CUBELinux-2
308e20852c
feat(cubesys): Task 5 transactions (BEGIN/COMMIT/ROLLBACK) + HELLO identity wiring
- Session gains txn: Option<Txn> (BEGIN snapshot + buffered ops) and
identity: Option<TenantIdentity> (owner enforcement hook for Tasks 6+).
- prog/write/del buffer into the open txn; commit_txn applies the whole
batch under one write lock + a SINGLE WalOp::Txn entry (atomic + durable
replay). ROLLBACK discards. Reads consult the BEGIN snapshot (isolation).
- cube-server: HELLO-resolved tenant yields Some(ts); default-tenant path
consistent; Session built once per connection so txns span frames.
- WalEntry gains batch field; decode_wal + encode_wal handle Txn replay.
- 4 new T5 tests: buffer/commit, rollback, snapshot isolation, durable
reopen via WAL replay. ./check quick green.