fix(fallback): let custom_providers shadow built-in aliases#18185
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When a user defines `custom_providers: [{name: kimi, ...}]` and references
`provider: kimi` from fallback_model or the main config, the built-in alias
rewriting (`kimi` → `kimi-coding`) was hijacking the request before the
named-custom lookup ran. `_get_named_custom_provider` also refused to
return a match when the raw name resolved to any built-in (including aliases),
so the custom endpoint was unreachable.
Fix at both layers of the resolution chain so every caller benefits, not
just `_try_activate_fallback`:
- hermes_cli/runtime_provider.py: narrow `_get_named_custom_provider`'s
built-in-wins guard to canonical provider names only. An alias like
`kimi` that resolves to a different canonical (`kimi-coding`) no longer
blocks the custom lookup; a canonical name like `nous` still does.
- agent/auxiliary_client.py: in `resolve_provider_client`, try the named-
custom lookup with the original (pre-alias-normalization) name before the
alias-normalized one, so aliased requests reach the user's custom entry.
Also honour `explicit_base_url` and `explicit_api_key` in the API-key
provider branch so callers that pass explicit hints (e.g. fallback
activation) can override the registered defaults.
Tests added for:
- custom `kimi` shadowing built-in alias (regression for #15743)
- custom `nous` NOT shadowing canonical built-in (behaviour preserved)
- bare `kimi` without any custom entry still routing to built-in
- explicit base_url/api_key override on the API-key provider branch
Original PR #17827 by @Feranmi10 identified the same bug class and
implemented a narrower fix in `_try_activate_fallback`; this reshapes the
fix to live in the shared resolution layer so all callers benefit.
Fixes #15743
Co-authored-by: Feranmi10 <89228157+Feranmi10@users.noreply.github.com>
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This was referenced May 24, 2026
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Summary
When a user defines a
custom_providersentry whose name coincidentally matches a built-in alias (e.g.kimi→kimi-coding), the built-in alias rewriting was hijacking the request before the named-custom lookup ran, so the custom endpoint was unreachable. Fallback activation in particular would silently drop the custom fallback and leave the primary provider's base_url in place.Fixed at the shared resolution layer so every caller benefits —
_try_activate_fallback,resolve_provider_clientfrom auxiliary routing, and_resolve_named_custom_runtimefor main provider resolution — not just the fallback path.Changes
_get_named_custom_provider's built-in-wins guard now only fires for canonical provider names (nous,openrouter, …). Raw names that are aliases to a different canonical (kimi→kimi-coding) no longer block the custom lookup.resolve_provider_clienttries the named-custom lookup with the original (pre-alias-normalization) name before the normalized one. Also honoursexplicit_base_url/explicit_api_keyin the API-key branch so callers that pass explicit hints can override the registered defaults.kimishadowing built-in alias, customnousNOT shadowing canonical (behaviour preserved), barekimiwithout custom still routing to built-in, explicit overrides on the API-key branch.Validation
kimi→ falls backaliyun-singapore→ falls backnouswith shadow customkimiwithout any custom entryFull relevant test suite:
tests/hermes_cli/test_runtime_provider_resolution.py+tests/hermes_cli/test_user_providers_model_switch.py+tests/agent/test_auxiliary_named_custom_providers.py→ 167 passed.Credit
Original PR #17827 by @Feranmi10 identified the same bug class and implemented a narrower fix in
_try_activate_fallback. This reshapes the fix to live in the shared resolution layer so all callers benefit; Feranmi10 is credited viaCo-authored-by:.Fixes #15743
Closes #17827