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systemic-game-design-course/course/08-push-chains/reference/ts/README.md
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Lucas WintherandClaude Fable 5.2 8467c7929e fix(puzzle): an object steps once per movement phase; negated conversion is settled per object
Bug 1 (modules 08-10): a YOU object pulled by an earlier mover took a second step of its own. Level movement now keeps the ids that stepped in a committed plan this phase; such a YOU object starts no move, and Planner try_move answers no for it. Regression: test_08x_pulled_you_moves_once (Module 8 Expansion Drop).

Bug 2 (modules 09-10): convert honoured negation only per rule, so ALL IS ROCK beat BABA IS NOT ROCK. A target Y is now skipped for an object if any active negated rule IS NOT Y names it. Module 9 and 10 references (and their drop solutions) now carry ALL, the Module 7 Expansion Drop. Regression: test_09_negated_conversion_beats_group.

Co-Authored-By: Claude Fable 5.2 <noreply@anthropic.com>
2026-11-11 09:18:00 +01:00

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# Module 8 reference engine (TypeScript)
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 package 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.ts`: the level format, object kinds and the board. Module 8 adds `Board.find`, `Board.remove`, `Board.shift`, `Board.at` and `Kind.format` (the kind as placed, for `kindsAt`).
- `movement.ts` (new): validate, then commit. `Planner` (`tryMove`, `stayingAt`, `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, and an object that has already stepped in the same move can't step again.
- `level.ts`: a level in play. Module 8 adds `Level.moveYou`: the `YOU` objects move one at a time, furthest ahead first, each planned and then committed, and an object steps at most once per move (a `YOU` object that an earlier move carried along doesn't start its own); the rules are reparsed once at the end. `hasProperty` is `false` for a destroyed object.
- `word.ts`, `parse.ts`, `resolve.ts`: unchanged.
- `index.ts`: the module's exports.
- The rest of `src/engine/`: Part I, unchanged.
- `src/content/movement.ts` (new) and `src/content/index.ts`: 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.ts`: the adapter the course tests call. Module 8 adds `move`, `posOf` and `kindsAt` on `Baba`.
Run it with the module's tests: `node tools/verify-references.mjs 08` from the course repository.