ci: always nuke build/ on Phoenix to avoid stale ISA mismatches

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

Author: Spencer Bryngelson

.github/workflows/common/test.sh

@@ -10,14 +10,10 @@ build_opts="$gpu_opts"
 
 # --- Build (if not pre-built on login node) ---
 # Phoenix builds inside SLURM; Frontier pre-builds via build.sh on the login node.
-# Phoenix: validate an existing build against this node's CPU ISA.
-# A stale build/ from a prior run on a different microarchitecture would SIGILL.
-if [ "$job_cluster" = "phoenix" ] && [ -d "build" ]; then
-    syscheck_bin=$(find build/install -name syscheck -type f 2>/dev/null | head -1)
-    if [ -n "$syscheck_bin" ] && ! "$syscheck_bin" > /dev/null 2>&1; then
-        echo "syscheck failed on existing build — nuking build/"
-        rm -rf build
-    fi
+# Phoenix builds inside SLURM on heterogeneous compute nodes — always start fresh
+# to avoid SIGILL from stale binaries compiled on a different microarchitecture.
+if [ "$job_cluster" = "phoenix" ]; then
+    rm -rf build
 fi
 
 if [ ! -d "build" ]; then