BENCH: add large-file high-thread OOM/scaling probe

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: jbrockmendel

.github/workflows/bench-read-csv-windows.yml

@@ -78,6 +78,16 @@ jobs:
             --fixtures "$FIX" --threads "$THR" --reps "$REPS" $ROWS_ARG \
             --out bench-results.json | tee bench-stdout.txt
 
+      - name: OOM / high-thread probe
+        # Large (~1.4 GB) file swept up to 12 threads to check peak working-set
+        # scaling and whether the T=12 OOM from GH#64347 still occurs.
+        if: ${{ github.event.inputs.rows == '' }}
+        shell: bash
+        run: |
+          pixi run --environment py313 python scripts/bench_read_csv_parallel.py \
+            --fixtures ints --threads 1,2,4,8,12 --reps 3 --rows 15000000 \
+            --out bench-oom.json | tee bench-oom-stdout.txt
+
       - name: Write step summary
         if: always()
         shell: bash
@@ -97,3 +107,5 @@ jobs:
           path: |
             bench-results.json
             bench-stdout.txt
+            bench-oom.json
+            bench-oom-stdout.txt