Fix job slug collision for sharded Frontier jobs

When two shards (1/2 and 2/2) of the same device/interface pair run
concurrently, they generate identical job_slug values and therefore
identical SBATCH -o output file names, causing concurrent writes to
the same file.

Append a shard suffix (e.g. "-1-of-2") to job_slug when $4 is set,
making output files unique per shard. Non-sharded jobs (empty $4)
are unaffected.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: sbryngelson

.github/workflows/frontier/submit.sh

@@ -28,7 +28,8 @@ else
 fi
 
 
-job_slug="`basename "$1" | sed 's/\.sh$//' | sed 's/[^a-zA-Z0-9]/-/g'`-$2-$3"
+shard_suffix=$([ -n "$4" ] && echo "-$(echo "$4" | tr '/' '-of-')" || echo "")
+job_slug="`basename "$1" | sed 's/\.sh$//' | sed 's/[^a-zA-Z0-9]/-/g'`-$2-$3${shard_suffix}"
 output_file="$job_slug.out"
 
 submit_output=$(sbatch <<EOT

.github/workflows/frontier_amd/submit.sh

@@ -28,7 +28,8 @@ else
 fi
 
 
-job_slug="`basename "$1" | sed 's/\.sh$//' | sed 's/[^a-zA-Z0-9]/-/g'`-$2-$3"
+shard_suffix=$([ -n "$4" ] && echo "-$(echo "$4" | tr '/' '-of-')" || echo "")
+job_slug="`basename "$1" | sed 's/\.sh$//' | sed 's/[^a-zA-Z0-9]/-/g'`-$2-$3${shard_suffix}"
 output_file="$job_slug.out"
 
 submit_output=$(sbatch <<EOT