postprocess: Route namespaced model ids through OpenRouter

OpenRouter is OpenAI-compatible, so reuse GPTModel with its base URL.
Its model ids always contain a slash (vendor/model), which bare
gemini-*/gpt-* ids never do, so dispatch on that instead of
maintaining a vendor list.

Author: thedataking

c2rust-postprocess/postprocess/models/__init__.py

@@ -4,13 +4,18 @@
 from postprocess.models.gemini import GoogleGenerativeModel
 from postprocess.models.gpt import GPTModel
 
+OPENROUTER_BASE_URL = "https://openrouter.ai/api/v1"
+
 
 def api_key_from_env(model_id: str) -> str | None:
     """Retrieve API key from environment variable based on model ID."""
     if model_id.startswith("gemini"):
         return os.getenv("GEMINI_API_KEY")
     elif model_id.startswith("gpt"):
         return os.getenv("OPENAI_API_KEY")
+    # OpenRouter ids are namespaced, e.g. "anthropic/claude-sonnet-4.5"
+    elif "/" in model_id:
+        return os.getenv("OPENROUTER_API_KEY")
     return None
 
 
@@ -20,5 +25,11 @@ def get_model_by_id(id: str) -> AbstractGenerativeModel:
         return GoogleGenerativeModel(id=id)
     elif id.startswith("gpt"):
         return GPTModel(id=id)
+    elif "/" in id:
+        return GPTModel(
+            id=id,
+            api_key=os.getenv("OPENROUTER_API_KEY"),
+            base_url=OPENROUTER_BASE_URL,
+        )
 
     raise ValueError(f"Unsupported model identifier: {id}")