feat: return reasoning_content with tool_calls for DeepSeek models (#2543)

* feat: return reasoning_content with tool_calls for DeepSeek models

* fix: correct reasoning_content handling for DeepSeek tool_calls

* test: cover DeepSeek reasoning content round trip

---------

Co-authored-by: Jason <farion1231@gmail.com>

src-tauri/src/proxy/providers/claude.rs

@@ -82,9 +82,9 @@ pub fn claude_api_format_needs_transform(api_format: &str) -> bool {
     )
 }
 
-fn is_moonshot_or_kimi_identifier(value: &str) -> bool {
+fn is_reasoning_content_compatible_identifier(value: &str) -> bool {
     let value = value.to_ascii_lowercase();
-    value.contains("moonshot") || value.contains("kimi")
+    value.contains("moonshot") || value.contains("kimi") || value.contains("deepseek")
 }
 
 fn should_preserve_reasoning_content_for_openai_chat(
@@ -94,7 +94,7 @@ fn should_preserve_reasoning_content_for_openai_chat(
     if body
         .get("model")
         .and_then(|m| m.as_str())
-        .is_some_and(is_moonshot_or_kimi_identifier)
+        .is_some_and(is_reasoning_content_compatible_identifier)
     {
         return true;
     }
@@ -113,7 +113,7 @@ fn should_preserve_reasoning_content_for_openai_chat(
     base_urls
         .into_iter()
         .flatten()
-        .any(is_moonshot_or_kimi_identifier)
+        .any(is_reasoning_content_compatible_identifier)
 }
 
 pub fn transform_claude_request_for_api_format(
@@ -1673,4 +1673,39 @@ mod tests {
         assert_eq!(msg["reasoning_content"], "I should call the tool.");
         assert!(msg.get("tool_calls").is_some());
     }
+
+    #[test]
+    fn test_transform_openai_chat_preserves_reasoning_content_for_deepseek_provider() {
+        let provider = create_provider_with_meta(
+            json!({
+                "env": {
+                    "ANTHROPIC_BASE_URL": "https://api.deepseek.com/v1",
+                    "ANTHROPIC_API_KEY": "test-key"
+                }
+            }),
+            ProviderMeta {
+                api_format: Some("openai_chat".to_string()),
+                ..Default::default()
+            },
+        );
+        let body = json!({
+            "model": "deepseek-v4-flash",
+            "max_tokens": 64,
+            "messages": [{
+                "role": "assistant",
+                "content": [
+                    {"type": "thinking", "thinking": "I should call the tool."},
+                    {"type": "tool_use", "id": "call_123", "name": "get_weather", "input": {"location": "Tokyo"}}
+                ]
+            }]
+        });
+
+        let transformed =
+            transform_claude_request_for_api_format(body, &provider, "openai_chat", None, None)
+                .unwrap();
+
+        let msg = &transformed["messages"][0];
+        assert_eq!(msg["reasoning_content"], "I should call the tool.");
+        assert!(msg.get("tool_calls").is_some());
+    }
 }