Fix cleanup frequency validation to match UI bounds

plugin/src/main/java/jenkins/plugins/openstack/compute/JCloudsCloud.java

@@ -635,13 +635,14 @@ public FormValidation doCheckCleanfreq(@QueryParameter String value) {
 
             try {
                 long parsedCleanFreq = Long.parseLong(value);
-                if (parsedCleanFreq == 0) {
-                    NumberFormatException nfe =
-                            new NumberFormatException("cleanfreq should be strictly greater than 0");
+                // Keep server-side validation consistent with the bounds in config.jelly.
+                if (parsedCleanFreq < 10 || parsedCleanFreq > 1200) {
+                    NumberFormatException nfe = new NumberFormatException("cleanfreq must be between 10 and 1200");
                     throw nfe;
                 }
             } catch (NumberFormatException ex) {
-                return FormValidation.error(ex, "Clean frequency must be an integer strictly greater than 0 (>=1)");
+                return FormValidation.error(
+                        ex, "Cleanup frequency must be a whole number between 10 and 1200 seconds.");
             }
             return FormValidation.ok();
         }

plugin/src/main/resources/jenkins/plugins/openstack/compute/JCloudsCloud/help-cleanfreq.html

@@ -1,3 +1,4 @@
 <div>
-  Clean frequency of pending VM (seconds)
+  <p>Interval in seconds between background cleanup checks for this cloud, including instances awaiting deletion and leftover floating IPs. For example, 60 schedules checks roughly once a minute. This setting does not control the agent idle timeout.</p>
+  <p><strong>Minimum:</strong> 10 seconds &middot; <strong>Maximum:</strong> 1200 seconds &middot; <strong>Default:</strong> 10 seconds</p>
 </div>

plugin/src/test/java/jenkins/plugins/openstack/compute/JCloudsCloudTest.java

@@ -80,6 +80,33 @@ public class JCloudsCloudTest {
     @Rule
     public PluginTestRule j = new PluginTestRule();
 
+    @Test
+    public void validateCleanupFrequency() {
+        DescriptorImpl desc = j.getCloudDescriptor();
+
+        for (String value : new String[] {
+            "-1",
+            "-10",
+            "-9223372036854775808",
+            "0",
+            "1",
+            "9",
+            "1201",
+            "3600",
+            "9223372036854775807",
+            "",
+            " ",
+            "abc",
+            "1.5",
+            "9223372036854775808"
+        }) {
+            assertEquals(value, FormValidation.Kind.ERROR, desc.doCheckCleanfreq(value).kind);
+        }
+        for (String value : new String[] {"10", "11", "60", "1199", "1200"}) {
+            assertEquals(value, FormValidation.Kind.OK, desc.doCheckCleanfreq(value).kind);
+        }
+    }
+
     @Test
     public void failToTestConnection() {
         DescriptorImpl desc = j.getCloudDescriptor();