Add code field and unify error responses for router (#15028)

sgl-model-gateway/src/routers/error.rs

@@ -5,88 +5,156 @@ use axum::{
 };
 use serde_json::json;
 
-pub fn internal_error(message: impl Into<String>) -> Response {
+pub fn internal_error(code: impl Into<String>, message: impl Into<String>) -> Response {
-    create_error(StatusCode::INTERNAL_SERVER_ERROR, "internal_error", message)
+    create_error(StatusCode::INTERNAL_SERVER_ERROR, code, message)
 }
 
-pub fn bad_request(message: impl Into<String>) -> Response {
+pub fn bad_request(code: impl Into<String>, message: impl Into<String>) -> Response {
-    create_error(StatusCode::BAD_REQUEST, "invalid_request_error", message)
+    create_error(StatusCode::BAD_REQUEST, code, message)
 }
 
-pub fn not_found(message: impl Into<String>) -> Response {
+pub fn not_found(code: impl Into<String>, message: impl Into<String>) -> Response {
-    create_error(StatusCode::NOT_FOUND, "invalid_request_error", message)
+    create_error(StatusCode::NOT_FOUND, code, message)
 }
 
-pub fn service_unavailable(message: impl Into<String>) -> Response {
+pub fn service_unavailable(code: impl Into<String>, message: impl Into<String>) -> Response {
-    create_error(
+    create_error(StatusCode::SERVICE_UNAVAILABLE, code, message)
-        StatusCode::SERVICE_UNAVAILABLE,
-        "service_unavailable",
-        message,
-    )
 }
 
-pub fn failed_dependency(message: impl Into<String>) -> Response {
+pub fn failed_dependency(code: impl Into<String>, message: impl Into<String>) -> Response {
-    create_error(
+    create_error(StatusCode::FAILED_DEPENDENCY, code, message)
-        StatusCode::FAILED_DEPENDENCY,
-        "external_connector_error",
-        message,
-    )
 }
 
-pub fn not_implemented(message: impl Into<String>) -> Response {
+pub fn not_implemented(code: impl Into<String>, message: impl Into<String>) -> Response {
-    create_error(
+    create_error(StatusCode::NOT_IMPLEMENTED, code, message)
-        StatusCode::NOT_IMPLEMENTED,
-        "not_implemented_error",
-        message,
-    )
 }
 
-fn create_error(status_code: StatusCode, error_type: &str, message: impl Into<String>) -> Response {
+fn create_error(
-    let msg = message.into();
+    status: StatusCode,
+    code: impl Into<String>,
+    message: impl Into<String>,
+) -> Response {
     (
-        status_code,
+        status,
         Json(json!({
             "error": {
-                "message": msg,
+                "message": message.into(),
-                "type": error_type,
+                "type": status_code_to_str(status),
-                "code": status_code.as_u16()
+                "code": code.into(),
             }
         })),
     )
         .into_response()
 }
 
+fn status_code_to_str(status_code: StatusCode) -> &'static str {
+    match status_code {
+        // 1xx
+        StatusCode::CONTINUE => "continue",
+        StatusCode::SWITCHING_PROTOCOLS => "switching_protocols",
+        StatusCode::PROCESSING => "processing",
+        StatusCode::EARLY_HINTS => "early_hints",
+
+        // 2xx
+        StatusCode::OK => "ok",
+        StatusCode::CREATED => "created",
+        StatusCode::ACCEPTED => "accepted",
+        StatusCode::NON_AUTHORITATIVE_INFORMATION => "non_authoritative_information",
+        StatusCode::NO_CONTENT => "no_content",
+        StatusCode::RESET_CONTENT => "reset_content",
+        StatusCode::PARTIAL_CONTENT => "partial_content",
+        StatusCode::MULTI_STATUS => "multi_status",
+        StatusCode::ALREADY_REPORTED => "already_reported",
+        StatusCode::IM_USED => "im_used",
+
+        // 3xx
+        StatusCode::MULTIPLE_CHOICES => "multiple_choices",
+        StatusCode::MOVED_PERMANENTLY => "moved_permanently",
+        StatusCode::FOUND => "found",
+        StatusCode::SEE_OTHER => "see_other",
+        StatusCode::NOT_MODIFIED => "not_modified",
+        StatusCode::USE_PROXY => "use_proxy",
+        StatusCode::TEMPORARY_REDIRECT => "temporary_redirect",
+        StatusCode::PERMANENT_REDIRECT => "permanent_redirect",
+
+        // 4xx
+        StatusCode::BAD_REQUEST => "bad_request",
+        StatusCode::UNAUTHORIZED => "unauthorized",
+        StatusCode::PAYMENT_REQUIRED => "payment_required",
+        StatusCode::FORBIDDEN => "forbidden",
+        StatusCode::NOT_FOUND => "not_found",
+        StatusCode::METHOD_NOT_ALLOWED => "method_not_allowed",
+        StatusCode::NOT_ACCEPTABLE => "not_acceptable",
+        StatusCode::PROXY_AUTHENTICATION_REQUIRED => "proxy_authentication_required",
+        StatusCode::REQUEST_TIMEOUT => "request_timeout",
+        StatusCode::CONFLICT => "conflict",
+        StatusCode::GONE => "gone",
+        StatusCode::LENGTH_REQUIRED => "length_required",
+        StatusCode::PRECONDITION_FAILED => "precondition_failed",
+        StatusCode::PAYLOAD_TOO_LARGE => "payload_too_large",
+        StatusCode::URI_TOO_LONG => "uri_too_long",
+        StatusCode::UNSUPPORTED_MEDIA_TYPE => "unsupported_media_type",
+        StatusCode::RANGE_NOT_SATISFIABLE => "range_not_satisfiable",
+        StatusCode::EXPECTATION_FAILED => "expectation_failed",
+        StatusCode::IM_A_TEAPOT => "im_a_teapot",
+        StatusCode::MISDIRECTED_REQUEST => "misdirected_request",
+        StatusCode::UNPROCESSABLE_ENTITY => "unprocessable_entity",
+        StatusCode::LOCKED => "locked",
+        StatusCode::FAILED_DEPENDENCY => "failed_dependency",
+        StatusCode::UPGRADE_REQUIRED => "upgrade_required",
+        StatusCode::PRECONDITION_REQUIRED => "precondition_required",
+        StatusCode::TOO_MANY_REQUESTS => "too_many_requests",
+        StatusCode::REQUEST_HEADER_FIELDS_TOO_LARGE => "request_header_fields_too_large",
+        StatusCode::UNAVAILABLE_FOR_LEGAL_REASONS => "unavailable_for_legal_reasons",
+
+        // 5xx
+        StatusCode::INTERNAL_SERVER_ERROR => "internal_server_error",
+        StatusCode::NOT_IMPLEMENTED => "not_implemented",
+        StatusCode::BAD_GATEWAY => "bad_gateway",
+        StatusCode::SERVICE_UNAVAILABLE => "service_unavailable",
+        StatusCode::GATEWAY_TIMEOUT => "gateway_timeout",
+        StatusCode::HTTP_VERSION_NOT_SUPPORTED => "http_version_not_supported",
+        StatusCode::VARIANT_ALSO_NEGOTIATES => "variant_also_negotiates",
+        StatusCode::INSUFFICIENT_STORAGE => "insufficient_storage",
+        StatusCode::LOOP_DETECTED => "loop_detected",
+        StatusCode::NOT_EXTENDED => "not_extended",
+        StatusCode::NETWORK_AUTHENTICATION_REQUIRED => "network_authentication_required",
+
+        _ => "unknown_status_code",
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;
 
