Discovers test/wcc/data, hard-pins corpus identity (1,224 fixtures,
314 error / 12 compile / 136 run / 762 run-exit, sha256 name hash),
schedules both frontend cells per fixture through os.exec with
per-cell capture dirs, and emits the strict wwfix TSV result stream.
integration.sh is the black-box owner of the CLI/protocol boundary.
Captured-async start/poll/cancel plus inherited-stdio run/runstdio with
process-group creation, close-on-exec errno marker for exec-setup
failure, TERM-grace-KILL escalation, and a signalfd interrupt watch.
test/wwfixture/process/main.ww is its self-exec harness, built by both
driver stages.
