When the user composes a template that already has compositions of its
own (e.g. \$Sensor → Probe1 slot), only the outer derived was created
— the source's children weren't replicated. AddCompositionAsync now
walks the source's composition graph and creates a parallel derived for
every slot it encounters, each linked back through ParentTemplateId so
override chains stay intact (\$Probe → \$Sensor.Probe1 → \$Pump.TempSensor.Probe1).
The cascade pre-flights every name it would create — a deep collision
aborts before any rows mutate. Internal helper
CreateCascadedCompositionAsync skips the "base templates only" check
since it operates on the source side which may legitimately reference
derived rows.
Joseph Doherty
4f90f952d0