fix(opensearch): readable advice when both engines are unreachable (#37636)

The both-down message read "Neither Elasticsearch nor OpenSearch could not be
reached", a double negative that states the opposite. It now says both could
not be reached and gives each engine's reason.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

Author: fabrizzio-dotCMS

dotCMS/src/main/java/com/dotcms/content/index/migration/MirrorStatus.java

@@ -263,10 +263,19 @@ public static Verdict verdictFor(final EngineCopy es, final EngineCopy os) {
      */
     public static String unmeasuredAdvice(final String what, final String name, final EngineCopy es,
             final EngineCopy os) {
-        final String engines = !es.wasRead() && !os.wasRead()
-                ? "Neither Elasticsearch nor OpenSearch"
-                : (!es.wasRead() ? ELASTICSEARCH : OPENSEARCH);
-        final String reason = !es.wasRead() ? es.unavailableReason() : os.unavailableReason();
+        final String engines;
+        final String reason;
+        if (!es.wasRead() && !os.wasRead()) {
+            engines = "Both Elasticsearch and OpenSearch";
+            reason = ELASTICSEARCH + ": " + es.unavailableReason() + "; " + OPENSEARCH + ": "
+                    + os.unavailableReason();
+        } else if (!es.wasRead()) {
+            engines = ELASTICSEARCH;
+            reason = es.unavailableReason();
+        } else {
+            engines = OPENSEARCH;
+            reason = os.unavailableReason();
+        }
         return String.format("%s could not be reached (%s), so the two copies of %s '%s' could not "
                 + "be compared. Restore access and re-run this check; do not rebuild the index on the "
                 + "strength of this reading.", engines, reason, what, name);

dotCMS/src/test/java/com/dotcms/content/index/migration/ContentIndexMirrorReconcilerTest.java

@@ -583,5 +583,9 @@ public void bothEnginesUnreachable_rowsStillReported() {
         assertEquals(Verdict.UNMEASURED, mirrors.statuses().get(0).verdict());
         assertFalse(mirrors.statuses().get(0).es().wasRead());
         assertFalse(mirrors.statuses().get(0).os().wasRead());
+        final String advice = mirrors.statuses().get(0).recommendation();
+        assertTrue(advice, advice.startsWith("Both Elasticsearch and OpenSearch could not be reached"));
+        assertTrue(advice, advice.contains("Elasticsearch: es down"));
+        assertTrue(advice, advice.contains("OpenSearch: os down"));
     }
 }