     #[test]
     fn test_internal_error_string() {
-        let response = internal_error("Test error");
+        let response = internal_error("test_error", "Test error");
         assert_eq!(response.status(), StatusCode::INTERNAL_SERVER_ERROR);
     }
 
     #[test]
     fn test_internal_error_format() {
-        let response = internal_error(format!("Error: {}", 42));
+        let response = internal_error("test_error", format!("Error: {}", 42));
         assert_eq!(response.status(), StatusCode::INTERNAL_SERVER_ERROR);
     }
 
     #[test]
     fn test_bad_request() {
-        let response = bad_request("Invalid input");
+        let response = bad_request("invalid_input", "Invalid input");
         assert_eq!(response.status(), StatusCode::BAD_REQUEST);
     }
 
     #[test]
     fn test_not_found() {
-        let response = not_found("Resource not found");
+        let response = not_found("resource_not_found", "Resource not found");
         assert_eq!(response.status(), StatusCode::NOT_FOUND);
     }
 
     #[test]
     fn test_service_unavailable() {
-        let response = service_unavailable("No workers");
+        let response = service_unavailable("no_workers", "No workers");
         assert_eq!(response.status(), StatusCode::SERVICE_UNAVAILABLE);
     }
 }

sgl-model-gateway/src/routers/grpc/common/response_collection.rs

@@ -58,7 +58,10 @@ pub async fn collect_responses(
     };
 
     if all_responses.is_empty() {
-        return Err(error::internal_error("No responses from server"));
+        return Err(error::internal_error(
+            "no_responses_from_server",
+            "No responses from server",
+        ));
     }
 
     Ok(all_responses)

sgl-model-gateway/src/routers/grpc/common/responses/utils.rs

@@ -49,6 +49,7 @@ pub async fn ensure_mcp_connection(
                     "Failed to connect to MCP server"
                 );
                 return Err(error::failed_dependency(
+                    "connect_mcp_server_failed",
                     "Failed to connect to MCP server. Check server_url and authorization.",
                 ));
             }

sgl-model-gateway/src/routers/grpc/common/stages/client_acquisition.rs

@@ -24,7 +24,10 @@ impl PipelineStage for ClientAcquisitionStage {
                 function = "ClientAcquisitionStage::execute",
                 "Worker selection stage not completed"
             );
-            error::internal_error("Worker selection not completed")
+            error::internal_error(
+                "worker_selection_not_completed",
+                "Worker selection not completed",
+            )
         })?;
 
         let clients = match workers {
@@ -43,6 +46,7 @@ impl PipelineStage for ClientAcquisitionStage {
                         "vLLM backend does not support dual (PD disaggregated) mode"
                     );
                     return Err(error::bad_request(
+                        "vllm_pd_mode_not_supported",
                         "vLLM backend does not support prefill/decode disaggregated mode. \
                          Please use runtime_type: sglang for PD mode, or use a regular (non-PD) worker configuration."
                     ));

sgl-model-gateway/src/routers/grpc/common/stages/dispatch_metadata.rs

@@ -23,7 +23,7 @@ impl PipelineStage for DispatchMetadataStage {
                 function = "DispatchMetadataStage::execute",
                 "Proto request not built"
             );
-            error::internal_error("Proto request not built")
+            error::internal_error("proto_request_not_built", "Proto request not built")
         })?;
 
         let request_id = proto_request.request_id().to_string();

sgl-model-gateway/src/routers/grpc/common/stages/request_execution.rs

@@ -42,7 +42,7 @@ impl PipelineStage for RequestExecutionStage {
                 function = "RequestExecutionStage::execute",
                 "Proto request not built"
             );
-            error::internal_error("Proto request not built")
+            error::internal_error("proto_request_not_built", "Proto request not built")
         })?;
 
         let clients = ctx.state.clients.as_mut().ok_or_else(|| {
@@ -50,7 +50,10 @@ impl PipelineStage for RequestExecutionStage {
                 function = "RequestExecutionStage::execute",
                 "Client acquisition not completed"
             );
-            error::internal_error("Client acquisition not completed")
+            error::internal_error(
+                "client_acquisition_not_completed",
+                "Client acquisition not completed",
+            )
         })?;
 
