[router] fix chat template loading and tokenizer path (#10999)

sgl-router/src/tokenizer/factory.rs

@@ -134,6 +134,36 @@ fn is_likely_sentencepiece(buffer: &[u8]) -> bool {
             || buffer.windows(4).any(|w| w == b"</s>"))
 }
 
+/// Helper function to discover chat template files in a directory
+pub fn discover_chat_template_in_dir(dir: &Path) -> Option<String> {
+    use std::fs;
+
+    // Priority 1: Look for chat_template.json (contains Jinja in JSON format)
+    let json_template_path = dir.join("chat_template.json");
+    if json_template_path.exists() {
+        return json_template_path.to_str().map(|s| s.to_string());
+    }
+
+    // Priority 2: Look for chat_template.jinja (standard Jinja file)
+    let jinja_path = dir.join("chat_template.jinja");
+    if jinja_path.exists() {
+        return jinja_path.to_str().map(|s| s.to_string());
+    }
+
+    // Priority 3: Look for any .jinja file (for models with non-standard naming)
+    if let Ok(entries) = fs::read_dir(dir) {
+        for entry in entries.flatten() {
+            if let Some(name) = entry.file_name().to_str() {
+                if name.ends_with(".jinja") && name != "chat_template.jinja" {
+                    return entry.path().to_str().map(|s| s.to_string());
+                }
+            }
+        }
+    }
+
+    None
+}
+
 /// Factory function to create tokenizer from a model name or path (async version)
 pub async fn create_tokenizer_async(
     model_name_or_path: &str,
@@ -161,14 +191,32 @@ pub async fn create_tokenizer_async(
             // Look for tokenizer.json in the cache directory
             let tokenizer_path = cache_dir.join("tokenizer.json");
             if tokenizer_path.exists() {
-                create_tokenizer_from_file(tokenizer_path.to_str().unwrap())
+                // Try to find a chat template file in the cache directory
+                let chat_template_path = discover_chat_template_in_dir(&cache_dir);
+                let tokenizer_path_str = tokenizer_path.to_str().ok_or_else(|| {
+                    Error::msg(format!(
+                        "Tokenizer path is not valid UTF-8: {:?}",
+                        tokenizer_path
+                    ))
+                })?;
+                create_tokenizer_with_chat_template(
+                    tokenizer_path_str,
+                    chat_template_path.as_deref(),
+                )
             } else {
                 // Try other common tokenizer file names
                 let possible_files = ["tokenizer_config.json", "vocab.json"];
                 for file_name in &possible_files {
                     let file_path = cache_dir.join(file_name);
                     if file_path.exists() {
-                        return create_tokenizer_from_file(file_path.to_str().unwrap());
+                        let chat_template_path = discover_chat_template_in_dir(&cache_dir);
+                        let file_path_str = file_path.to_str().ok_or_else(|| {
+                            Error::msg(format!("File path is not valid UTF-8: {:?}", file_path))
+                        })?;
+                        return create_tokenizer_with_chat_template(
+                            file_path_str,
+                            chat_template_path.as_deref(),
+                        );
                     }
                 }
                 Err(Error::msg(format!(