[router][grpc] Refactor chat template content format detection (#11288)

sgl-router/tests/chat_template_format_detection.rs

@@ -249,3 +249,65 @@ fn test_chat_template_with_tokens_unit_test() {
     assert!(result.contains("<s>"));
     assert!(result.contains("</s>"));
 }
+
+#[test]
+fn test_detect_openai_format_qwen3vl_macro_style() {
+    // Qwen3-VL style template using macros to handle multimodal content
+    // This tests the macro-based detection pattern
+    let template = r#"{%- set image_count = namespace(value=0) %}
+{%- set video_count = namespace(value=0) %}
+{%- macro render_content(content, do_vision_count) %}
+    {%- if content is string %}
+        {{- content }}
+    {%- else %}
+        {%- for item in content %}
+            {%- if 'image' in item or 'image_url' in item or item.type == 'image' %}
+                {%- if do_vision_count %}
+                    {%- set image_count.value = image_count.value + 1 %}
+                {%- endif %}
+                {%- if add_vision_id %}Picture {{ image_count.value }}: {% endif -%}
+                <|vision_start|><|image_pad|><|vision_end|>
+            {%- elif 'video' in item or item.type == 'video' %}
+                {%- if do_vision_count %}
+                    {%- set video_count.value = video_count.value + 1 %}
+                {%- endif %}
+                {%- if add_vision_id %}Video {{ video_count.value }}: {% endif -%}
+                <|vision_start|><|video_pad|><|vision_end|>
+            {%- elif 'text' in item %}
+                {{- item.text }}
+            {%- endif %}
+        {%- endfor %}
+    {%- endif %}
+{%- endmacro %}
+{%- for message in messages %}
+    {%- set content = render_content(message.content, True) %}
+    {{- '<|im_start|>' + message.role + '\n' + content + '<|im_end|>' + '\n' }}
+{%- endfor %}
+{%- if add_generation_prompt %}
+    {{- '<|im_start|>assistant\n' }}
+{%- endif %}"#;
+
+    assert_eq!(
+        detect_chat_template_content_format(template),
+        ChatTemplateContentFormat::OpenAI
+    );
+}
+
+#[test]
+fn test_detect_openai_format_arbitrary_variable_names() {
+    // Test that detection works with any variable name, not just "message", "msg", "m"
+    // Uses "chat_msg" and "x" as loop variables
+    let template = r#"
+        {%- for chat_msg in messages %}
+        {%- for x in chat_msg.content %}
+        {%- if x.type == 'text' %}{{ x.text }}{%- endif %}
+        {%- if x.type == 'image' %}<image>{%- endif %}
+        {%- endfor %}
+        {%- endfor %}
+        "#;
+
+    assert_eq!(
+        detect_chat_template_content_format(template),
+        ChatTemplateContentFormat::OpenAI
+    );
+}