         // Extract dispatch metadata for tracing span
@@ -108,7 +111,10 @@ impl RequestExecutionStage {
                 function = "execute_single",
                 "Expected single client but got dual"
             );
-            error::internal_error("Expected single client but got dual")
+            error::internal_error(
+                "expected_single_client_got_dual",
+                "Expected single client but got dual",
+            )
         })?;
 
         let stream = client.generate(proto_request).await.map_err(|e| {
@@ -117,7 +123,10 @@ impl RequestExecutionStage {
                 error = %e,
                 "Failed to start generation"
             );
-            error::internal_error(format!("Failed to start generation: {}", e))
+            error::internal_error(
+                "start_generation_failed",
+                format!("Failed to start generation: {}", e),
+            )
         })?;
 
         Ok(ExecutionResult::Single { stream })
@@ -133,7 +142,10 @@ impl RequestExecutionStage {
                 function = "execute_dual_dispatch",
                 "Expected dual clients but got single"
             );
-            error::internal_error("Expected dual clients but got single")
+            error::internal_error(
+                "expected_dual_clients_got_single",
+                "Expected dual clients but got single",
+            )
         })?;
 
         let prefill_request = proto_request.clone_inner();
@@ -153,10 +165,10 @@ impl RequestExecutionStage {
                     error = %e,
                     "Prefill worker failed to start"
                 );
-                return Err(error::internal_error(format!(
+                return Err(error::internal_error(
-                    "Prefill worker failed to start: {}",
+                    "prefill_worker_failed_to_start",
-                    e
+                    format!("Prefill worker failed to start: {}", e),
-                )));
+                ));
             }
         };
 
@@ -169,10 +181,10 @@ impl RequestExecutionStage {
                     error = %e,
                     "Decode worker failed to start"
                 );
-                return Err(error::internal_error(format!(
+                return Err(error::internal_error(
-                    "Decode worker failed to start: {}",
+                    "decode_worker_failed_to_start",
-                    e
+                    format!("Decode worker failed to start: {}", e),
-                )));
+                ));
             }
         };
 

sgl-model-gateway/src/routers/grpc/common/stages/worker_selection.rs

@@ -52,7 +52,10 @@ impl PipelineStage for WorkerSelectionStage {
                 function = "WorkerSelectionStage::execute",
                 "Preparation stage not completed"
             );
-            error::internal_error("Preparation stage not completed")
+            error::internal_error(
+                "preparation_stage_not_completed",
+                "Preparation stage not completed",
+            )
         })?;
 
         // For Harmony, use selection_text produced during Harmony encoding
@@ -74,10 +77,10 @@ impl PipelineStage for WorkerSelectionStage {
                             model_id = ?ctx.input.model_id,
                             "No available workers for model"
                         );
-                        return Err(error::service_unavailable(format!(
+                        return Err(error::service_unavailable(
-                            "No available workers for model: {:?}",
+                            "no_available_workers",
-                            ctx.input.model_id
+                            format!("No available workers for model: {:?}", ctx.input.model_id),
-                        )));
+                        ));
                     }
                 }
             }
@@ -91,10 +94,13 @@ impl PipelineStage for WorkerSelectionStage {
                             model_id = ?ctx.input.model_id,
                             "No available PD worker pairs for model"
                         );
-                        return Err(error::service_unavailable(format!(
+                        return Err(error::service_unavailable(
-                            "No available PD worker pairs for model: {:?}",
+                            "no_available_pd_worker_pairs",
-                            ctx.input.model_id
+                            format!(
-                        )));
+                                "No available PD worker pairs for model: {:?}",
+                                ctx.input.model_id
+                            ),
+                        ));
                     }
                 }
             }

sgl-model-gateway/src/routers/grpc/harmony/processor.rs

@@ -47,7 +47,10 @@ impl HarmonyResponseProcessor {
         // Collect all completed responses (one per choice)
         let all_responses = response_collection::collect_responses(execution_result, false).await?;
         if all_responses.is_empty() {
-            return Err(error::internal_error("No responses from server"));
+            return Err(error::internal_error(
+                "no_responses_from_server",
+                "No responses from server",
+            ));
         }
 
         // Build choices by parsing output with HarmonyParserAdapter
@@ -72,7 +75,10 @@ impl HarmonyResponseProcessor {
                     error = %e,
                     "Failed to create Harmony parser"
                 );
-                error::internal_error(format!("Failed to create Harmony parser: {}", e))
+                error::internal_error(
+                    "create_harmony_parser_failed",
+                    format!("Failed to create Harmony parser: {}", e),
+                )
             })?;
 
             // Parse Harmony channels with finish_reason and matched_stop
@@ -88,7 +94,10 @@ impl HarmonyResponseProcessor {
                         error = %e,
                         "Harmony parsing failed on complete response"
                     );
-                    error::internal_error(format!("Harmony parsing failed: {}", e))
+                    error::internal_error(
+                        "harmony_parsing_failed",
+                        format!("Harmony parsing failed: {}", e),
+                    )
                 })?;
 
             // Build response message (assistant)
@@ -187,13 +196,16 @@ impl HarmonyResponseProcessor {
         // Collect all completed responses
         let all_responses = response_collection::collect_responses(execution_result, false).await?;
         if all_responses.is_empty() {
-            return Err(error::internal_error("No responses from server"));
+            return Err(error::internal_error(
+                "no_responses_from_server",
+                "No responses from server",
+            ));
         }
 
         // For Responses API, we only process the first response (n=1)
         let complete = all_responses
             .first()
-            .ok_or_else(|| error::internal_error("No complete response"))?;
+            .ok_or_else(|| error::internal_error("no_complete_response", "No complete response"))?;
 
