```
from employees | keep * | mv_expand first_name
```

throws UnresolvedException:

```
org.elasticsearch.xpack.ql.capabilities.UnresolvedException: Invalid call to attribute on an unresolved object ?*
        at org.elasticsearch.xpack.ql.expression.UnresolvedNamedExpression.toAttribute(UnresolvedNamedExpression.java:44)
        at org.elasticsearch.xpack.ql.expression.Expressions.asAttributes(Expressions.java:40)
        at org.elasticsearch.xpack.ql.plan.logical.Project.output(Project.java:62)
        at org.elasticsearch.xpack.esql.plan.logical.MvExpand.<init>(MvExpand.java:31)
        at org.elasticsearch.xpack.esql.parser.LogicalPlanBuilder.lambda$visitMvExpandCommand$3(LogicalPlanBuilder.java:154)
        at org.elasticsearch.xpack.esql.parser.LogicalPlanBuilder.visitCompositeQuery(LogicalPlanBuilder.java:89)
        at org.elasticsearch.xpack.esql.parser.LogicalPlanBuilder.visitCompositeQuery(LogicalPlanBuilder.java:66)
        at org.elasticsearch.xpack.esql.parser.EsqlBaseParser$CompositeQueryContext.accept(EsqlBaseParser.java:232)
        at org.elasticsearch.xpack.ql.parser.ParserUtils.typedParsing(ParserUtils.java:51)
        at org.elasticsearch.xpack.esql.parser.LogicalPlanBuilder.plan(LogicalPlanBuilder.java:73)
        at org.elasticsearch.xpack.esql.parser.LogicalPlanBuilder.visitSingleStatement(LogicalPlanBuilder.java:82)
        at org.elasticsearch.xpack.esql.parser.LogicalPlanBuilder.visitSingleStatement(LogicalPlanBuilder.java:66)
        at org.elasticsearch.xpack.esql.parser.EsqlBaseParser$SingleStatementContext.accept(EsqlBaseParser.java:169)
```

The problem is that MV_EXPAND tries to pre-calculate the output too early, when the resolution did not happen yet.
x-pack/plugin/esql/src/main/java/org/elasticsearch/xpack/esql/plan/logical/MvExpand.java
private final NamedExpression target;
    private final Attribute expanded;
    private final List<Attribute> output;
    public MvExpand(Source source, LogicalPlan child, NamedExpression target, Attribute expanded) {
        super(source, child);
        this.target = target;
        this.expanded = expanded;
        this.output = calculateOutput(child.output(), target, expanded);
    }
    public static List<Attribute> calculateOutput(List<Attribute> input, NamedExpression target, Attribute expanded) {
        List<Attribute> result = new ArrayList<>();
        for (Attribute attribute : input) {
            if (attribute.name().equals(target.name())) {
                result.add(expanded);
            } else {
                result.add(attribute);
            }
        }
        return result;
    }
    public NamedExpression target() {
        return target;
    }
    public Attribute expanded() {
        return expanded;