fix(etl): enforce accepted status URL invariant

etl-service/src/main/java/com/xtrmetl/etl/job/EtlJobAcceptedResponse.java

@@ -8,7 +8,7 @@
  *
  * @param jobRecordId opaque durable job identifier
  * @param jobStatus current stable job status
- * @param statusUrl relative status-monitor resource URL
+ * @param statusUrl origin-relative status-monitor resource URL beginning with exactly one slash
  */
 public record EtlJobAcceptedResponse(
         UUID jobRecordId,
@@ -21,11 +21,18 @@ public record EtlJobAcceptedResponse(
      *
      * @param jobRecordId opaque durable job identifier
      * @param jobStatus current stable job status
-     * @param statusUrl relative status-monitor resource URL
+     * @param statusUrl origin-relative status-monitor resource URL beginning with exactly one slash
+     * @throws IllegalArgumentException when {@code statusUrl} is blank or is not origin-relative
      */
     public EtlJobAcceptedResponse {
         Objects.requireNonNull(jobRecordId, "jobRecordId must not be null");
         Objects.requireNonNull(jobStatus, "jobStatus must not be null");
         Objects.requireNonNull(statusUrl, "statusUrl must not be null");
+        if (statusUrl.isBlank()) {
+            throw new IllegalArgumentException("statusUrl must not be blank");
+        }
+        if (!statusUrl.startsWith("/") || statusUrl.startsWith("//")) {
+            throw new IllegalArgumentException("statusUrl must be origin-relative");
+        }
     }
 }

etl-service/src/test/java/com/xtrmetl/etl/job/EtlJobAcceptedResponseStatusUrlTest.java

@@ -0,0 +1,64 @@
+package com.xtrmetl.etl.job;
+
+import org.junit.jupiter.api.Test;
+
+import java.util.List;
+import java.util.UUID;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+
+/**
+ * Verifies that accepted durable-job representations expose only valid origin-relative status URLs.
+ */
+class EtlJobAcceptedResponseStatusUrlTest {
+
+    private static final UUID JOB_RECORD_ID = UUID.fromString(
+            "cf4f083f-8c90-4f34-a8b6-b53761de44ef"
+    );
+
+    @Test
+    void retainsValidOriginRelativeStatusUrl() {
+        String statusUrl = "/api/etl/jobs/" + JOB_RECORD_ID;
+
+        EtlJobAcceptedResponse response = new EtlJobAcceptedResponse(
+                JOB_RECORD_ID,
+                EtlJobStatus.PENDING,
+                statusUrl
+        );
+
+        assertEquals(statusUrl, response.statusUrl());
+    }
+
+    @Test
+    void rejectsBlankStatusUrls() {
+        for (String invalidStatusUrl : List.of("", " ", "\t\n")) {
+            assertThrows(
+                    IllegalArgumentException.class,
+                    () -> new EtlJobAcceptedResponse(
+                            JOB_RECORD_ID,
+                            EtlJobStatus.PENDING,
+                            invalidStatusUrl
+                    )
+            );
+        }
+    }
+
+    @Test
+    void rejectsNonOriginRelativeStatusUrls() {
+        for (String invalidStatusUrl : List.of(
+                "https://example.test/api/etl/jobs/" + JOB_RECORD_ID,
+                "//example.test/api/etl/jobs/" + JOB_RECORD_ID,
+                "api/etl/jobs/" + JOB_RECORD_ID
+        )) {
+            assertThrows(
+                    IllegalArgumentException.class,
+                    () -> new EtlJobAcceptedResponse(
+                            JOB_RECORD_ID,
+                            EtlJobStatus.PENDING,
+                            invalidStatusUrl
+                    )
+            );
+        }
+    }
+}