ESQL: unexpected Unknown column [@timestamp] when using the metrics-only rate aggregation function

[astefan]

Description

from employees | sort rate(languages)

results in

                "reason": "Found 1 problem\nline 1:23: Unknown column [@timestamp]",
                "stack_trace": "org.elasticsearch.xpack.esql.VerificationException: Found 1 problem
line 1:23: Unknown column [@timestamp]
at org.elasticsearch.xpack.esql.analysis.Analyzer.verify(Analyzer.java:203)
at org.elasticsearch.xpack.esql.analysis.Analyzer.analyze(Analyzer.java:197)

Same goes for from employees | stats rate(languages). All these errors shouldn't have happened, instead an error like "the rate aggregate[rate(languages)] can only be used within the metrics command" should have been thrown.

[elasticsearchmachine]

Pinging @elastic/es-analytical-engine (Team:Analytics)

[wchaparro]

@martijnvg ping on this one with rate

[martijnvg]

@dnhatn I think is caused by the recent changes to TS source command?