chat: trim messages sent to StepFun parser (fixes long reasoning loops)

common/chat.cpp

@@ -2378,6 +2378,23 @@ static void func_args_not_string(json & messages) {
     }
 }
 
+// Trim leading/trailing whitespace from message contents before rendering. This
+// has to run on the messages (not on the rendered JSON) because templates with
+// string-only content caps concatenate typed content parts into a single string
+// during rendering, after which the per-part whitespace can no longer be reached.
+// Both the plain string content and the text of typed content parts are trimmed.
+static void trim_all_content(std::vector<common_chat_msg> & messages) {
+    for (auto & message : messages) {
+        message.content           = trim_whitespace(message.content);
+        message.reasoning_content = trim_whitespace(message.reasoning_content);
+        for (auto & part : message.content_parts) {
+            if (part.type == "text") {
+                part.text = trim_whitespace(part.text);
+            }
+        }
+    }
+}
+
 }
 
 // MiniCPM5 format:
@@ -2634,7 +2651,16 @@ static common_chat_params common_chat_templates_apply_jinja(const struct common_
         params.tools.is_array() && tmpls->template_tool_use ? *tmpls->template_tool_use : *tmpls->template_default;
     const auto & src             = tmpl.source();
     const auto & caps            = tmpl.original_caps();
-    params.messages              = render_message_to_json(inputs.messages, tmpl.original_caps());
+    std::vector<common_chat_msg>        trimmed_messages;
+    const std::vector<common_chat_msg> * messages_to_render = &inputs.messages;
+    if (src.find("You have access to the following functions in JSONSchema format") != std::string::npos) {
+        // StepFun: trim message contents (including typed content parts) before rendering,
+        // otherwise leftover whitespace drives the model into reasoning loops (issue #24181)
+        trimmed_messages   = inputs.messages;
+        workaround::trim_all_content(trimmed_messages);
+        messages_to_render = &trimmed_messages;
+    }
+    params.messages              = render_message_to_json(*messages_to_render, tmpl.original_caps());
     params.tool_choice           = inputs.tool_choice;
     params.reasoning_format      = inputs.reasoning_format;
     params.enable_thinking       = inputs.enable_thinking;

tests/test-chat-auto-parser.cpp

@@ -1887,7 +1887,6 @@ static void test_role_markers_all_templates(testing & t) {
         { "Qwen-Qwen3-0.6B.jinja",                           "<|im_start|>user",       "<|im_start|>assistant"      },
         { "Qwen-QwQ-32B.jinja",                              "<|im_start|>user",       "<|im_start|>assistant"      },
         { "StepFun3.5-Flash.jinja",                          "<|im_start|>user",       "<|im_start|>assistant"      },
-        { "stepfun-ai-Step-3.5-Flash.jinja",                 "<|im_start|>user",       "<|im_start|>assistant"      },
 
         // DeepSeek family
         { "deepseek-ai-DeepSeek-R1-Distill-Llama-8B.jinja",  "<｜User｜>",                "<｜Assistant｜>"             },

tests/test-chat.cpp

@@ -3155,6 +3155,59 @@ static void test_template_output_peg_parsers(bool detailed_debug) {
                 }
             }
         }
+
+        {
+            // StepFun trimming regression test (see https://github.com/ggml-org/llama.cpp/pull/25238)
+            auto tmpls = read_templates("models/templates/StepFun3.5-Flash.jinja");
+
+            common_chat_msg message_chatbot = simple_assist_msg("Let me check.\n\n", "I am thinking.\n\n");
+
+            {
+                common_chat_templates_inputs inputs;
+                inputs.messages              = { message_chatbot };
+                inputs.add_generation_prompt = true;
+
+                auto params = common_chat_templates_apply(tmpls.get(), inputs);
+
+                if (params.prompt.find("Let me check.\n\n") != std::string::npos) {
+                    throw std::runtime_error("StepFun 3.5: content not trimmed");
+                }
+
+                if (params.prompt.find("I am thinking.\n\n") != std::string::npos) {
+                    throw std::runtime_error("StepFun 3.5: reasoning_content not trimmed");
+                }
+            }
+
+            {
+                // Trimming must also reach typed (text) content parts, not just string content
+                // (see https://github.com/ggml-org/llama.cpp/pull/25238)
+                common_chat_msg message_parts;
+                message_parts.role          = "user";
+                message_parts.content_parts = {
+                    { /* .type = */ "text", /* .text = */ "First part.\n\n" },
+                    { /* .type = */ "media_marker", /* .text = */ "<__media__>" },
+                    { /* .type = */ "text", /* .text = */ "Second part.\n\n" },
+                };
+
+                common_chat_templates_inputs inputs;
+                inputs.messages              = { message_parts };
+                inputs.add_generation_prompt = true;
+
+                auto params = common_chat_templates_apply(tmpls.get(), inputs);
+
+                if (params.prompt.find("First part.\n\n") != std::string::npos ||
+                    params.prompt.find("Second part.\n\n") != std::string::npos) {
+                    throw std::runtime_error("StepFun 3.5: text content parts not trimmed");
+                }
+
+                // the trimmed text itself must still be present
+                if (params.prompt.find("First part.") == std::string::npos ||
+                    params.prompt.find("Second part.") == std::string::npos) {
+                    throw std::runtime_error("StepFun 3.5: text content parts missing after trim");
+                }
+            }
+        }
+
     }
 
     {