Move to snapshot only

Author: nik9000

x-pack/plugin/esql/src/main/java/org/elasticsearch/xpack/esql/action/EsqlCapabilities.java

@@ -1340,7 +1340,7 @@ public enum Cap {
         /**
          * FIRST and LAST aggregate functions.
          */
-        AGG_FIRST_LAST,
+        AGG_FIRST_LAST(Build.current().isSnapshot()),
 
         /**
          * Support correct counting of skipped shards.

x-pack/plugin/esql/src/main/java/org/elasticsearch/xpack/esql/expression/function/EsqlFunctionRegistry.java

@@ -318,8 +318,6 @@ private static FunctionDefinition[][] functions() {
                 def(Avg.class, uni(Avg::new), "avg"),
                 def(Count.class, uni(Count::new), "count"),
                 def(CountDistinct.class, bi(CountDistinct::new), "count_distinct"),
-                def(First.class, bi(First::new), "first"),
-                def(Last.class, bi(Last::new), "last"),
                 def(Max.class, uni(Max::new), "max"),
                 def(Median.class, uni(Median::new), "median"),
                 def(MedianAbsoluteDeviation.class, uni(MedianAbsoluteDeviation::new), "median_absolute_deviation"),
@@ -479,6 +477,8 @@ private static FunctionDefinition[][] snapshotFunctions() {
                 // The delay() function is for debug/snapshot environments only and should never be enabled in a non-snapshot build.
                 // This is an experimental function and can be removed without notice.
                 def(Delay.class, Delay::new, "delay"),
+                def(First.class, bi(First::new), "first"),
+                def(Last.class, bi(Last::new), "last"),
                 def(Rate.class, uni(Rate::new), "rate"),
                 def(MaxOverTime.class, uni(MaxOverTime::new), "max_over_time"),
                 def(MinOverTime.class, uni(MinOverTime::new), "min_over_time"),