When config has provider=openrouter and model=openrouter/free,
resolve_model_provider() stripped the 'openrouter/' prefix because
prefix == config_provider. This sent 'free' to OpenRouter's API,
which returned 404 (model not found).
OpenRouter always needs the full provider/model path (e.g.
openrouter/free, anthropic/claude-sonnet-4.6). The prefix-stripping
logic is only correct for direct-API providers.
Fix: skip prefix stripping entirely when config_provider is 'openrouter'.
Return the full model_id with provider='openrouter'.
Added 7 unit tests for resolve_model_provider() covering:
- openrouter/free keeps full path (the bug)
- openrouter cross-provider models keep full path
- direct API providers still strip prefix correctly
- cross-provider routing to openrouter
- bare model names use config provider
- empty model returns defaults
Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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