Request-level analog of SQLite's deferred transactions that Margheim invented for isolated reader/writer connection pools. Every incoming web request starts wrapped in a `connected_to(role: :reading)` block using the reader connection pool; only when a write operation occurs (via the patched `transaction` method) does it briefly switch to the writer pool, then fall back. Implemented via Rails' automatic multi-database switching initializer with a custom resolver that marks every request as a reading request.