Go 1.26.5 maps each test binary's stdout and stderr to the same product writer. Teach the captured executor to share one open file description for byte-equal output paths, then make directory test products emit that one ordered capture on coordinator stdout. Build captures and inherited-stdio routes remain unchanged.\n\nKeep the executor mechanism, package policy, native Cstage/WWstage proof, and normative contract together so every commit preserves the observable test-output behavior.
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.
