[Users] Carpet: How to turn off auto-prolongation for 'mesh-refinement ghosts'?

[Scott Hawley]

My thorn BruiserSetBG saves a background spacetime which is then used by
the solver thorn BruiserConstraints.

The background is set via an analytic expression, even in the regions
designated as ghost zones.  The ones I'm concerned about in this e-mail
are not inter-processor ghost zones, rather they are regions which (for
all OTHER gridfunctions) are typically filled in via prolongation from a
coarser grid.

But for the background, I don't want this prolongation to occur, and it's
happening automatically without my specifying to do so.

BrusierSetBG is created in local mode, thus I'm not explicitly calling any
sync operation, but the ghost info is getting overwritten before the data
makes it to BrusierConstraints.  Presumably this sync is being called
inside the flesh/scheduler.    BruiserConstraints is a global thorn.

Question:  Is there any way to specify that, for a particular set of grid
functions (i.e. the background spacetime), no prolongation is to occur?  I
haven't seen a parameter that does this.

I am open to re-writing BrusierSetBG as a 'global' thorn if that will make
a difference.   Otherwise perhaps I'll create a thorn called "BrusierBoth"
or something, that feeds the background straight into the solver.

Thanks very much,
Scott