         // Parse Harmony channels
         let mut parser = HarmonyParserAdapter::new().map_err(|e| {
@@ -202,7 +214,10 @@ impl HarmonyResponseProcessor {
                 error = %e,
                 "Failed to create Harmony parser"
             );
-            error::internal_error(format!("Failed to create Harmony parser: {}", e))
+            error::internal_error(
+                "create_harmony_parser_failed",
+                format!("Failed to create Harmony parser: {}", e),
+            )
         })?;
 
         // Convert matched_stop from proto to JSON
@@ -227,7 +242,10 @@ impl HarmonyResponseProcessor {
                     error = %e,
                     "Harmony parsing failed on complete response"
                 );
-                error::internal_error(format!("Harmony parsing failed: {}", e))
+                error::internal_error(
+                    "harmony_parsing_failed",
+                    format!("Harmony parsing failed: {}", e),
+                )
             })?;
 
         // VALIDATION: Check if model incorrectly generated Tool role messages

sgl-model-gateway/src/routers/grpc/harmony/responses.rs

@@ -332,10 +332,10 @@ async fn execute_with_mcp_loop(
                 max_iterations = MAX_TOOL_ITERATIONS,
                 "Maximum tool iterations exceeded"
             );
-            return Err(error::internal_error(format!(
+            return Err(error::internal_error(
-                "Maximum tool iterations ({}) exceeded",
+                "tool_iterations_exceeded",
-                MAX_TOOL_ITERATIONS
+                format!("Maximum tool iterations ({}) exceeded", MAX_TOOL_ITERATIONS),
-            )));
+            ));
         }
 
         debug!(
@@ -1176,10 +1176,13 @@ async fn execute_mcp_tools(
                 error = %e,
                 "Failed to parse tool arguments JSON"
             );
-            error::internal_error(format!(
+            error::internal_error(
-                "Invalid tool arguments JSON for tool '{}': {}",
+                "invalid_tool_args",
-                tool_call.function.name, e
+                format!(
-            ))
+                    "Invalid tool arguments JSON for tool '{}': {}",
+                    tool_call.function.name, e
+                ),
+            )
         })?;
 
         // Execute tool via MCP manager
@@ -1544,10 +1547,13 @@ async fn load_previous_messages(
                 error = %e,
                 "Failed to load previous response chain from storage"
             );
-            error::internal_error(format!(
+            error::internal_error(
-                "Failed to load previous response chain for {}: {}",
+                "load_previous_response_chain_failed",
-                prev_id_str, e
+                format!(
-            ))
+                    "Failed to load previous response chain for {}: {}",
+                    prev_id_str, e
+                ),
+            )
         })?;
 
     // Build conversation history from stored responses

sgl-model-gateway/src/routers/grpc/harmony/stages/preparation.rs

@@ -65,6 +65,7 @@ impl PipelineStage for HarmonyPreparationStage {
                 "Unsupported request type for Harmony pipeline"
             );
             return Err(error::bad_request(
+                "harmony_request_type_invalid",
                 "Only Chat and Responses requests supported in Harmony pipeline".to_string(),
             ));
         }
@@ -91,6 +92,7 @@ impl HarmonyPreparationStage {
                 "logprobs requested but not supported for Harmony models"
             );
             return Err(error::bad_request(
+                "harmony_logprobs_not_supported",
                 "logprobs are not supported for Harmony models".to_string(),
             ));
         }
@@ -112,7 +114,10 @@ impl HarmonyPreparationStage {
                 error = %e,
                 "Harmony build failed for chat request"
             );
-            error::bad_request(format!("Harmony build failed: {}", e))
+            error::bad_request(
+                "harmony_build_failed",
+                format!("Harmony build failed: {}", e),
+            )
         })?;
 
         // Step 4: Store results
@@ -175,6 +180,7 @@ impl HarmonyPreparationStage {
                 "Conflicting constraints: both tool_choice and text format specified"
             );
             return Err(error::bad_request(
+                "conflicting_constraints",
                 "Cannot use both tool_choice (required/function) and text format (json_object/json_schema) simultaneously".to_string(),
             ));
         }
@@ -188,7 +194,10 @@ impl HarmonyPreparationStage {
                 error = %e,
                 "Harmony build failed for responses request"
             );
-            error::bad_request(format!("Harmony build failed: {}", e))
+            error::bad_request(
+                "harmony_build_failed",
+                format!("Harmony build failed: {}", e),
+            )
         })?;
 
         // Step 4: Store results with constraint
@@ -230,7 +239,7 @@ impl HarmonyPreparationStage {
                             error = %e,
                             "Failed to build text format structural tag for JsonObject"
                         );
-                        Box::new(error::internal_error(e))
+                        Box::new(error::internal_error("build_text_format_tag_failed", e))
                     })?;
                 Ok(Some(("structural_tag".to_string(), tag)))
             }
@@ -241,7 +250,7 @@ impl HarmonyPreparationStage {
                         error = %e,
                         "Failed to build text format structural tag for JsonSchema"
                     );
-                    Box::new(error::internal_error(e))
+                    Box::new(error::internal_error("build_text_format_tag_failed", e))
                 })?;
                 Ok(Some(("structural_tag".to_string(), tag)))
             }
@@ -310,10 +319,10 @@ impl HarmonyPreparationStage {
                     tool_name = %tool_name,
                     "Specified tool not found in tools list"
                 );
-                return Err(Box::new(error::bad_request(format!(
+                return Err(Box::new(error::bad_request(
-                    "Tool '{}' not found in tools list",
+                    "tool_not_found",
-                    tool_name
+                    format!("Tool '{}' not found in tools list", tool_name),
-                ))));
+                )));
             }
             _ => {}
         }
@@ -362,10 +371,10 @@ impl HarmonyPreparationStage {
                 error = %e,
                 "Failed to serialize structural tag"
             );
-            Box::new(error::internal_error(format!(
+            Box::new(error::internal_error(
-                "Failed to serialize structural tag: {}",
+                "serialize_structural_tag_failed",
-                e
+                format!("Failed to serialize structural tag: {}", e),
-            )))
+            ))
         })
     }
 }

sgl-model-gateway/src/routers/grpc/harmony/stages/request_building.rs

@@ -38,7 +38,7 @@ impl PipelineStage for HarmonyRequestBuildingStage {
                 function = "HarmonyRequestBuildingStage::execute",
                 "Preparation stage not completed"
             );
-            error::internal_error("Preparation not completed")
+            error::internal_error("preparation_not_completed", "Preparation not completed")
         })?;
 
