Revert "perf: switch to qwen-style chat template"

This reverts commit db92212697efac74c50708139d7a5e5ab7948486.

crates/inference-server/src/compat.rs

@@ -301,7 +301,9 @@ pub fn prepare_prompt(req: &ChatCompletionRequest, config: &ServerConfig) -> Pre
         .any(|message| matches!(message.role, Role::System | Role::Developer));
 
     if !has_system {
-        append_chat_message(&mut prompt, "system", None, &config.default_system_prompt);
+        prompt.push_str("System: ");
+        prompt.push_str(&config.default_system_prompt);
+        prompt.push('\n');
     }
 
     if let Some(format) = &req.response_format {
@@ -314,31 +316,37 @@ pub fn prepare_prompt(req: &ChatCompletionRequest, config: &ServerConfig) -> Pre
 
     for msg in &req.messages {
         let role = match msg.role {
-            Role::System => "system",
+            Role::System => "System",
-            Role::Developer => "system",
+            Role::Developer => "Developer",
-            Role::User => "user",
+            Role::User => "User",
-            Role::Assistant => "assistant",
+            Role::Assistant => "Assistant",
-            Role::Tool => "tool",
+            Role::Tool => "Tool",
         };
+        prompt.push_str(role);
+        if let Some(name) = &msg.name {
+            prompt.push_str("(");
+            prompt.push_str(name);
+            prompt.push(')');
+        }
+        prompt.push_str(": ");
 
-        let content = if let Some(tool_calls) = &msg.tool_calls {
+        if let Some(tool_calls) = &msg.tool_calls {
-            serde_json::to_string(tool_calls).unwrap_or_else(|_| "[]".to_owned())
+            let tool_json = serde_json::to_string(tool_calls).unwrap_or_else(|_| "[]".to_owned());
+            prompt.push_str(&tool_json);
         } else {
-            msg.text().to_owned()
+            prompt.push_str(msg.text());
-        };
+        }
 
         if let Some(tool_call_id) = &msg.tool_call_id {
-            let mut with_id = content;
+            prompt.push_str(" [tool_call_id=");
-            with_id.push_str("\n[tool_call_id=");
+            prompt.push_str(tool_call_id);
-            with_id.push_str(tool_call_id);
+            prompt.push(']');
-            with_id.push(']');
-            append_chat_message(&mut prompt, role, msg.name.as_deref(), &with_id);
-        } else {
-            append_chat_message(&mut prompt, role, msg.name.as_deref(), &content);
-        }
         }
 
-    prompt.push_str("<|im_start|>assistant\n");
+        prompt.push('\n');
+    }
+
+    prompt.push_str("Assistant:");
 
     PreparedPrompt {
         prompt,
@@ -390,20 +398,14 @@ pub fn tool_calls_to_delta(tool_calls: &[ToolCall]) -> Vec<DeltaToolCall> {
 fn append_response_format_instruction(prompt: &mut String, format: &ResponseFormat) {
     match format.format_type.as_str() {
         "json_object" => {
-            append_chat_message(
+            prompt.push_str("System: Return valid JSON only. Do not wrap it in markdown fences.\n");
-                prompt,
-                "system",
-                None,
-                "Return valid JSON only. Do not wrap it in markdown fences.",
-            );
         }
         "json_schema" => {
-            let mut instruction =
+            prompt.push_str("System: Return valid JSON only and follow this schema exactly: ");
-                "Return valid JSON only and follow this schema exactly: ".to_owned();
             if let Some(schema) = &format.json_schema {
-                instruction.push_str(&schema.to_string());
+                prompt.push_str(&schema.to_string());
             }
-            append_chat_message(prompt, "system", None, &instruction);
+            prompt.push('\n');
         }
         _ => {}
     }
@@ -425,67 +427,32 @@ fn append_tool_instructions(
         })
         .collect();
 
-    append_chat_message(
+    prompt.push_str("System: Available tools: ");
-        prompt,
+    prompt.push_str(&serde_json::to_string(&tool_summaries).unwrap_or_else(|_| "[]".to_owned()));
-        "system",
+    prompt.push('\n');
-        None,
+    prompt
-        &format!(
+        .push_str("System: If you need a tool, respond with JSON only using one of these shapes: ");
-            "Available tools: {}",
+    prompt.push_str(r#"{"tool_calls":[{"name":"tool_name","arguments":{}}]}"#);
-            serde_json::to_string(&tool_summaries).unwrap_or_else(|_| "[]".to_owned())
+    prompt.push_str(" or ");
-        ),
+    prompt.push_str(r#"{"name":"tool_name","arguments":{}}"#);
-    );
+    prompt.push_str(". If no tool is needed, answer normally.\n");
-    append_chat_message(
-        prompt,
-        "system",
-        None,
-        &format!(
-            "If you need a tool, respond with JSON only using one of these shapes: {} or {}. If no tool is needed, answer normally.",
-            r#"{"tool_calls":[{"name":"tool_name","arguments":{}}]}"#,
-            r#"{"name":"tool_name","arguments":{}}"#,
-        ),
-    );
 
     match tool_choice {
         Some(ToolChoice::Mode(mode)) if mode == "required" => {
-            append_chat_message(
+            prompt.push_str("System: You must call a tool before replying.\n");
-                prompt,
-                "system",
-                None,
-                "You must call a tool before replying.",
-            );
         }
         Some(ToolChoice::Mode(mode)) if mode == "none" => {
-            append_chat_message(
+            prompt.push_str("System: Do not call tools in this response.\n");
-                prompt,
-                "system",
-                None,
-                "Do not call tools in this response.",
-            );
         }
         Some(ToolChoice::Specific(choice)) => {
-            append_chat_message(
+            prompt.push_str("System: You must call the tool named ");
-                prompt,
+            prompt.push_str(&choice.function.name);
-                "system",
+            prompt.push_str(".\n");
-                None,
-                &format!("You must call the tool named {}.", choice.function.name),
-            );
         }
         _ => {}
     }
 }
 
-fn append_chat_message(prompt: &mut String, role: &str, name: Option<&str>, content: &str) {
-    prompt.push_str("<|im_start|>");
-    prompt.push_str(role);
-    if let Some(name) = name {
-        prompt.push(' ');
-        prompt.push_str(name);
-    }
-    prompt.push('\n');
-    prompt.push_str(content);
-    prompt.push_str("<|im_end|>\n");
-}
-
 fn parse_tool_calls(raw_output: &str) -> Option<Vec<ToolCall>> {
     let trimmed = raw_output.trim();
     if trimmed.is_empty() {
@@ -694,8 +661,6 @@ mod tests {
         assert!(prepared.prompt.contains("Default coding system prompt"));
         assert!(prepared.prompt.contains("list_files"));
         assert!(prepared.prompt.contains("must call a tool"));
-        assert!(prepared.prompt.contains("<|im_start|>system\n"));
-        assert!(prepared.prompt.ends_with("<|im_start|>assistant\n"));
     }
 
     #[test]