The section is a strict subset of the plugin config: `agents` is consumed
once when the service starts, so a stored change there could only look like
it had an effect. The cap resolves through a getter over the settings source,
which the scheduler destructures at the start of each tool group, so a
committed change bounds the next group without disturbing the one in flight.
`resolveMaxParallelToolCalls` becomes the section validator, refusing a value
at the write instead of at that group.
The deferred-resume effect-shape assertion now allows the one plugin effect
the optional settings wiring adds at the fiber's own level; a resumed agent
joining it there is still the regression it pins.
fdf9bddbf8