Roll-Up

Build a tiny browser game called "Roll-Up".

Game spec
---------
A katamari-style growth game in one canvas file: a glowing cyan ball steered with arrows/WASD or a touch pad (click-drag gives an impulse) rolls a 2400x2400 scrolling field of seven size-classes of objects — pebbles, coins, bottles, crates, boulders, carts and statues — drawn by a camera centred on the ball over a drifting grid and a boundary frame. Anything at most ninety percent of the ball's radius sticks on contact, adding its area (times a fatness factor) to the ball so growth is by area conservation, bumps the score by its size class, and visibly decorates the ball as a hue-fleck orbiting its surface; too-large objects are outlined red, bounce the ball back, and on hard bite half a second off the clock. Speed eases as the ball swells. A progress bar tracks the difficulty-scaled size goal (100/130/170 radius) against a 100/80/65 second timer; reaching the goal wins with a time bonus, the clock running out shows final size versus goal, and clicking rerolls a fresh scatter. Score posts to the parent on every pickup.

Hard constraints — the game will be embedded in a sandboxed iframe on a static gallery site, and a headless browser will screenshot it:

1. Output exactly ONE self-contained HTML file. All CSS and JS inline. Zero external requests: no CDNs, no external fonts, images, or sounds, no fetch/XHR/WebSocket. Any sound must be synthesized with WebAudio.
2. The iframe sandbox is "allow-scripts allow-pointer-lock" (plus an autoplay permission). So: no localStorage, cookies, or indexedDB (opaque origin — access throws); no popups, window.open, or navigation; no access to the parent page; alert()/prompt()/confirm() are silently blocked.
3. The playfield must be visible within 800 ms of load — that is when the screenshot is taken. No dead white screen. If there is a start screen, make it visually rich.
4. Controls: keyboard AND mouse must both work, plus on-screen touch buttons for phones. Call preventDefault() on game keys (arrows, space) so the page never scrolls.
5. The view is 16:9 and must scale to fill the viewport with no overflow or scrollbars.
6. Show a visible score. If the genre has a losing state, show a game-over screen with a restart (button and a key). Idle/clicker games skip game over but still need clear numeric feedback.
7. If you track a score, report it to the arcade shell so the player's best is remembered between visits: on every score change, call parent.postMessage({ source: "ai-arcade", type: "score", score: <number> }, "*"). It is safe to call it no matter what the parent does with it.
8. Keep it tiny: aim for under 400 lines, 60 fps, no frameworks. That 400-line target does not apply to 3D games — true 3D (a camera and perspective-projected world) or pseudo-3D (projected road/track, depth-sorted sprites) — which need their own software renderer and typically land at 800–1400 lines. The rest of this constraint still binds every game: 60 fps, no frameworks, no external assets, and no padding to reach a length.
9. Difficulty: the arcade shell passes the player's chosen difficulty as a URL query parameter. Read it with new URLSearchParams(location.search).get("difficulty") — the value is "easy", "medium", or "hard" (missing or unknown means "medium"). Make the three levels meaningfully different — speed, lives, enemy pressure, reaction time, whatever fits the genre; clicker/idle games with no losing state use starting resources and upgrade cost curves instead. Show the active level in the HUD. Without the parameter the game must be fully playable at its default (medium) tuning.

Return only the complete HTML file, no commentary.