Fix Codex provider routing for GitHub Copilot models

nanobot/providers/litellm_provider.py

@@ -88,10 +88,21 @@ class LiteLLMProvider(LLMProvider):
         # Standard mode: auto-prefix for known providers
         spec = find_by_model(model)
         if spec and spec.litellm_prefix:
+            model = self._canonicalize_explicit_prefix(model, spec.name, spec.litellm_prefix)
             if not any(model.startswith(s) for s in spec.skip_prefixes):
                 model = f"{spec.litellm_prefix}/{model}"
-        
+
         return model
+
+    @staticmethod
+    def _canonicalize_explicit_prefix(model: str, spec_name: str, canonical_prefix: str) -> str:
+        """Normalize explicit provider prefixes like `github-copilot/...`."""
+        if "/" not in model:
+            return model
+        prefix, remainder = model.split("/", 1)
+        if prefix.lower().replace("-", "_") != spec_name:
+            return model
+        return f"{canonical_prefix}/{remainder}"
     
     def _apply_model_overrides(self, model: str, kwargs: dict[str, Any]) -> None:
         """Apply model-specific parameter overrides from the registry."""