Document hermes.gateway.background_work in the export table, and add a
'Maintaining and extending this plane' section: the content-free
invariant, and per-change checklists for adding a metric, a new
subsystem, extending the error-class/status/source/state enums, and
adding a content-free span attribute. Each calls out the layers that
silently drop an undeclared signal (observable metric_names registration,
the emitter keep_by_kind allowlist, the closed enums, and any collector
name/keep_keys allowlist) plus whole-chain verification.
Victor Kyriazakos
b49b78b738