From c6b9134df836b08f82d18788850b7efee5144125 Mon Sep 17 00:00:00 2001
From: Tlotli Mosalo <tlotlimosalo@gmail.com>
Date: Sat, 16 May 2026 06:23:16 +0200
Subject: [PATCH] fix(deepseek): preserve reasoning_content in thinking mode
 for tool calls

DeepSeek's thinking mode requires reasoning_content to be passed back
in all subsequent requests when tool calls are involved. Without this,
the API returns 400: 'The reasoning_content in the thinking mode must
be passed back to the API.'

Two fixes:
- Text.php: Extract reasoning_content from raw response and include
  it in AssistantMessage.additionalContent for both tool call steps
  and the final response step.
- MessageMap.php: Merge additionalContent into the API payload so
  reasoning_content is sent back to the API in multi-turn conversations.

Fixes multi-turn conversations with tools in deepseek-v4-flash.
---
 src/Providers/DeepSeek/Handlers/Text.php   | 9 +++++++--
 src/Providers/DeepSeek/Maps/MessageMap.php | 4 ++--
 2 files changed, 9 insertions(+), 4 deletions(-)

diff --git a/src/Providers/DeepSeek/Handlers/Text.php b/src/Providers/DeepSeek/Handlers/Text.php
index c8a15d253..d9cf14324 100644
--- a/src/Providers/DeepSeek/Handlers/Text.php
+++ b/src/Providers/DeepSeek/Handlers/Text.php
@@ -63,10 +63,13 @@ protected function handleToolCalls(array $data, Request $request): TextResponse
 
         $this->addStep($data, $request, $toolResults);
 
+        $reasoningContent = data_get($data, 'choices.0.message.reasoning_content');
+        $additionalContent = $reasoningContent ? ['reasoning_content' => $reasoningContent] : [];
+
         $request = $request->addMessage(new AssistantMessage(
             data_get($data, 'choices.0.message.content') ?? '',
             $toolCalls,
-            []
+            $additionalContent
         ));
         $request = $request->addMessage(new ToolResultMessage($toolResults));
         $request->resetToolChoice();
@@ -122,6 +125,8 @@ protected function sendRequest(Request $request): array
      */
     protected function addStep(array $data, Request $request, array $toolResults = []): void
     {
+        $reasoningContent = data_get($data, 'choices.0.message.reasoning_content');
+
         $this->responseBuilder->addStep(new Step(
             text: data_get($data, 'choices.0.message.content') ?? '',
             finishReason: $this->mapFinishReason($data),
@@ -138,7 +143,7 @@ protected function addStep(array $data, Request $request, array $toolResults = [
             ),
             messages: $request->messages(),
             systemPrompts: $request->systemPrompts(),
-            additionalContent: [],
+            additionalContent: $reasoningContent ? ['reasoning_content' => $reasoningContent] : [],
             raw: $data,
         ));
     }
diff --git a/src/Providers/DeepSeek/Maps/MessageMap.php b/src/Providers/DeepSeek/Maps/MessageMap.php
index c75352761..f414e498a 100644
--- a/src/Providers/DeepSeek/Maps/MessageMap.php
+++ b/src/Providers/DeepSeek/Maps/MessageMap.php
@@ -99,10 +99,10 @@ protected function mapAssistantMessage(AssistantMessage $message): void
             ],
         ], $message->toolCalls);
 
-        $this->mappedMessages[] = array_filter([
+        $this->mappedMessages[] = array_filter(array_merge([
             'role' => 'assistant',
             'content' => $message->content,
             'tool_calls' => $toolCalls,
-        ]);
+        ], $message->additionalContent));
     }
 }