Function require_file_initialized 

pub fn require_file_initialized<E>(
    connection: &Connection,
    busy_timeout: Duration,
    schema: SchemaVersion,
) -> Result<(), InitializationError<E>>

Require an exact schema version on a file-backed connection without initializing it.

Ready databases avoid the sidecar lock. When initialization is in flight, this waits for its persistent lease and validates the marker after the writer releases it. If no initializer owns the lease, an absent marker is reported here instead of allowing a read-only consumer to fail later on a missing application table.