Scott Glover's commit 371b69b3e2 ('Expose cron jobId in plugin hook
context') added an optional jobId field on PluginHookAgentContext,
populated for cron-driven runs. The commit shipped without a docs
update or CHANGELOG entry, so plugin authors had no visible signal
that the new ctx.jobId field exists.
Surface ctx.jobId in two existing hook context references in
docs/plugins/hooks.md: the before_tool_call ctx-fields list, and the
runId/agent-lifecycle paragraph that already names ctx.runId — extend
it to note ctx.jobId on cron-driven runs and what plugins can do with
it (scope metrics, side effects, or state to a scheduled job).
Expose first-class hook correlation fields for plugin message and run lifecycle hooks, including frozen diagnostic trace copies for plugin-facing events.
