Fix CI edge cases: guard os.remove, skip bare -- flag, use -s for empty file check

- Wrap os.remove() in try/except OSError on abort path so permission errors
  don't mask the real MFCException
- Only pass --precision flag when matrix.precision is non-empty to avoid
  invalid bare -- argument
- Use -s instead of -f for failed_uuids.txt to skip retry when file exists
  but is empty

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

Author: sbryngelson

.github/workflows/test.yml

@@ -138,7 +138,7 @@ jobs:
 
       - name: Build
         run:  |
-          /bin/bash mfc.sh test -v --dry-run -j "$(nproc)" --${{ matrix.debug }} --${{ matrix.mpi }} --${{ matrix.precision }} $TEST_ALL
+          /bin/bash mfc.sh test -v --dry-run -j "$(nproc)" --${{ matrix.debug }} --${{ matrix.mpi }} ${{ matrix.precision != '' && format('--{0}', matrix.precision) || '' }} $TEST_ALL
         env:
           TEST_ALL: ${{ matrix.mpi == 'mpi' && '--test-all' || '' }}
 
@@ -149,7 +149,7 @@ jobs:
           /bin/bash mfc.sh test -v --max-attempts 3 -j "$(nproc)" $TEST_ALL $TEST_PCT || TEST_EXIT=$?
 
           # Retry only if a small number of tests failed (sporadic failures)
-          if [ -f tests/failed_uuids.txt ]; then
+          if [ -s tests/failed_uuids.txt ]; then
             NUM_FAILED=$(wc -l < tests/failed_uuids.txt)
             if [ "$NUM_FAILED" -gt 0 ] && [ "$NUM_FAILED" -le 5 ]; then
               FAILED=$(cat tests/failed_uuids.txt | tr '\n' ' ')

toolchain/mfc/test/test.py

@@ -192,8 +192,11 @@ def test():
     if abort_tests.is_set():
         # Clean up stale failed_uuids.txt so CI doesn't retry wrong tests
         failed_uuids_path = os.path.join(common.MFC_TEST_DIR, "failed_uuids.txt")
-        if os.path.exists(failed_uuids_path):
-            os.remove(failed_uuids_path)
+        try:
+            if os.path.exists(failed_uuids_path):
+                os.remove(failed_uuids_path)
+        except OSError:
+            pass
 
         total_completed = nFAIL + nPASS
         cons.print()