Deadline of a shell act when [shell].timeout-ms is unset. A shell act
without a deadline holds its scheduler lane for as long as the script runs:
a script that waits forever takes an unbounded share of the engine’s job
capacity with it.
Largest [shell].max-output-bytes accepted. The capture is held in memory
and becomes the act’s output vars, so it is bounded well below what the
machine could hold.
Largest [shell].timeout-ms accepted: the platform’s ceiling on how long
one act may hold a lane. A longer wait belongs in a workflow-level timeout
or a message act, not in a blocking shell act.