Function launch_session_handling_sigterm 

pub fn launch_session_handling_sigterm(
    staged: StagedSession,
    on_url: impl FnOnce(&str),
) -> Result<LaunchResult, RuntimeError>

launch_session for a process whose lifetime is this one session.

On unix an agent session takes SIGTERM over for the rest of the process: the first signal cancels every live task and ends the session through its normal teardown, a second exits at once with status 143, and [TERMINATE_TEARDOWN_DEADLINE] after the first the process exits with status 143 whatever it is doing. Those exits end the whole process, so nothing that outlives the session may share it. A script capsule, or a platform without SIGTERM, launches exactly as launch_session does.

It is also the one launch that honours a lifeline:

• A formation lifeline (StagedSession::attach_formation_lifeline): EOF on it begins the same termination a first SIGTERM does, after appending formation_ended to the trace, and never counts as a SIGTERM. Every other launch of a session holding one, and this one for a script capsule, is refused with RuntimeError::FormationLifelineUnreadable.
• A spawner lifeline (StagedSession::attach_spawner_lifeline): on an agent capsule, EOF on it begins that termination after appending spawner_ended, on the same terms. A script capsule takes no SIGTERM handler, so there EOF does what a SIGTERM does to it: the process exits with status 143. Every other launch of a session holding one is refused with RuntimeError::SpawnerLifelineUnreadable.

Whichever lifeline closes first while nothing else has begun the termination is the one whose record is written.