         // Get clients
@@ -47,7 +47,10 @@ impl PipelineStage for HarmonyRequestBuildingStage {
                 function = "HarmonyRequestBuildingStage::execute",
                 "Client acquisition stage not completed"
             );
-            error::internal_error("Client acquisition not completed")
+            error::internal_error(
+                "client_acquisition_not_completed",
+                "Client acquisition not completed",
+            )
         })?;
         let builder_client = match clients {
             ClientSelection::Single { client } => client,
@@ -57,6 +60,7 @@ impl PipelineStage for HarmonyRequestBuildingStage {
         // Harmony model support not yet implemented for vLLM
         if builder_client.is_vllm() {
             return Err(error::not_implemented(
+                "harmony_vllm_not_supported",
                 "Harmony model support is not yet implemented for vLLM backend. \
                  Please use runtime_type: sglang for Harmony models.",
             ));
@@ -72,6 +76,7 @@ impl PipelineStage for HarmonyRequestBuildingStage {
                     "Generate request type not supported for Harmony models"
                 );
                 return Err(error::bad_request(
+                    "harmony_generate_not_supported",
                     "Generate requests are not supported with Harmony models".to_string(),
                 ));
             }
@@ -102,7 +107,10 @@ impl PipelineStage for HarmonyRequestBuildingStage {
                             error = %e,
                             "Failed to build generate request from chat"
                         );
-                        error::bad_request(format!("Invalid request parameters: {}", e))
+                        error::bad_request(
+                            "invalid_request_parameters",
+                            format!("Invalid request parameters: {}", e),
+                        )
                     })?
             }
             RequestType::Responses(request) => sglang_client
@@ -120,7 +128,10 @@ impl PipelineStage for HarmonyRequestBuildingStage {
                         error = %e,
                         "Failed to build generate request from responses"
                     );
-                    error::bad_request(format!("Invalid request parameters: {}", e))
+                    error::bad_request(
+                        "invalid_request_parameters",
+                        format!("Invalid request parameters: {}", e),
+                    )
                 })?,
             _ => unreachable!(),
         };

sgl-model-gateway/src/routers/grpc/harmony/stages/response_processing.rs

@@ -56,7 +56,7 @@ impl PipelineStage for HarmonyResponseProcessingStage {
                             request_type = "Chat",
                             "No execution result available"
                         );
-                        error::internal_error("No execution result")
+                        error::internal_error("no_execution_result", "No execution result")
                     })?;
 
                 let dispatch = ctx.state.dispatch.as_ref().cloned().ok_or_else(|| {
@@ -65,7 +65,7 @@ impl PipelineStage for HarmonyResponseProcessingStage {
                         request_type = "Chat",
                         "Dispatch metadata not set"
                     );
-                    error::internal_error("Dispatch metadata not set")
+                    error::internal_error("dispatch_metadata_not_set", "Dispatch metadata not set")
                 })?;
 
                 // For streaming, delegate to streaming processor and return SSE response
@@ -107,7 +107,7 @@ impl PipelineStage for HarmonyResponseProcessingStage {
                             request_type = "Responses",
                             "No execution result available"
                         );
-                        error::internal_error("No execution result")
+                        error::internal_error("no_execution_result", "No execution result")
                     })?;
 
                 let dispatch = ctx.state.dispatch.as_ref().cloned().ok_or_else(|| {
@@ -116,7 +116,7 @@ impl PipelineStage for HarmonyResponseProcessingStage {
                         request_type = "Responses",
                         "Dispatch metadata not set"
                     );
-                    error::internal_error("Dispatch metadata not set")
+                    error::internal_error("dispatch_metadata_not_set", "Dispatch metadata not set")
                 })?;
 
                 let responses_request = ctx.responses_request_arc();
@@ -134,6 +134,7 @@ impl PipelineStage for HarmonyResponseProcessingStage {
                     "Generate request type not supported in Harmony pipeline"
                 );
                 Err(error::internal_error(
+                    "generate_requests_not_supported_in_harmony",
                     "Generate requests not supported in Harmony pipeline",
                 ))
             }

