Get a rule by ID.

Returns the latest version when version is omitted; pass a version number to
fetch a specific revision. The rule must belong to your session organization.

query_for_latest_trigger=true adds meta.latest_trigger — the same payload
POST /rules/most-recent-trigger returns, for this rule alone. The lookup fails open:
if the engine is unavailable the rule still comes back and meta.latest_trigger
reports the failure itself (empty data, null meta, reason in
meta.latest_trigger.error).