Quick vibe-coded fix for proper object printing

common/chat-diff-analyzer.cpp

@@ -192,6 +192,7 @@ std::optional<compare_variants_result> differential_analyzer::compare_variants(
     if (params_modifier) {
         params_modifier(params_B);
     }
+    
 
     // Apply template to both variants
     std::string output_A = apply_template(tmpl, params_A);
@@ -683,7 +684,8 @@ void differential_analyzer::analyze_tool_call_format_json_native(const std::stri
     // we might not have the typical OpenAI tool calling structure
     int  json_start     = clean_haystack.find_first_of('{');
     int  json_end       = clean_haystack.find_last_of('}');
-    json call_struct    = json::parse(clean_haystack.substr(json_start, json_end - json_start + 1));
+    std::string cut     = clean_haystack.substr(json_start, json_end - json_start + 1);
+    json call_struct    = json::parse(cut);
     auto register_field = [&](const std::string &                                             prefix,
                               const nlohmann::detail::iteration_proxy_value<json::iterator> & subel) {
         if (subel.value().is_string() && std::string(subel.value()).find("call0000") != std::string::npos) {

common/chat.cpp

@@ -116,7 +116,7 @@ json common_chat_msg::to_json_oaicompat(bool concat_typed_text) const {
                 {"type", "function"},
                 {"function", {
                     {"name", tool_call.name},
-                    {"arguments", tool_call.arguments},
+                    {"arguments", json::parse(tool_call.arguments)},
                 }},
             };
             if (!tool_call.id.empty()) {

common/jinja/value.h

@@ -502,12 +502,21 @@ struct value_object_t : public value_t {
     virtual bool is_immutable() const override { return false; }
     virtual const std::vector<std::pair<value, value>> & as_ordered_object() const override { return val_obj; }
     virtual string as_string() const override {
+        // Use JSON format for object string representation to ensure compatibility
+        // when concatenated in templates (e.g., '{"name": ' + arguments + '}')
         std::ostringstream ss;
         ss << "{";
         for (size_t i = 0; i < val_obj.size(); i++) {
             if (i > 0) ss << ", ";
             auto & [key, val] = val_obj.at(i);
-            ss << value_to_string_repr(key) << ": " << value_to_string_repr(val);
+            // Use double quotes for keys (JSON format)
+            ss << "\"" << key->as_string().str() << "\": ";
+            if (is_val<value_string>(val)) {
+                // Strings need to be quoted in JSON
+                ss << "\"" << val->as_string().str() << "\"";
+            } else {
+                ss << val->as_string().str();
+            }
         }
         ss << "}";
         return ss.str();

tests/test-chat.cpp

@@ -973,7 +973,6 @@ static void test_msgs_oaicompat_json_conversion() {
                   common_chat_msgs_to_json_oaicompat({ message_user_parts }).dump(2));
 
     // Note: content is "" instead of null due to workaround for templates that render null as "None"
-    // Arguments are serialized as string for OAI compatibility
     assert_equals(std::string("[\n"
                               "  {\n"
                               "    \"role\": \"assistant\",\n"
@@ -983,7 +982,9 @@ static void test_msgs_oaicompat_json_conversion() {
                               "        \"type\": \"function\",\n"
                               "        \"function\": {\n"
                               "          \"name\": \"python\",\n"
-                              "          \"arguments\": \"{\\\"code\\\":\\\"print('hey')\\\"}\"\n"
+                              "          \"arguments\": {\n"
+                              "            \"code\": \"print('hey')\"\n"
+                              "          }\n"
                               "        }\n"
                               "      }\n"
                               "    ]\n"