sgl-model-gateway/src/routers/grpc/pipeline.rs

@@ -224,14 +224,14 @@ impl RequestPipeline {
                     function = "execute_chat",
                     "Wrong response type: expected Chat, got Generate"
                 );
-                error::internal_error("Internal error: wrong response type")
+                error::internal_error("wrong_response_type", "Internal error: wrong response type")
             }
             None => {
                 error!(
                     function = "execute_chat",
                     "No response produced by pipeline"
                 );
-                error::internal_error("No response produced")
+                error::internal_error("no_response_produced", "No response produced")
             }
         }
     }
@@ -275,14 +275,14 @@ impl RequestPipeline {
                     function = "execute_generate",
                     "Wrong response type: expected Generate, got Chat"
                 );
-                error::internal_error("Internal error: wrong response type")
+                error::internal_error("wrong_response_type", "Internal error: wrong response type")
             }
             None => {
                 error!(
                     function = "execute_generate",
                     "No response produced by pipeline"
                 );
-                error::internal_error("No response produced")
+                error::internal_error("no_response_produced", "No response produced")
             }
         }
     }
@@ -311,6 +311,7 @@ impl RequestPipeline {
                         "Streaming attempted in responses context"
                     );
                     return Err(error::bad_request(
+                        "streaming_not_supported",
                         "Streaming is not supported in this context".to_string(),
                     ));
                 }
@@ -337,14 +338,20 @@ impl RequestPipeline {
                     function = "execute_chat_for_responses",
                     "Wrong response type: expected Chat, got Generate"
                 );
-                Err(error::internal_error("Internal error: wrong response type"))
+                Err(error::internal_error(
+                    "wrong_response_type",
+                    "Internal error: wrong response type",
+                ))
             }
             None => {
                 error!(
                     function = "execute_chat_for_responses",
                     "No response produced by pipeline"
                 );
-                Err(error::internal_error("No response produced"))
+                Err(error::internal_error(
+                    "no_response_produced",
+                    "No response produced",
+                ))
             }
         }
     }
@@ -415,7 +422,10 @@ impl RequestPipeline {
                     function = "execute_harmony_responses",
                     "No ResponsesIterationResult produced by pipeline"
                 );
-                error::internal_error("No ResponsesIterationResult produced by pipeline")
+                error::internal_error(
+                    "no_responses_iteration_result",
+                    "No ResponsesIterationResult produced by pipeline",
+                )
             })
     }
 
@@ -465,7 +475,10 @@ impl RequestPipeline {
                 function = "execute_harmony_responses_streaming",
                 "No ExecutionResult produced by pipeline"
             );
-            error::internal_error("No ExecutionResult produced by pipeline")
+            error::internal_error(
+                "no_execution_result_produced",
+                "No ExecutionResult produced by pipeline",
+            )
         })
     }
 }

sgl-model-gateway/src/routers/grpc/regular/processor.rs

@@ -278,10 +278,10 @@ impl ResponseProcessor {
             {
                 Ok(choice) => choices.push(choice),
                 Err(e) => {
-                    return Err(error::internal_error(format!(
+                    return Err(error::internal_error(
-                        "Failed to process choice {}: {}",
+                        "process_choice_failed",
-                        index, e
+                        format!("Failed to process choice {}: {}", index, e),
-                    )));
+                    ));
                 }
             }
         }
@@ -380,10 +380,10 @@ impl ResponseProcessor {
             let outputs = match stop_decoder.process_tokens(complete.output_ids()) {
                 Ok(outputs) => outputs,
                 Err(e) => {
-                    return Err(error::internal_error(format!(
+                    return Err(error::internal_error(
-                        "Failed to process tokens: {}",
+                        "process_tokens_failed",
-                        e
+                        format!("Failed to process tokens: {}", e),
-                    )))
+                    ))
                 }
             };
 

sgl-model-gateway/src/routers/grpc/regular/responses/handlers.rs

@@ -607,7 +607,10 @@ async fn execute_without_mcp(
             error = %e,
             "Failed to convert ResponsesRequest to ChatCompletionRequest"
         );
-        error::bad_request(format!("Failed to convert request: {}", e))
+        error::bad_request(
+            "convert_request_failed",
+            format!("Failed to convert request: {}", e),
+        )
     })?;
 
     // Execute chat pipeline (errors already have proper HTTP status codes)
@@ -628,7 +631,10 @@ async fn execute_without_mcp(
             error = %e,
             "Failed to convert ChatCompletionResponse to ResponsesResponse"
         );
-        error::internal_error(format!("Failed to convert to responses format: {}", e))
+        error::internal_error(
+            "convert_to_responses_format_failed",
+            format!("Failed to convert to responses format: {}", e),
+        )
     })
 }
 
@@ -713,14 +719,20 @@ async fn load_conversation_history(
                     error = %e,
                     "Failed to check conversation existence in storage"
                 );
-                error::internal_error(format!("Failed to check conversation: {}", e))
+                error::internal_error(
+                    "check_conversation_failed",
+                    format!("Failed to check conversation: {}", e),
+                )
             })?;
 
         if conversation.is_none() {
-            return Err(error::not_found(format!(
+            return Err(error::not_found(
-                "Conversation '{}' not found. Please create the conversation first using the conversations API.",
+                "conversation_not_found",
-                conv_id_str
+                format!(
-            )));
+                    "Conversation '{}' not found. Please create the conversation first using the conversations API.",
+                    conv_id_str
+                )
+            ));
         }
 
         // Load conversation history

sgl-model-gateway/src/routers/grpc/regular/responses/tool_loop.rs

@@ -257,7 +257,10 @@ pub(super) async fn execute_tool_loop(
                 error = %e,
                 "Failed to convert ResponsesRequest to ChatCompletionRequest in tool loop"
             );
-            error::bad_request(format!("Failed to convert request: {}", e))
+            error::bad_request(
+                "convert_request_failed",
+                format!("Failed to convert request: {}", e),
+            )
         })?;
 
         // Prepare tools and tool_choice for this iteration
@@ -315,7 +318,10 @@ pub(super) async fn execute_tool_loop(
                         context = "function_tool_calls",
                         "Failed to convert ChatCompletionResponse to ResponsesResponse"
                     );
-                    error::internal_error(format!("Failed to convert to responses format: {}", e))
+                    error::internal_error(
+                        "convert_to_responses_format_failed",
+                        format!("Failed to convert to responses format: {}", e),
+                    )
                 })?;
 
                 // Return response with function tool calls to caller
@@ -352,7 +358,10 @@ pub(super) async fn execute_tool_loop(
                         context = "max_tool_calls_limit",
                         "Failed to convert ChatCompletionResponse to ResponsesResponse"
                     );
-                    error::internal_error(format!("Failed to convert to responses format: {}", e))
+                    error::internal_error(
+                        "convert_to_responses_format_failed",
+                        format!("Failed to convert to responses format: {}", e),
+                    )
                 })?;
 
