A typed `/model <name>` where `<name>` is declared under `providers.<slug>` or
`custom_providers` — but typed while the current provider is a soft-accepting
one (e.g. `openai-codex`) — stayed on the current provider and was swallowed as
an unknown hidden Codex model, instead of routing to the provider that actually
declares it.
Add configured-provider exact-match detection (`_configured_provider_matches`)
and a new Step d.5 in `switch_model`: if the typed model is declared in
user/custom provider config, route to that provider BEFORE
`detect_provider_for_model()` guesses from static catalogs and BEFORE the
common-path validation lets a soft-accepting current provider swallow the name.
- Matching is exact (case-insensitive) against explicitly-declared model
collections only (`models`, `model`, `default_model`) — never fuzzy/family.
- Same-provider declarer → keep current provider (canonicalize the id).
- Multiple declarers → fail clearly and ask for `--provider <slug>`.
- Single declarer → route there; for `providers.<slug>` user providers, set
`explicit_provider` so the credential block resolves base_url/key from config.
- Step e (`detect_provider_for_model`) is gated off when `config_routed`.
The deliberately-supported openai-codex / xai-oauth hidden-model soft-accept
(#16172 / #19729) is left untouched: when nothing in config matches, detection
is a no-op.
Salvaged from #45442 by harjothkhara (authorship preserved).
Tests: tests/hermes_cli/test_model_switch_configured_provider_routing.py
(7 tests). Full model_switch suite: 214 passed.
Fixes#45006
harjothkhara