Record stream for a dbrp that doesn't exist hangs indefinitely

Probably just need to add some sort of read timeout so that when no data arrives we error out.

Start by locating the Go code that handles record streams for a nonexistent dbrp and review how reads currently wait for data. Check existing timeout and error-handling tests, if present. Done means a missing dbrp returns an error instead of hanging indefinitely, with regression coverage for that case.

Written by the indexing model from the issue text.