                 // Mark as completed but with incomplete details
@@ -481,7 +490,10 @@ pub(super) async fn execute_tool_loop(
                     context = "final_response",
                     "Failed to convert ChatCompletionResponse to ResponsesResponse"
                 );
-                error::internal_error(format!("Failed to convert to responses format: {}", e))
+                error::internal_error(
+                    "convert_to_responses_format_failed",
+                    format!("Failed to convert to responses format: {}", e),
+                )
             })?;
 
             // Inject MCP metadata into output

sgl-model-gateway/src/routers/grpc/regular/stages/chat/preparation.rs

@@ -54,7 +54,7 @@ impl ChatPreparationStage {
             Ok(msgs) => msgs,
             Err(e) => {
                 error!(function = "ChatPreparationStage::execute", error = %e, "Failed to process chat messages");
-                return Err(error::bad_request(e));
+                return Err(error::bad_request("process_messages_failed", e));
             }
         };
 
@@ -63,7 +63,10 @@ impl ChatPreparationStage {
             Ok(encoding) => encoding,
             Err(e) => {
                 error!(function = "ChatPreparationStage::execute", error = %e, "Tokenization failed");
-                return Err(error::internal_error(format!("Tokenization failed: {}", e)));
+                return Err(error::internal_error(
+                    "tokenization_failed",
+                    format!("Tokenization failed: {}", e),
+                ));
             }
         };
 
@@ -74,7 +77,7 @@ impl ChatPreparationStage {
             utils::generate_tool_constraints(tools, &request.tool_choice, &request.model)
                 .map_err(|e| {
                     error!(function = "ChatPreparationStage::execute", error = %e, "Invalid tool configuration");
-                    error::bad_request(format!("Invalid tool configuration: {}", e))
+                    error::bad_request("invalid_tool_configuration", format!("Invalid tool configuration: {}", e))
                 })?
         } else {
             None

sgl-model-gateway/src/routers/grpc/regular/stages/chat/request_building.rs

@@ -36,7 +36,7 @@ impl PipelineStage for ChatRequestBuildingStage {
                 function = "ChatRequestBuildingStage::execute",
                 "Preparation not completed"
             );
-            error::internal_error("Preparation not completed")
+            error::internal_error("preparation_not_completed", "Preparation not completed")
         })?;
 
         let clients = ctx.state.clients.as_ref().ok_or_else(|| {
@@ -44,7 +44,10 @@ impl PipelineStage for ChatRequestBuildingStage {
                 function = "ChatRequestBuildingStage::execute",
                 "Client acquisition not completed"
             );
-            error::internal_error("Client acquisition not completed")
+            error::internal_error(
+                "client_acquisition_not_completed",
+                "Client acquisition not completed",
+            )
         })?;
 
         let chat_request = ctx.chat_request_arc();
@@ -77,7 +80,7 @@ impl PipelineStage for ChatRequestBuildingStage {
                     )
                     .map_err(|e| {
                         error!(function = "ChatRequestBuildingStage::execute", error = %e, "Failed to build SGLang generate request");
-                        error::bad_request(format!("Invalid request parameters: {}", e))
+                        error::bad_request("invalid_request_parameters", format!("Invalid request parameters: {}", e))
                     })?;
                 ProtoGenerateRequest::Sglang(Box::new(req))
             }
@@ -92,7 +95,7 @@ impl PipelineStage for ChatRequestBuildingStage {
                     )
                     .map_err(|e| {
                         error!(function = "ChatRequestBuildingStage::execute", error = %e, "Failed to build vLLM generate request");
-                        error::bad_request(format!("Invalid request parameters: {}", e))
+                        error::bad_request("invalid_request_parameters", format!("Invalid request parameters: {}", e))
                     })?;
                 ProtoGenerateRequest::Vllm(Box::new(req))
             }

sgl-model-gateway/src/routers/grpc/regular/stages/chat/response_processing.rs

@@ -62,7 +62,7 @@ impl ChatResponseProcessingStage {
                 function = "ChatResponseProcessingStage::execute",
                 "No execution result"
             );
-            error::internal_error("No execution result")
+            error::internal_error("no_execution_result", "No execution result")
         })?;
 
         // Get dispatch metadata (needed by both streaming and non-streaming)
@@ -75,7 +75,7 @@ impl ChatResponseProcessingStage {
                     function = "ChatResponseProcessingStage::execute",
                     "Dispatch metadata not set"
                 );
-                error::internal_error("Dispatch metadata not set")
+                error::internal_error("dispatch_metadata_not_set", "Dispatch metadata not set")
             })?
             .clone();
 
@@ -100,7 +100,10 @@ impl ChatResponseProcessingStage {
                 function = "ChatResponseProcessingStage::execute",
                 "Stop decoder not initialized"
             );
-            error::internal_error("Stop decoder not initialized")
+            error::internal_error(
+                "stop_decoder_not_initialized",
+                "Stop decoder not initialized",
+            )
         })?;
 
         let response = self

sgl-model-gateway/src/routers/grpc/regular/stages/generate/preparation.rs

@@ -49,7 +49,7 @@ impl GeneratePreparationStage {
             Ok(res) => res,
             Err(msg) => {
                 error!(function = "GeneratePreparationStage::execute", error = %msg, "Failed to resolve generate input");
-                return Err(error::bad_request(msg));
+                return Err(error::bad_request("resolve_input_failed", msg));
             }
         };
 

sgl-model-gateway/src/routers/grpc/regular/stages/generate/request_building.rs

@@ -36,7 +36,7 @@ impl PipelineStage for GenerateRequestBuildingStage {
                 function = "GenerateRequestBuildingStage::execute",
                 "Preparation not completed"
             );
-            error::internal_error("Preparation not completed")
+            error::internal_error("preparation_not_completed", "Preparation not completed")
         })?;
 
