[killertux]

Summary

• Driver trait refactor. The DriverKind enum is gone. Each database now implements a Driver trait in its own module: URL schemes, sqlparser dialect, identifier quoting, autocomplete functions, :export sql literal rendering, and connect() → Datasource. Drivers are registered in DRIVERS. Adding a database no longer requires changes outside src/datasource/. The connection-form hint is generated from the registry, so it now also lists the postgresql: alias.
• Stoolap driver (stoolap:./data/mydb, stoolap::memory:). Stoolap is embedded and in-process, and is called through its synchronous API on the blocking pool.
  • Transactions: user statements run on a dedicated session executor that keeps BEGIN … COMMIT across execute() calls.
  • Introspection: runs SHOW TABLES / SHOW VIEWS / DESCRIBE / SHOW INDEXES on a separate auto-commit handle. Views fall back to SELECT * … LIMIT 0 for column names.
  • Results: the engine's column list decides rows vs. affected count, so INSERT … RETURNING rows are shown.
  • Cancel: fires stoolap's cancellation flag and also moves the session to a fresh executor. The engine doesn't check the flag inside joins, so without the swap the next statement would queue behind a runaway query. Any open transaction is rolled back, same as a Postgres cancel.
  • Dependency: stoolap is pinned to =0.4.2 (pre-1.0, breaking minor releases) with default features off. The defaults install a jemalloc #[global_allocator] and the stoolap CLI. It adds 26 crates and changes no existing versions.
• Bump to 0.19.0 (minor: new database support).

Known limitations (documented in README)

• Cancel can't stop a statement stoolap doesn't check (e.g. joins). The statement keeps running on its abandoned executor until it finishes.
• Stoolap locks the database directory, so rowdy and another process can't open the same database at once.
• There are no catalogs or schemas: tables show under a single main. Views report no column types, and primary keys aren't listed as indices.

Test plan

• cargo fmt && cargo clippy --all-targets -- -D warnings && cargo test: 674 tests pass locally, including 8 new stoolap tests (introspection, cell decoding, transactions across calls, reset rollback, file persistence + lock release, URL parsing) and 3 new driver-registry tests
• Manual (tmux, throwaway HOME): created a stoolap: connection, Ctrl+T test showed ✓ Connected, ran CREATE/INSERT/SELECT (int/text/JSON/timestamp/NULL render), and expanded the schema tree down to columns with types
• Manual: :export sql on a stoolap result, then re-import it into a fresh stoolap::memory:
• Manual: :cancel on a long stoolap join, then confirm the next statement runs immediately