When an auxiliary task is configured with provider=custom and an explicit
base_url but an empty api_key, the custom_key fallback chain in
resolve_provider_client() jumped straight to the no-key-required
placeholder without consulting model.api_key from config.yaml. Users
on self-hosted gateways who share the same endpoint and credentials for
both the main model and auxiliary tasks got 401 auth errors.
Add _read_main_api_key() following the same pattern as _read_main_model()
and _read_main_provider(): checks _RUNTIME_MAIN_API_KEY (runtime override)
first, then config.yaml model.api_key. Insert it into the fallback chain
before no-key-required so real credentials are used when available, while
local servers without auth still get the placeholder.
Tranquil-Flow
8e09afda27