         let clients = ctx.state.clients.as_ref().ok_or_else(|| {
@@ -44,7 +44,10 @@ impl PipelineStage for GenerateRequestBuildingStage {
                 function = "GenerateRequestBuildingStage::execute",
                 "Client acquisition not completed"
             );
-            error::internal_error("Client acquisition not completed")
+            error::internal_error(
+                "client_acquisition_not_completed",
+                "Client acquisition not completed",
+            )
         })?;
 
         let generate_request = ctx.generate_request_arc();
@@ -73,7 +76,7 @@ impl PipelineStage for GenerateRequestBuildingStage {
                     )
                     .map_err(|e| {
                         error!(function = "GenerateRequestBuildingStage::execute", error = %e, "Failed to build SGLang generate request");
-                        error::bad_request(e)
+                        error::bad_request("build_request_failed", e)
                     })?;
                 ProtoGenerateRequest::Sglang(Box::new(req))
             }
@@ -87,7 +90,7 @@ impl PipelineStage for GenerateRequestBuildingStage {
                     )
                     .map_err(|e| {
                         error!(function = "GenerateRequestBuildingStage::execute", error = %e, "Failed to build vLLM generate request");
-                        error::bad_request(e)
+                        error::bad_request("build_request_failed", e)
                     })?;
                 ProtoGenerateRequest::Vllm(Box::new(req))
             }

sgl-model-gateway/src/routers/grpc/regular/stages/generate/response_processing.rs

@@ -60,7 +60,7 @@ impl GenerateResponseProcessingStage {
                 function = "GenerateResponseProcessingStage::execute",
                 "No execution result"
             );
-            error::internal_error("No execution result")
+            error::internal_error("no_execution_result", "No execution result")
         })?;
 
         // Get dispatch metadata (needed by both streaming and non-streaming)
@@ -73,7 +73,7 @@ impl GenerateResponseProcessingStage {
                     function = "GenerateResponseProcessingStage::execute",
                     "Dispatch metadata not set"
                 );
-                error::internal_error("Dispatch metadata not set")
+                error::internal_error("dispatch_metadata_not_set", "Dispatch metadata not set")
             })?
             .clone();
 
@@ -97,7 +97,10 @@ impl GenerateResponseProcessingStage {
                 function = "GenerateResponseProcessingStage::execute",
                 "Stop decoder not initialized"
             );
-            error::internal_error("Stop decoder not initialized")
+            error::internal_error(
+                "stop_decoder_not_initialized",
+                "Stop decoder not initialized",
+            )
         })?;
 
         let result_array = self

sgl-model-gateway/src/routers/grpc/regular/stages/preparation.rs

@@ -49,6 +49,7 @@ impl PipelineStage for PreparationStage {
                     "RequestType::Responses reached regular preparation stage"
                 );
                 Err(grpc_error::internal_error(
+                    "responses_in_wrong_pipeline",
                     "RequestType::Responses reached regular preparation stage",
                 ))
             }

sgl-model-gateway/src/routers/grpc/regular/stages/request_building.rs

@@ -40,6 +40,7 @@ impl PipelineStage for RequestBuildingStage {
                     "RequestType::Responses reached regular request building stage"
                 );
                 Err(grpc_error::internal_error(
+                    "responses_in_wrong_pipeline",
                     "RequestType::Responses reached regular request building stage",
                 ))
             }

sgl-model-gateway/src/routers/grpc/regular/stages/response_processing.rs

@@ -49,6 +49,7 @@ impl PipelineStage for ResponseProcessingStage {
                     "RequestType::Responses reached regular response processing stage"
                 );
                 Err(error::internal_error(
+                    "responses_in_wrong_pipeline",
                     "RequestType::Responses reached regular response processing stage",
                 ))
             }

sgl-model-gateway/src/routers/grpc/utils.rs

@@ -52,14 +52,20 @@ pub async fn get_grpc_client_from_worker(worker: &Arc<dyn Worker>) -> Result<Grp
                 error = %e,
                 "Failed to get gRPC client from worker"
             );
-            error::internal_error(format!("Failed to get gRPC client: {}", e))
+            error::internal_error(
+                "get_grpc_client_failed",
+                format!("Failed to get gRPC client: {}", e),
+            )
         })?
         .ok_or_else(|| {
             error!(
                 function = "get_grpc_client_from_worker",
                 "Selected worker not configured for gRPC"
             );
-            error::internal_error("Selected worker is not configured for gRPC")
+            error::internal_error(
+                "worker_not_configured_for_grpc",
+                "Selected worker is not configured for gRPC",
+            )
         })?;
 
     Ok((*client_arc).clone())
@@ -612,11 +618,10 @@ pub async fn collect_stream_responses(
                     ProtoResponseVariant::Error(err) => {
                         error!(function = "collect_stream_responses", worker = %worker_name, error = %err.message(), "Worker generation error");
                         // Don't mark as completed - let Drop send abort for error cases
-                        return Err(error::internal_error(format!(
+                        return Err(error::internal_error(
-                            "{} generation failed: {}",
+                            "worker_generation_failed",
-                            worker_name,
+                            format!("{} generation failed: {}", worker_name, err.message()),
-                            err.message()
+                        ));
-                        )));
                     }
                     ProtoResponseVariant::Chunk(_chunk) => {
                         // Streaming chunk - no action needed
@@ -629,10 +634,10 @@ pub async fn collect_stream_responses(
             Err(e) => {
                 error!(function = "collect_stream_responses", worker = %worker_name, error = ?e, "Worker stream error");
                 // Don't mark as completed - let Drop send abort for error cases
-                return Err(error::internal_error(format!(
+                return Err(error::internal_error(
-                    "{} stream failed: {}",
+                    "worker_stream_failed",
-                    worker_name, e
+                    format!("{} stream failed: {}", worker_name, e),
-                )));
+                ));
             }
         }
     }