Salvaged from PR #57342 by @liuhao1024 (with the injection-scan half
from PR #57360 by @ghedeselmabot): cronjob(action='run', prompt=...)
silently discarded the prompt argument — per-run context never
reached the spawned cron session.
The prompt is now threaded as extra_prompt through the whole chain
(cronjob run action → _try_dispatch_background_run/_execute_job_now →
_run_claimed_job → run_one_job → run_job → _build_job_prompt) and
appended to the stored prompt under a '## Run Context' header for
that single fire only — never persisted to the job definition. It
passes the same strict _scan_cron_prompt injection scan as stored
prompts before firing, and works identically on the background and
sync fallback paths.
Test fakes across tests/cron/ updated to accept the new kwargs
(sibling-test blast radius from the signature change).
Co-authored-by: liuhao1024 <liuhao1024@users.noreply.github.com>
