N1-1: writeback scope verified too broad (any chosen, incl. shadow
applied=False, worker_default and worker_explicit) and narrowed to
source=policy + applied only; writeback now records a
worker_model_persisted audit row as the identity marker.
N1: persisted models are rechecked against current tier requires
before dispatch on later attempts (fixes4 split known/unknown):
active + known-missing fails fast (worker_capability_recheck_
rejected, no runner), unknown-only and shadow only audit.
User-explicit, worker-CLI-explicit and gateway-filled tasks skip
the recheck; legacy models are recognised by a policy applied
worker_routing row. Recheck never rewrites tasks.model and never
re-decides.
