CauslEngine: "rust-wasm" | "typescript"

Which engine's code is canonical for a graph's commits and reads (#295).

There are exactly two executors in this package, and this is the field that distinguishes them:

  • 'rust-wasm' — the Rust→WASM core (causl-core-rs, vendored as the wasm-pkg/<bridge>-bundler artefact) is canonical. Commits are applied by commit_batch inside the module and the post-state it publishes is what read returns.
  • 'typescript', an in-process TypeScript engine, is canonical. No graph this package builds answers this since causl/causl-wasm-ts#279 slice S12 deleted that engine; the value is retained because an adopter's exhaustive switch over the union keeps compiling, and because causlEngineOf still reports it for any Graph this subpath did not build.

This is the field that survives the #280 TS-free cut unchanged. #280 removed the engine option and made createCausl() fail loud, so 'typescript' is now reachable only for a foreign Graph handed to causlEngineOf — but the field, its name and its meaning are untouched, and code written against it keeps compiling and keeps being correct. Prefer branching on this rather than on the finer mode.