Keep the first non-zero exit code instead of summing

Summing can land on a multiple of 256: two phases failing with 128 each summed
to 256 and exited 0, reporting success. Keeping the first non-zero code also
makes the exit status identify the phase that failed. The static guard in
test/tests/ now checks that neither site sums again.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

Author: sawenzel

test/tests/exit_code_aggregation.sh

@@ -1,8 +1,11 @@
 #!/bin/bash
-# Static guard against the exit-code-aggregation bug in run_workflow_tests.sh:
-# the final RET=$(( ... )) line must include every aggregate return-code
-# variable the script computes, and each of those variables must actually be
-# assigned somewhere in the script.
+# Static guard against the exit-code-aggregation bugs in run_workflow_tests.sh.
+# Two things must hold:
+#   1. the final RET= line must reference every aggregate return-code variable
+#      the script computes, and each must actually be assigned somewhere;
+#   2. no exit code may be produced by *summing* codes. Sums can land on a
+#      multiple of 256 — two phases failing with 128 each sum to 256, which
+#      exits 0 — so a real failure would report success.
 
 set -u
 HERE=$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)
@@ -25,7 +28,7 @@ check()
 # whoever adds it come here and update this list.
 REQUIRED_VARS="ret_global_pwg ret_analysis_qc ret_global_anchored"
 
-RET_LINE=$(grep -m1 -E '^RET=\$\(\(' "${SCRIPT}")
+RET_LINE=$(grep -m1 -E '^RET=' "${SCRIPT}")
 
 for var in ${REQUIRED_VARS} ; do
     present=$(grep -c -- "${var}" <<< "${RET_LINE}")
@@ -37,6 +40,13 @@ for var in ${REQUIRED_VARS} ; do
     check "${var} is assigned in the script" 1 "$( [[ "${assigned}" -ge 1 ]] && echo 1 || echo 0 )"
 done
 
+# No exit code may be a sum of codes. These are the two sites that had it.
+summed_ret=$(grep -c -E '^RET=\$\(\(' "${SCRIPT}")
+check "RET is not a sum of codes" 0 "${summed_ret}"
+
+summed_this=$(grep -c -E 'ret_this=\$\(\(ret_this[[:space:]]*\+' "${SCRIPT}")
+check "test_single_wf does not sum codes" 0 "${summed_this}"
+
 echo
 if [[ "${FAILURES}" == "0" ]] ; then
     echo "All exit-code aggregation checks passed"