fix: defer response body closure only when necessary to prevent premature stream termination

handlers/anthropic.go

@@ -290,9 +290,9 @@ func handleStreaming(
 		logger.Warn("[ANTHROPIC] Stream error [IP: %s]: %v", c.IP(), err)
 		return c.Status(fiber.StatusBadGateway).SendString("upstream error")
 	}
-	defer resp.Body.Close()
 
 	if resp.StatusCode != 200 {
+		defer resp.Body.Close()
 		body, _ := io.ReadAll(resp.Body)
 		logger.Warn("[ANTHROPIC] Stream upstream %d [IP: %s]: %s", resp.StatusCode, c.IP(), string(body))
 		return c.Status(resp.StatusCode).Send(body)
@@ -308,6 +308,8 @@ func handleStreaming(
 	c.Set("Connection", "keep-alive")
 
 	c.Response().SetBodyStreamWriter(func(w *bufio.Writer) {
+		defer resp.Body.Close()
+
 		scanner := bufio.NewScanner(resp.Body)
 
 		const maxScanTokenSize = 4 * 1024 * 1024 // 4 MB — Claude Code tool calls produce large chunks