Fallback PMA URL host to reachable 8443 domain

scripts/pma-gateway/create_pma_gateway.sh

@@ -556,6 +556,46 @@ if [[ "$URL_HOST" =~ ^(.+):[0-9]+$ ]]; then
     URL_HOST="${BASH_REMATCH[1]}"
 fi
 
+# Best-effort fallback: if preferred host is not reachable on 8443,
+# try other known domain candidates before printing final gateway URL.
+if command -v timeout >/dev/null 2>&1; then
+    URL_HOST_CANDIDATES=()
+    URL_HOST_SEEN="|"
+    for candidate in "$URL_HOST" "$ENV_HOST" "${DOMAIN_CANDIDATES[@]}"; do
+        candidate="${candidate#https://}"
+        candidate="${candidate#http://}"
+        candidate="${candidate%%/*}"
+        if [[ "$candidate" =~ ^(.+):[0-9]+$ ]]; then
+            candidate="${BASH_REMATCH[1]}"
+        fi
+
+        if [[ -z "$candidate" ]] || [[ "$URL_HOST_SEEN" == *"|$candidate|"* ]]; then
+            continue
+        fi
+
+        # Restrict to simple host/domain tokens for safe /dev/tcp probing.
+        if [[ ! "$candidate" =~ ^[A-Za-z0-9._-]+$ ]]; then
+            continue
+        fi
+
+        URL_HOST_CANDIDATES+=("$candidate")
+        URL_HOST_SEEN="${URL_HOST_SEEN}${candidate}|"
+    done
+
+    SELECTED_URL_HOST=""
+    for candidate in "${URL_HOST_CANDIDATES[@]}"; do
+        if timeout 4 bash -c "exec 3<>/dev/tcp/$candidate/8443" >/dev/null 2>&1; then
+            SELECTED_URL_HOST="$candidate"
+            break
+        fi
+    done
+
+    if [[ -n "$SELECTED_URL_HOST" ]] && [[ "$SELECTED_URL_HOST" != "$URL_HOST" ]]; then
+        echo "WARNING: Preferred URL host '$URL_HOST' is not reachable on 8443. Using '$SELECTED_URL_HOST' instead." >&2
+        URL_HOST="$SELECTED_URL_HOST"
+    fi
+fi
+
 echo "INFO: Gateway URL host selected: $URL_HOST" >&2
 URL="https://$URL_HOST:8443/access-db-$SLUG.php?token=$token"
 echo "$URL"