Hello.

The documentation says:

The Describe message (statement variant) specifies the name of an existing prepared statement (or an empty string for the unnamed prepared statement). The response is a ParameterDescription message describing the parameters needed by the statement
https://www.postgresql.org/docs/13/protocol-flow.html

This means that you will get a list of the types of all input parameters.
Then you just need to encode all the input parameters in accordance with the types that you received from this response.

Then this query will work correctly:

sql`SELECT ${[1, 2, 3]}::int[]`