Separate version set for simulation part (generator, halld_sim, hdgeant4)

[aaust]

Since the move to jana2, we are no longer able to compile "recon-compatible" version sets which combine halld_recon from the time of the REST production with recent versions of halld_sim and hdgeant4. For that reason, these version sets have last been updated in Fall 2024.

In order to be able to improve our simulation or use recent additions to the generator suite, we need a possibility to select a separate xml file for the simulation part. The default should be the latest official release (currently 7.2.0) for all run periods. The recon version set should only be used for the REST production step.

The guidelines have to be updated, too.

[s6pepaul]

What is needed is two-fold.
Step 1: Add a SIM_ENVIRONMENT variable to MCWrapper that contains the environment for the steps generation, postgen, geant and mcsmear. Then one only has to modify the runGen , ... commands (

gluex_MCwrapper/MakeMC.sh

Line 372 in fa05530

runGen=''

and following)
Everything else should be in place already. That should allow the user to run separate environments for simulation, reconstruction and tree generation

Step 2: Add this to the webform. This requires also changes to MCWrapperFE and the database.

@andrsmit Can you take a stab at 1?
@T-Britton can you prepare the backend for 2?

[jrstevenjlab]

This is a pretty significant need for us to be able to generate new MC for all the GlueX-I and 2020 datasets with the latest updates to the generators and simulation packages (using the older halld_recon for reconstruction). I hope we can get this implemented in early 2026