New runtime slice #

Read ../docs/runtime-v2/STATUS.md and ../docs/runtime-v2/HANDOFF.md first. This crate is an additive replacement boundary, not yet the live daemon.

The producer had no Rust toolchain. Compile, format and run the real Rust tests before expanding the design; do not cite the Python peer tests as Rust integration coverage. Keep core invariants in Rust and ordinary policies in editable Python. No SQL transaction or domain mutation lock across a hook. No automatic replay of arbitrary cells. Preserve scratchpad/workbench-output versus explicit speech. A missing required guard holds its effect. Hook-only replacement pins in-flight cells and must not wipe a compatible workbench namespace.

Add hooks only with their real domain, typed input/result and failure contract. Do not add an empty facade for every future slot. The Python test peer is not production orchestration. Do not migrate or replace the old memory DB until a deterministic importer/cutover is tested.