The internal database defaults to a temporary file that is deleted on
shutdown. Plugin writes that expect persistence currently vanish silently.
Detect such writes via an `internal_ephemeral_writes()` context manager
in `datasette.database`: Datasette wraps `_refresh_schemas` (its own
catalog/metadata writes) with the marker, and `Database.execute_write_fn`
prints a one-time stderr warning when a write hits a `is_temp_disk`
database without the marker set. The warning recommends restarting with
`--internal path/to/file.db` for persistence.
