[router][grpc] Consolidate parser checks for chat completions (#11439)

sgl-router/src/tool_parser/factory.rs

@@ -6,7 +6,7 @@ use tokio::sync::Mutex;
 
 use crate::tool_parser::parsers::{
     DeepSeekParser, Glm4MoeParser, GptOssHarmonyParser, GptOssParser, JsonParser, KimiK2Parser,
-    LlamaParser, MistralParser, PythonicParser, QwenParser, Step3Parser,
+    LlamaParser, MistralParser, PassthroughParser, PythonicParser, QwenParser, Step3Parser,
 };
 use crate::tool_parser::traits::ToolParser;
 
@@ -36,7 +36,7 @@ impl ParserRegistry {
             creators: Arc::new(RwLock::new(HashMap::new())),
             pool: Arc::new(RwLock::new(HashMap::new())),
             model_mapping: Arc::new(RwLock::new(HashMap::new())),
-            default_parser: Arc::new(RwLock::new("json".to_string())),
+            default_parser: Arc::new(RwLock::new("passthrough".to_string())),
         }
     }
 
@@ -124,10 +124,9 @@ impl ParserRegistry {
             }
         }
 
-        // Check if default parser exists
-        let default = self.default_parser.read().unwrap().clone();
-        let creators = self.creators.read().unwrap();
-        creators.contains_key(&default)
+        // Return false if no specific parser found for this model
+        // (get_pooled will still fall back to default parser)
+        false
     }
 
     /// Create a fresh (non-pooled) parser instance for a specific model.
@@ -228,6 +227,7 @@ impl ParserFactory {
         let registry = ParserRegistry::new();
 
         // Register default parsers
+        registry.register_parser("passthrough", || Box::new(PassthroughParser::new()));
         registry.register_parser("json", || Box::new(JsonParser::new()));
         registry.register_parser("mistral", || Box::new(MistralParser::new()));
         registry.register_parser("qwen", || Box::new(QwenParser::new()));
@@ -311,15 +311,15 @@ impl ParserFactory {
 
     /// Get a pooled parser for the given model ID.
     /// Returns a shared instance that can be used concurrently.
-    /// Falls back to JSON parser if model is not recognized.
+    /// Falls back to passthrough parser if model is not recognized.
     pub fn get_pooled(&self, model_id: &str) -> PooledParser {
         self.registry
             .get_pooled_for_model(model_id)
             .unwrap_or_else(|| {
-                // Fallback to JSON parser
+                // Fallback to passthrough parser (no-op, returns text unchanged)
                 self.registry
-                    .get_pooled_parser("json")
-                    .expect("JSON parser should always be registered")
+                    .get_pooled_parser("passthrough")
+                    .expect("Passthrough parser should always be registered")
             })
     }