fix: 외부 수집 요청 헤더 중복 제거

src/main/java/com/hlab/yanalyst/global/config/RestTemplateConfig.java

@@ -4,6 +4,7 @@ import org.springframework.boot.web.client.RestTemplateBuilder;
 import org.springframework.beans.factory.annotation.Value;
 import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Configuration;
+import org.springframework.http.HttpHeaders;
 import org.springframework.web.client.RestTemplate;
 
 import java.time.Duration;
@@ -17,7 +18,11 @@ public class RestTemplateConfig {
                 .connectTimeout(Duration.ofSeconds(20))
                 .readTimeout(Duration.ofSeconds(120))
                 .additionalInterceptors((request, body, execution) -> {
-                    request.getHeaders().add("User-Agent", "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/120.0.0.0 Safari/537.36");
+                    if (!request.getHeaders().containsKey(HttpHeaders.USER_AGENT)) {
+                        request.getHeaders().set(HttpHeaders.USER_AGENT,
+                                "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 "
+                                        + "(KHTML, like Gecko) Chrome/120.0.0.0 Safari/537.36");
+                    }
                     return execution.execute(request, body);
                 })
                 .build();

src/test/java/com/hlab/yanalyst/global/config/RestTemplateConfigTest.java

@@ -0,0 +1,38 @@
+package com.hlab.yanalyst.global.config;
+
+import org.junit.jupiter.api.Test;
+import org.springframework.boot.web.client.RestTemplateBuilder;
+import org.springframework.http.HttpEntity;
+import org.springframework.http.HttpHeaders;
+import org.springframework.http.HttpMethod;
+import org.springframework.http.HttpStatus;
+import org.springframework.http.MediaType;
+import org.springframework.test.web.client.MockRestServiceServer;
+import org.springframework.web.client.RestTemplate;
+
+import java.util.List;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.springframework.test.web.client.match.MockRestRequestMatchers.requestTo;
+import static org.springframework.test.web.client.response.MockRestResponseCreators.withSuccess;
+
+class RestTemplateConfigTest {
+
+    @Test
+    void preservesCallerUserAgentWithoutAddingDuplicateHeader() {
+        RestTemplate restTemplate = new RestTemplateConfig().restTemplate(new RestTemplateBuilder());
+        MockRestServiceServer server = MockRestServiceServer.bindTo(restTemplate).build();
+        server.expect(requestTo("https://example.com/feed"))
+                .andExpect(request -> assertThat(request.getHeaders().get(HttpHeaders.USER_AGENT))
+                        .isEqualTo(List.of("social-feed-agent")))
+                .andRespond(withSuccess("ok", MediaType.TEXT_PLAIN));
+
+        HttpHeaders headers = new HttpHeaders();
+        headers.set(HttpHeaders.USER_AGENT, "social-feed-agent");
+        var response = restTemplate.exchange("https://example.com/feed", HttpMethod.GET,
+                new HttpEntity<>(headers), String.class);
+
+        assertThat(response.getStatusCode()).isEqualTo(HttpStatus.OK);
+        server.verify();
+    }
+}