fix(platform): sanitize Spring mail test failures

src/main/java/com/lab/labtimesheet/feature/integration/controller/SmtpController.java

@@ -9,6 +9,7 @@ import com.lab.labtimesheet.feature.integration.model.dto.SmtpForm;
 import com.lab.labtimesheet.feature.integration.service.SmtpConfigurationService;
 import jakarta.servlet.http.HttpSession;
 import jakarta.validation.Valid;
+import org.springframework.mail.MailException;
 import org.springframework.stereotype.Controller;
 import org.springframework.ui.Model;
 import org.springframework.validation.BindingResult;
@@ -76,7 +77,7 @@ class SmtpController {
         try {
             smtp.testDraft(action.getDraftId(), adminId(principal), principal.getName());
             return "redirect:/admin/smtp?tested";
-        } catch (IllegalArgumentException | IllegalStateException failure) {
+        } catch (IllegalArgumentException | IllegalStateException | MailException failure) {
             bindingResult.reject("smtp.test.failed", TEST_FAILURE_MESSAGE);
             return renderActionError(model, bindingResult);
         }

src/test/java/com/lab/labtimesheet/feature/integration/controller/SmtpOnboardingWebIntegrationTest.java

@@ -26,6 +26,7 @@ import org.springframework.boot.webmvc.test.autoconfigure.AutoConfigureMockMvc;
 import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Import;
 import org.springframework.context.annotation.Primary;
+import org.springframework.mail.MailSendException;
 import org.springframework.test.annotation.DirtiesContext;
 import org.springframework.test.context.ActiveProfiles;
 import org.springframework.test.web.servlet.MockMvc;
@@ -158,7 +159,7 @@ class SmtpOnboardingWebIntegrationTest {
                 .andReturn().getResponse().getContentAsString();
         String draftId = html.replaceAll("(?s).*name=\"draftId\" value=\"([0-9]+)\".*", "$1");
         String rawDiagnostic = "AUTH rejected for smtp-secret-raw-diagnostic";
-        probe.failureMessage = rawDiagnostic;
+        probe.failure = new MailSendException(rawDiagnostic);
 
         mockMvc.perform(post("/admin/smtp/test")
                         .with(user("admin@example.com").roles("ADMIN"))
@@ -185,12 +186,12 @@ class SmtpOnboardingWebIntegrationTest {
 
     static final class RecordingProbe implements SmtpProbe {
         private final List<String> recipients = new ArrayList<>();
-        private String failureMessage;
+        private MailSendException failure;
 
         @Override
         public void send(SmtpConnection connection, String recipient, String subject, String body) {
-            if (failureMessage != null) {
-                throw new IllegalStateException(failureMessage);
+            if (failure != null) {
+                throw failure;
             }
             recipients.add(recipient);
         }