fix: warn on unsupported request parameters instead of rejecting

Change validate_no_unsupported_fields to log a warning instead of
returning an error when unknown fields are present. This improves
compatibility with clients that send extra parameters like
add_special_tokens, prompt_cache_key, request_id, or chat_template.

https://claude.ai/code/session_01EoHsvxn4B3WMuJkwP5f6od

Author: claude

lib/llm/src/http/service/openai.rs

@@ -2786,17 +2786,9 @@ mod tests {
         assert!(request.unsupported_fields.contains_key("documents"));
         assert!(request.unsupported_fields.contains_key("chat_template"));
 
+        // Unsupported fields should now produce a warning but not an error
         let result = validate_chat_completion_fields_generic(&request);
-        assert!(result.is_err());
-        if let Err(error_response) = result {
-            assert_eq!(error_response.0, StatusCode::BAD_REQUEST);
-            let msg = &error_response.1.message;
-            assert!(msg.contains("Unsupported parameter"));
-            // Verify all fields appear in the error message
-            assert!(msg.contains("add_special_tokens"));
-            assert!(msg.contains("documents"));
-            assert!(msg.contains("chat_template"));
-        }
+        assert!(result.is_ok());
     }
 
     #[test]
@@ -2819,16 +2811,9 @@ mod tests {
         );
         assert!(request.unsupported_fields.contains_key("response_format"));
 
+        // Unsupported fields should now produce a warning but not an error
         let result = validate_completion_fields_generic(&request);
-        assert!(result.is_err());
-        if let Err(error_response) = result {
-            assert_eq!(error_response.0, StatusCode::BAD_REQUEST);
-            let msg = &error_response.1.message;
-            assert!(msg.contains("Unsupported parameter"));
-            // Verify both fields appear in error message
-            assert!(msg.contains("add_special_tokens"));
-            assert!(msg.contains("response_format"));
-        }
+        assert!(result.is_ok());
     }
 
     #[tokio::test]

lib/llm/src/protocols/openai/chat_completions.rs

@@ -426,4 +426,29 @@ mod tests {
             assert_eq!(output_options.skip_special_tokens, Some(skip_value));
         }
     }
+
+    #[test]
+    fn test_unsupported_fields_warn_not_error() {
+        use crate::engines::ValidateRequest;
+
+        let json_str = json!({
+            "model": "test-model",
+            "messages": [{"role": "user", "content": "Hello"}],
+            "add_special_tokens": true,
+            "prompt_cache_key": "key123",
+            "request_id": "req-456",
+            "chat_template": "custom"
+        });
+        let request: NvCreateChatCompletionRequest =
+            serde_json::from_value(json_str).expect("Failed to deserialize request");
+
+        // These fields should be captured as unsupported
+        assert!(request.unsupported_fields.contains_key("add_special_tokens"));
+        assert!(request.unsupported_fields.contains_key("prompt_cache_key"));
+        assert!(request.unsupported_fields.contains_key("request_id"));
+        assert!(request.unsupported_fields.contains_key("chat_template"));
+
+        // Validation should succeed (warn, not error)
+        assert!(ValidateRequest::validate(&request).is_ok());
+    }
 }

lib/llm/src/protocols/openai/validate.rs

@@ -97,7 +97,11 @@ pub const MAX_REPETITION_PENALTY: f32 = 2.0;
 // Shared Fields
 //
 
-/// Validates that no unsupported fields are present in the request
+/// Validates unsupported fields in the request.
+/// Instead of rejecting requests with unsupported fields, this now logs a warning
+/// and allows the request to proceed. This improves compatibility with clients
+/// that send extra parameters (e.g. add_special_tokens, prompt_cache_key,
+/// request_id, chat_template).
 pub fn validate_no_unsupported_fields(
     unsupported_fields: &std::collections::HashMap<String, serde_json::Value>,
 ) -> Result<(), anyhow::Error> {
@@ -106,7 +110,7 @@ pub fn validate_no_unsupported_fields(
             .keys()
             .map(|s| format!("`{}`", s))
             .collect();
-        anyhow::bail!("Unsupported parameter(s): {}", fields.join(", "));
+        tracing::warn!("Ignoring unsupported parameter(s): {}", fields.join(", "));
     }
     Ok(())
 }