Cheese Rolling rules: a tested `cheese-rolling/hill.js` where you chase a seeded rolling cheese down a steep hill, dodging tussocks, and catch it before the bottom, in a two-file pull with a test file that runs in under a second #359

I added cheese-rolling/hill.js and cheese-rolling/hill.test.mjs and pushed them. The nine tests pass, and bun test cheese-rolling/hill.test.mjs ran in 127–130 ms on its own. I did not run the full bun test. bun scripts/gate.ts doesn't exist in this clone, and bun x tsc --noEmit only printed its help text (there is no tsconfig), so neither check ran.

What changed

• hill.js has the same UMD shape as tide-crossing/causeway.js and exports CheeseRolling in the browser. Its only randomness is a seeded mulberry32 generator, so a seed always gives the same hill and cheese path. It exports start, step, solve, describe, ACTIONS and MAX_LEVEL.
• start(seed, level) gives a hill with at least 5 lanes and 20 rows (more at higher levels, which also add tussocks and longer trips), plus the tussocks, the runner's start, the cheese's start and its path. Tussocks never sit on the cheese path. The runner starts at row 4 and the cheese at row 0, so the cheese rolls down onto the runner and the runner has to be on its square when it arrives. A runner that just moves down alongside the cheese can never catch it, so I chose this over a runner that starts above the cheese. Say if you want a different set-up.
• Each level is generated, solved by breadth-first search, and regenerated if it can't be won. If 50 tries all fail, start falls back to a hill with no tussocks. That fallback is not proven winnable, but none of the 20 seeds tested at any level reached it.
• step(state, action) takes left, right, down or stay. It refuses with unknown-action, off-hill or game-over and returns the same state object each time.
• A tussock trips the runner for tripTicks ticks (2, rising at higher levels). During those ticks the runner stays put and the cheese keeps rolling.
• Sharing the cheese's square wins, with a line like Caught the cheese on row N at tick T. The cheese passing the bottom loses with Lost: …. State reports tick, trips and rowsLeft for the HUD.

Tests

• They cover:

- determinism, with Math.random stubbed to throw - hill shape - each refusal and its reason - the trip cost - the win line and the loss line - the HUD fields - all of seeds 1–20 at levels 0–4 winnable, by a search that only calls step

• They load no page, renderer or server.

Left out No page, catalogue entry or HUD, as the issue asks. Nothing outside cheese-rolling/ was touched.

Closes #350

I added cheese-rolling/hill.js and cheese-rolling/hill.test.mjs and pushed them. The nine tests pass, and bun test cheese-rolling/hill.test.mjs ran in 127–130 ms on its own. I did not run the full bun test. bun scripts/gate.ts doesn't exist in this clone, and bun x tsc --noEmit only printed its help text (there is no tsconfig), so neither check ran.

What changed

• hill.js has the same UMD shape as tide-crossing/causeway.js and exports CheeseRolling in the browser. Its only randomness is a seeded mulberry32 generator, so a seed always gives the same hill and cheese path. It exports start, step, solve, describe, ACTIONS and MAX_LEVEL.
• start(seed, level) gives a hill with at least 5 lanes and 20 rows (more at higher levels, which also add tussocks and longer trips), plus the tussocks, the runner's start, the cheese's start and its path. Tussocks never sit on the cheese path. The runner starts at row 4 and the cheese at row 0, so the cheese rolls down onto the runner and the runner has to be on its square when it arrives. A runner that just moves down alongside the cheese can never catch it, so I chose this over a runner that starts above the cheese. Say if you want a different set-up.
• Each level is generated, solved by breadth-first search, and regenerated if it can't be won. If 50 tries all fail, start falls back to a hill with no tussocks. That fallback is not proven winnable, but none of the 20 seeds tested at any level reached it.
• step(state, action) takes left, right, down or stay. It refuses with unknown-action, off-hill or game-over and returns the same state object each time.
• A tussock trips the runner for tripTicks ticks (2, rising at higher levels). During those ticks the runner stays put and the cheese keeps rolling.
• Sharing the cheese's square wins, with a line like Caught the cheese on row N at tick T. The cheese passing the bottom loses with Lost: …. State reports tick, trips and rowsLeft for the HUD.

Tests

• They cover:

- determinism, with Math.random stubbed to throw - hill shape - each refusal and its reason - the trip cost - the win line and the loss line - the HUD fields - all of seeds 1–20 at levels 0–4 winnable, by a search that only calls step

• They load no page, renderer or server.

Left out No page, catalogue entry or HUD, as the issue asks. Nothing outside cheese-rolling/ was touched.

Both review points are fixed on the same branch and pushed. bun test cheese-rolling/hill.test.mjs passes all 10 tests in 128 ms.

• Fallback: you were right that a bare hill with a random runner column isn't always winnable. The fallback in start() now calls a new exported bareHill(seed, level). It builds a hill with no tussocks and puts the runner on path[4], the cheese's lane at the runner's row. The runner just waits and the cheese arrives on tick 4, so the catch is guaranteed. I rewrote the comment to say so.
• Test for the fallback: a new test runs bareHill for 50 seeds at all 5 levels. It checks there are no tussocks, that solve finds a catch in 4 ticks, and that four stay steps win with the catch on row 4. The first version expected the solver's answer to be exactly four stay actions, but it found an equally short left/right route, so I assert the length instead.
• Credit: the header of hill.js now names the Cooper's Hill Cheese-Rolling tradition of Gloucestershire, next to the mulberry32 credit.