- send_import_zero_length_payload_delivers_empty: payload_len=0 delivers empty msg
- actors_from_separate_engines_coexist: two engines on same runtime work independently
- rapid_spawn_send_stop_50_rounds: 50 sequential spawn-send-stop cycles all deliver
- start_function_that_succeeds_allows_normal_operation: start initializes global, handle uses it
All 135 tests pass. No new bugs found.
Authored by Claude, lovingly guided by Zachery Aaron Shores-Chmielewski
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