Run the guard from a batch script

Use this when the site has not installed the TaskProlog. For srun steps, see Use the guard without changing the site TaskProlog. At the top of the batch script:

eval "$(eessi-arch-guard --shell)"

Stdout is export and unset with values quoted for bash. The human message goes to stderr, so the command substitution captures only the assignments.

docs/examples/shell_demo.py builds the same zen4-loaded, zen2-node stack as the tutorial, runs --shell, and evals the stdout in bash --noprofile --norc.

$ python3 docs/examples/shell_demo.py

case: shell
command: python3 -I src/eessi_arch_guard.py --shell
exit: 0
--- stdout ---
export EBROOTR=$PREFIX/prefix/software/linux/x86_64/amd/zen2/software/R/4.4.2
export EESSI_ACCEL_SUBDIR=''
export EESSI_ARCH_GUARD_RELOADED='x86_64/amd/zen4->x86_64/amd/zen2'
export EESSI_SOFTWARE_SUBDIR=x86_64/amd/zen2
export MODULEPATH=$PREFIX/prefix/software/linux/x86_64/amd/zen2/modules/all
export PATH=$PREFIX/prefix/software/linux/x86_64/amd/zen2/software/R/4.4.2/bin:$PREFIX/prefix/software/linux/x86_64/amd/zen2/bin:$PREFIX/bin:/usr/bin:/bin
export _LMFILES_=''
export _ModuleTable001_=table-for-x86_64-amd-zen2
--- stderr ---
eessi-arch-guard: reloaded modules for x86_64/amd/zen2 (loaded for x86_64/amd/zen4)
--- eval ---
x86_64/amd/zen2
x86_64/amd/zen4->x86_64/amd/zen2

The eval block is what the shell sees after applying stdout. EESSI_SOFTWARE_SUBDIR is the node, and EESSI_ARCH_GUARD_RELOADED records the change. There is no print line: that directive belongs to the prolog protocol.

This eval fixes the shell that runs it. srun ./a.out from that shell inherits the corrected environment only when the srun is started after the eval and the export reaches the step. A bare exec that never passed through the shell still has the submitting environment. The TaskProlog install is the path that runs before execve.

Refuse a failed restore before the payload

An opt-in job wrapper can use strict status instead of interpreting stderr:

if delta="$(/usr/bin/python3 -I /absolute/path/eessi_arch_guard.py --strict --shell)"; then
    eval "$delta"
else
    exit "$?"
fi

The source path names the installed guard file. The native Python interpreter starts before any inherited EESSI Python. A nonzero guard status prevents the payload from running. This does not alter the configured site TaskProlog.