createSavepoint method
Creates a savepoint named name inside this transaction.
Returns false immediately if the transaction is no longer active
(committed, rolled back, or in a failed state).
The savepoint name MUST match the identifier grammar enforced by the
engine (ASCII letter or _, then letters/digits/_, ≤128 chars).
Names containing semicolons, quotes or whitespace are rejected at the
FFI boundary (B1 fix in v3.1).
Implementation
bool createSavepoint(String name) {
if (_state != _State.active) return false;
return _backend.createSavepoint(_txnId, name);
}