Multi-domain mesh creation

Hello.
I have data that is distributed amongst N processes and I want to create a blueprint mesh for it. I thought I was doing it correctly, but when I call the partition function, I am getting unexpected results. I'm not sure if I am creating the mesh wrong or calling the partition function wrong.
Any assistance would be appreciated!

Example (12 processes, each owning a 4x4 subregion of an overall 16x12 grid):

+-----+-----+-----+-----+
|  0  |  1  |  2  |  3  |
|     |     |     |     |
+-----+-----+-----+-----+
|  4  |  5  |  6  |  7  |
|     |     |     |     |
+-----+-----+-----+-----+
|  8  |  9  | 10  | 11  |
|     |     |     |     |
+-----+-----+-----+-----+

Code:

int rows = 3;
int columns = 4;
int local_width = 4;
int local_height = 4;
int row = rank / columns;
int column = rank % columns;
int origin_x = local_width * column;
int origin_y = local_height * row;

double values[16] = {...};

conduit::Node mesh;
mesh["state/domain_id"] = process_id;

mesh["coordsets/coords/type"] = "uniform";
mesh["coordsets/coords/dims/i"] = local_width;
mesh["coordsets/coords/dims/j"] = local_height;

mesh["coordsets/coords/origin/x"] = origin_x;
mesh["coordsets/coords/origin/y"] = origin_y;
mesh["coordsets/coords/spacing/dx"] = 1;
mesh["coordsets/coords/spacing/dy"] = 1;

mesh["topologies/topo/type"] = "uniform";
mesh["topologies/topo/coordset"] = "coords";

mesh["fields/scalar1/association"] = "vertex";
mesh["fields/scalar1/topology"] = "topo";
mesh["fields/scalar1/values"].set(values, 16);

I then want to repartition the mesh to access the whole thing on process 0. So I tried the following:

conduit::Node options, selections, output;
conduit::Node &selection = selections.append();
selection["type"] = "logical";
selection["start"] = {0u, 0u, 0u}; // for some reason this failed if I only used 2 dimensions
selection["end"] = {16u, 12u, 1u}; // for some reason this failed if I only used 2 dimensions
options["target"] = 1;
options["selections"] = selections;

conduit::blueprint::mpi::mesh::partition(mesh, options, output, MPI_COMM_WORLD);

However, the resulting output mesh still only has size 4x4 and only contains the data from process 0.

As a side note, I am setting "target" to 1 (specifying 1 process), but how do I specify which process (i.e. what if I want it on process 3 instead of process 1)?

Start by reproducing the 12-process example and tracing the call to conduit::blueprint::mpi::mesh::partition with the shown options and selections. Inspect the resulting mesh on the target process and determine how the target rank and logical selection are expected to work. Done means documenting or correcting the behavior so the full 16x12 mesh is available on the requested process.