The previous approach of prepending 'openrouter/' to the model ID in the
catalog was incorrect — it only masked the symptom while regressing the
config_provider=openrouter codepath.
The root cause is in resolve_model_provider(): rsplit(':', 1) on
'@openrouter:tencent/hy3-preview:free' yields provider='openrouter:tencent/hy3-preview'
and model='free', because the ':free' suffix collides with the @provider:model
grammar.
Fix: after rsplit, validate that the extracted provider hint is a known
provider (in _PROVIDER_MODELS, _PROVIDER_DISPLAY, or starts with 'custom:').
If not, fall back to split(':', 1) so trailing suffixes stay attached to
the model ID.
This fixes all current and future OR models with colon-suffixed tags
(:free, :beta, :thinking, :nitro, etc.) without catalog changes.
Also adds regression tests for the affected models and edge cases.
Co-authored-by: nesquena-hermes <nesquena-hermes@users.noreply.github.com>
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