Fixing the router + template for Qwen3. (#3200)

Author: Narsil

router/src/config.rs

@@ -414,6 +414,7 @@ pub enum Config {
     T5,
     DeepseekV2,
     DeepseekV3,
+    Qwen3,
 }
 
 #[derive(Clone, Debug, Serialize, Deserialize)]

router/src/infer/chat_template.rs

@@ -41,6 +41,10 @@ impl ChatTemplate {
             "messages[0]['content'][0]['text']",
             "messages[0]['content']",
         );
+        //  Hack to fix Qwen3 templating.
+        //  It uses python notation to reverse lists, which do not exist in minijinja
+        //  so we're using the reverse filter instead.
+        let mutated_template = mutated_template.replace("[::-1]", "|reverse");
 
         let template_str = mutated_template.into_boxed_str();
         env.add_function("raise_exception", raise_exception);