fn ensure_table_definition_writable(schema: &str, table: &str) -> Result<()>Expand description
ensure_table_writable plus the definition guard for system-defined
tables: user CREATE, ALTER and RENAME-into are rejected so the canonical
schema cannot be squatted or mutated. DROP and TRUNCATE stay allowed — the
next INSERT recreates the table canonically, which is also the recovery
path if the canonical definition changes across an upgrade.