Cover context+callback propagation and teardown-clears, a source guard that both RPC threads stay wrapped, the check_execute_code_guard decision matrix (isolated backend, headless-local, cron-deny, gateway approve/deny/timeout/missing-notify, smart mode, session-yolo), the env-scrub allowlist/secret rules, and a behavioral test that execute_code() blocks before spawning on denial.
Refs #4146, #27303, #30882, #33057
