing json.dump() to raise KeyboardInterrupt.

atomic_yaml_write() uses the same pattern for the same reason, so this would also make the two atomic write helpers inconsistent.

Thanks for the careful look here, but I don’t think this change is correct for Hermes’ atomic-write cleanup semantics.