lattice AGENTS.md

Lattice — how to work in this repo

Lattice is a kit for building isometric, deterministic, zero-asset games in TypeScript. Nine small libraries that compose, and a real game built from nothing but them.

This file is the constitution. It is written for agents first and humans second, because agents outnumber humans here. Read it before you touch anything. It is short on purpose.

• What each package is → .lattice/kit.json (machine-readable), README.md § The nine packages, and each package's own README.md. The cross-package contracts are in docs/SEAMS.md
• What to work on next → .lattice/tasks.json
• Where the build is → .lattice/state.json
• How one work cycle runs → docs/LOOP.md

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The eleven non-negotiables

These are not preferences. A change that breaks one of these is reverted, not debated.

1. Determinism is a feature, not an accident. Math.random(), Date.now(), and performance.now() are banned inside every package's src/. Randomness comes from a seeded Rng passed in by the caller; time arrives as a parameter. This is enforced by npm run lint. A game built on Lattice must be able to replay a session from a seed and an input log and land on the same pixel.

   And it has two tiers, because the language only promises so much. ECMA-262 specifies + - * /, Math.sqrt, Math.imul and the bitwise operators exactly. It explicitly does not require sin, cos, pow, exp or log to be correctly rounded, so two conforming engines may disagree in the last bit.

   	arithmetic	promise	may reach
   Tier A	+ - * /, sqrt, imul, bitwise	bit-identical on every engine	hashes, save files, replays, anything
   Tier B	sin, cos, pow, exp, log, …	correct to within an ulp or so	pixels only — never hashed, never persisted

   Tier B is not banned; a cost curve is b · r^k and there is no honest way around that. It is required to declare itself: mark the site @tier-b and the linter is satisfied. That makes every one of them greppable, so an auditor can ask of each in turn whether it ever reaches a save file.