Add a regression guard for the dropped-aggregate exit-code bug

This adds a static test that catches an aggregate return-code variable
being dropped from run_workflow_tests.sh's final RET= line, the exact bug
class Task 1 fixed for ret_global_pwg.

- test/tests/exit_code_aggregation.sh checks that RET= includes all three
  known aggregate variables (ret_global_pwg, ret_analysis_qc,
  ret_global_anchored), by an explicit hard-coded list.
- It also checks that each of the three is actually assigned somewhere in
  the script, since a name missing from the RET= line and a name never
  assigned are different bugs with the same symptom.
- No refactor of run_workflow_tests.sh; the guard reads it as a fixture,
  it does not stub or execute it.
- test/README.md now lists the new harness beside run_tests_selection.sh.

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

Author: sawenzel

test/README.md

@@ -73,6 +73,7 @@ exit-code aggregation without needing an O2 environment:
 
 ```bash
 bash test/tests/run_tests_selection.sh
+bash test/tests/exit_code_aggregation.sh
 ```
 
 ### Keeping all test artifacts

test/tests/exit_code_aggregation.sh

@@ -0,0 +1,46 @@
+#!/bin/bash
+# Static guard against the exit-code-aggregation bug in run_workflow_tests.sh:
+# the final RET=$(( ... )) line must include every aggregate return-code
+# variable the script computes, and each of those variables must actually be
+# assigned somewhere in the script.
+
+set -u
+HERE=$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)
+SCRIPT=${O2DPG_TEST_WORKFLOW_SCRIPT:-"${HERE}/../run_workflow_tests.sh"}
+FAILURES=0
+
+check()
+{
+    local label=$1 expected=$2 actual=$3
+    if [[ "${expected}" == "${actual}" ]] ; then
+        echo "ok   - ${label}"
+    else
+        echo "FAIL - ${label}: expected '${expected}', got '${actual}'"
+        FAILURES=$((FAILURES + 1))
+    fi
+}
+
+# The three aggregate return-code variables the final exit code must include.
+# Explicit and hard-coded on purpose: a fourth aggregate added later must make
+# 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}")
+
+for var in ${REQUIRED_VARS} ; do
+    present=$(grep -c -- "${var}" <<< "${RET_LINE}")
+    check "RET= line includes ${var}" 1 "${present}"
+done
+
+for var in ${REQUIRED_VARS} ; do
+    assigned=$(grep -c -E "^[[:space:]]*${var}=" "${SCRIPT}")
+    check "${var} is assigned in the script" 1 "$( [[ "${assigned}" -ge 1 ]] && echo 1 || echo 0 )"
+done
+
+echo
+if [[ "${FAILURES}" == "0" ]] ; then
+    echo "All exit-code aggregation checks passed"
+else
+    echo "${FAILURES} test(s) failed"
+fi
+exit $(( FAILURES > 0 ? 1 : 0 ))