Preserve reasoning_content with minimal-format diffs

pkg/providers/openai_compat/provider.go

@@ -301,6 +301,7 @@ func parseResponse(body []byte) (*LLMResponse, error) {
 type openaiMessage struct {
 	Role       string     `json:"role"`
 	Content    string     `json:"content"`
+	Reasoning  string     `json:"reasoning_content,omitempty"`
 	ToolCalls  []ToolCall `json:"tool_calls,omitempty"`
 	ToolCallID string     `json:"tool_call_id,omitempty"`
 }
@@ -314,6 +315,7 @@ func stripSystemParts(messages []Message) []openaiMessage {
 		out[i] = openaiMessage{
 			Role:       m.Role,
 			Content:    m.Content,
+			Reasoning:  m.ReasoningContent,
 			ToolCalls:  m.ToolCalls,
 			ToolCallID: m.ToolCallID,
 		}

pkg/tools/toolloop.go

@@ -106,6 +106,7 @@ func RunToolLoop(
 			Role:    "assistant",
 			Content: response.Content,
 		}
+		assistantMsg.ReasoningContent = response.ReasoningContent
 		for _, tc := range normalizedToolCalls {
 			argumentsJSON, _ := json.Marshal(tc.Arguments)
 			assistantMsg.ToolCalls = append(assistantMsg.ToolCalls, providers.ToolCall{