get_latest_data_deepcopy_snapshot deep-copies layers outside the data lock; a writer mutating a nested object in place races it and raises "dictionary changed size during iteration" (500 on /api/health, /api/live-data). Two changes: (1) _merge_sigint_snapshot now shallow-copies each entry so latest_data["sigint"] no longer aliases the SIGINT bridge dicts or the meshtastic_map_nodes layer (the concrete offender); (2) the snapshot retries a few times as defense-in-depth for any other in-place mutator. Plus regression tests.
TheYellowBeanieGuy