Sod iso test for compressible hydro

[glesur]

No description provided.

[Copilot]

Pull request overview

This PR adds an isothermal Sod shock-tube regression test for the compressible_hydro RHS, and introduces new physics knobs (eta_rho, rho_floor) to support stable compressible runs and validation in CI.

Changes:

• Add a new test/sod-iso test (init script, INI config, and validation against an analytic Sod solution) and wire it into GitHub Actions (serial + MPI).
• Extend CompressibleHydro with optional density diffusion (eta_rho) and a density floor used to avoid division-by-zero in the real-space nonlinear “windup”.
• Update input-file documentation to describe the new compressible_hydro parameters, and adjust Python embedding signal handling.

Reviewed changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
test/sod-iso/validate.py	New validator comparing simulation output against analytic Sod solution (found a brittle slicing bug).
test/sod-iso/sod_test.py	New Python init condition for the Sod isothermal setup.
test/sod-iso/astra.ini	New runtime configuration for the Sod isothermal compressible hydro test.
src/rightHandSide/compressible_hydro.hpp	Adds eta_rho diffusion in ImplicitStep and uses rho_floor during real-space nonlinear term construction.
src/astrapy.cpp	Restores default SIGINT handling after initializing the embedded Python interpreter.
pytools/sod.py	Adds an analytic Sod solver (but currently uses exit() on invalid inputs).
doc/source/input_file.rst	Documents eta_rho and rho_floor (one formula needs correction to reference rho, not v).
.github/workflows/astra-ci-jobs.yml	Runs the new sod-iso test in Serial and Parallel CI jobs.

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