Follow-up to srojk34's explicit-provider unwrap (PR #56691):
- Extract _resolve_moa_aggregator() as the single preset->aggregator
resolver shared by _resolve_auto(), _resolve_task_provider_model(),
and resolve_provider_client() so preset lookup/validation can't drift.
- When the main provider is moa, the aggregator model is now the default
for every UNSET auxiliary model: _read_main_model_for_aux() substitutes
the preset's acting (aggregator) model wherever fallback chains
pre-filled from _read_main_model() (router prefill, custom-endpoint
fallback, named-custom default, external-process default,
_try_main_agent_model_fallback).
- Unwrap moa at the resolve_provider_client() chokepoint so direct
callers (vision auto-detect, plugin code) can't dead-end in the
unknown-provider branch, and unwrap the vision auto-detect main
provider before capability probes run against the preset name.
- Real-config tests: temp HERMES_HOME + actual config.yaml exercising
the genuine load_config()/resolve_moa_preset() boundary.
2755bf558e