- verify-references --expansion overlays expansion/solution on each reference and runs the
  cumulative tests plus the drop test; refuses a solution that touches src/engine/
- CI job verify-expansions
- README: workspace-template + git init step, tool list, repo disclaimer link
- Cargo.lock for every Rust reference (staged with the reference, pins serde for rustc 1.85.1)

Co-Authored-By: Claude Opus 5.5 <[email protected]>

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src

feat: module 08 push chains

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.course.json

feat: module 08 push chains

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.gitignore

feat: module 08 push chains

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Cargo.lock

feat(ci): verify Expansion Drop solutions; README quick start, disclaimer link; Rust reference lockfiles

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Cargo.toml

feat: module 08 push chains

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README.md

feat: module 08 push chains

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README.md

Module 8 reference engine (Rust)

The course's own engine as of the end of Module 8. Part I's card engine is unchanged, and all of its tests still pass. The Part II engine in src/engine/puzzle/ now moves objects: each YOU object's move is planned in full, push chain and all, and only then committed. Module 7's reference was the starting point, so a diff between the two shows what this module adds.

cards/ (at the crate root; not in this directory): Part I's card data, a copy of course/cards/ staged by tools/verify-references.mjs. Part II doesn't read it.
src/engine/puzzle/: the Part II engine. It names no noun: the engine's own words are the operators IS, AND, NOT, the meta-noun TEXT, the property PUSH of the base rule TEXT IS PUSH, and from Module 8 the property YOU, which picks the objects that move.
- grid.rs: the level format, object kinds and the board. Module 8 adds Board::find, Board::remove, Board::shift, Board::at and Display for Kind (the kind as placed, for kinds_at).
- movement.rs (new): validate, then commit. Planner (try_move, staying_at, destroy, has), Step, Plan, Response and Dir. The planner reads the board and plans one step at a time; for each step it runs content's movement responses in order, and rolls back everything a step added if a response blocks it. The edge of the level blocks every step.
- level.rs: a level in play. Module 8 adds Level::move_you: the YOU objects move one at a time, furthest ahead first, each planned and then committed; the rules are reparsed once at the end. has_property is false for a destroyed object.
- word.rs, parse.rs, resolve.rs: unchanged.
- mod.rs: the module's exports.
The rest of src/engine/: Part I, unchanged.
src/content/movement.rs (new) and src/content/mod.rs: the movement responses, in the order the engine runs them: OPEN/SHUT, PUSH, STOP. What a property does when something moves is content, not engine.
src/content/words.json: Module 8 adds OPEN and SHUT.
src/harness.rs: the adapter the course tests call. Module 8 adds Baba::move_dir, Baba::pos_of, Baba::kinds_at, and re-exports Dir.

Run it with the module's tests: node tools/verify-references.mjs 08 from the course repository.