Very cool. One question that comes up for me is whether pg_lake expects to control the Iceberg metadata, or whether it can be used purely as a read layer. If I make schema updates and partition changes to iceberg directly, without going through pg_lake, will pg_lake's catalog correctly reflect things right away?

We have some level of external iceberg table read-only support, but it is limited at the moment. See this example/caveat: https://github.com/Snowflake-Labs/pg_lake/blob/main/docs/fil...

You can use it as a read layer for for specific metadata JSON URL or a table in a REST catalog. The latter got merged quite recently, not yet in docs.