stop()'s drain grouped api_server (/v1) runs with chat turns on the
restart_drain_timeout budget, which defaults to 0. A default-config stop
therefore never entered the drain loop and hard-interrupted every
in-flight /v1 run after 0.00s, even though a caller is blocked on its
result and nothing resumes it. #82161 split only cron off onto its own
watchdog-clamped floor (agent.cron_drain_timeout).
Let api_server runs ride that same clamped floor (no new config key);
chat turns and deferred post-turn workers stay on the chat budget, and
cron_drain_timeout: 0 still opts out. Reuses the existing
_active_api_run_count counter via _drain_work_counts.
Fixes#132989. Diagnosis and the 'ride the cron deadline' approach by
the reporter, @ItoDonno.
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