[xylar]

Since 2.2.0, planar meshes label latCell, lonCell, latEdge, lonEdge, latVertex and lonVertex with standard_name: latitude or longitude. On a planar mesh these are all zero and are not geographic coordinates, so CF-aware tools shouldn't treat them as such.

This PR:

• moves these standard names out of MESH_VAR_ATTRS into a new SPHERE_VAR_ATTRS in mpas_tools.mesh.attrs, and adds get_mesh_var_attrs(on_a_sphere) to combine the two
• has add_mesh_attrs() add them only when on_a_sphere is YES. On planar meshes it also removes these standard names if present, so that planar meshes made with 2.2.0 get cleaned up.
• has MpasMeshConverter.x and MpasCellCuller.x write them only for spherical meshes
• updates the CF tests to check that planar meshes have no lat/lon standard names and spherical meshes do

Fixes #770

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Posted by Claude Code on @xylar's behalf. The testing, analysis and wording above are AI-authored; please check them accordingly.

🤖 Generated with Claude Code

[xylar]

Testing

Because this PR changes MpasMeshConverter.x and MpasCellCuller.x, I built the package locally with rattler-build (ci/linux_64_python3.14.____cpython.yaml) and installed it into the pixi environment from conda_package/pixi.toml.

With that build, the reproducer from #770, extended through cull() and convert() and to a spherical mesh, gives:

Mesh	Step	on_a_sphere	lat/lon standard_name
planar hex (4x4, nonperiodic)	make_planar_hex_mesh()	NO	none
	cull()	NO	none
	convert()	NO	none
mesh.QU.1920km.151026.nc	convert()	YES	latitude / longitude
	cull()	YES	latitude / longitude

From the repo root, pytest conda_package/tests gives 78 passed and 2 failed. The failures are test_pyproject_matches_recipe and test_pyproject_has_no_extra_dependencies in test_dependencies.py. They flag dask in pyproject.toml vs. dask-core in the recipe, and neither file is changed here. The updated tests in test_cf_attrs.py check that planar meshes have no lat/lon standard names after cull() and convert(), that the spherical mesh keeps them after convert(), and that add_mesh_attrs() removes them from a planar mesh and adds them to a spherical one. All of these pass.

pre-commit passes.

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Posted by Claude Code on @xylar's behalf. The testing, analysis and wording above are AI-authored; please check them accordingly.