Block readiness on bad initial file settings (#107775)

If file settings have an update that fails, existing applied file
settings continue to work. But if the initial file settings fail to
process, readiness should be blocked. This commit adjusts readiness to
look for this special initialization case.

relates #107738

Author: rjernst

server/src/internalClusterTest/java/org/elasticsearch/readiness/ReadinessClusterIT.java

@@ -251,7 +251,6 @@ private void writeFileSettings(String json) throws Exception {
         logger.info("--> New file settings: [{}]", Strings.format(json, version));
     }
 
-    @AwaitsFix(bugUrl = "https://github.com/elastic/elasticsearch/issues/107744")
     public void testNotReadyOnBadFileSettings() throws Exception {
         internalCluster().setBootstrapMasterNodeIndex(0);
         logger.info("--> start data node / non master node");

server/src/main/java/org/elasticsearch/cluster/metadata/ReservedStateMetadata.java

@@ -46,6 +46,8 @@ public record ReservedStateMetadata(
     ReservedStateErrorMetadata errorMetadata
 ) implements SimpleDiffable<ReservedStateMetadata>, ToXContentFragment {
 
+    public static final Long NO_VERSION = Long.MIN_VALUE; // use min long as sentinel for uninitialized version
+
     private static final ParseField VERSION = new ParseField("version");
     private static final ParseField HANDLERS = new ParseField("handlers");
     private static final ParseField ERRORS_METADATA = new ParseField("errors");
@@ -209,7 +211,7 @@ public static class Builder {
          */
         public Builder(String namespace) {
             this.namespace = namespace;
-            this.version = -1L;
+            this.version = NO_VERSION;
             this.handlers = new HashMap<>();
             this.errorMetadata = null;
         }

server/src/main/java/org/elasticsearch/readiness/ReadinessService.java

@@ -254,7 +254,7 @@ public void clusterChanged(ClusterChangedEvent event) {
     // protected to allow mock service to override
     protected boolean areFileSettingsApplied(ClusterState clusterState) {
         ReservedStateMetadata fileSettingsMetadata = clusterState.metadata().reservedStateMetadata().get(FileSettingsService.NAMESPACE);
-        return fileSettingsMetadata != null;
+        return fileSettingsMetadata != null && fileSettingsMetadata.version().equals(ReservedStateMetadata.NO_VERSION) == false;
     }
 
     private void setReady(boolean ready) {

server/src/test/java/org/elasticsearch/cluster/metadata/ReservedStateMetadataTests.java

@@ -20,6 +20,7 @@
 import java.util.Collections;
 import java.util.List;
 
+import static org.elasticsearch.cluster.metadata.ReservedStateMetadata.NO_VERSION;
 import static org.hamcrest.Matchers.equalTo;
 import static org.hamcrest.Matchers.not;
 
@@ -78,7 +79,7 @@ public void testXContent() throws IOException {
 
     public void testReservedStateVersionWithError() {
         final ReservedStateMetadata meta = createRandom(false, true);
-        assertEquals(-1L, meta.version().longValue());
+        assertEquals(NO_VERSION.longValue(), meta.version().longValue());
     }
 
     private static ReservedStateMetadata createRandom(boolean addHandlers, boolean addErrors) {

server/src/test/java/org/elasticsearch/cluster/metadata/ToAndFromJsonMetadataTests.java

@@ -776,7 +776,7 @@ public void testToXContentAPIReservedMetadata() throws IOException {
                 },
                 "reserved_state" : {
                   "namespace_one" : {
-                    "version" : -1,
+                    "version" : -9223372036854775808,
                     "handlers" : {
                       "one" : {
                         "keys" : [
@@ -801,7 +801,7 @@ public void testToXContentAPIReservedMetadata() throws IOException {
                     }
                   },
                   "namespace_two" : {
-                    "version" : -1,
+                    "version" : -9223372036854775808,
                     "handlers" : {
                       "three" : {
                         "keys" : [