Caisson

Build a tiny browser game called "Caisson".

Game spec
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A brick caisson sunk through soft ground to find water. The shaft is a heavy ring of brickwork that you dig out from underneath, and it sinks under its own weight as the soil is removed from the cutting edge. Everything is about keeping it plumb: dig more under one side and that side sinks faster, so the shaft leans, and a shaft that leans past tolerance jams in the ground and cannot be righted, which ends the run. Dig by clicking or tapping a sector of the cutting edge to spoil it out, or move a cursor around the ring with the arrows and press Space; the amount you take per dig depends on how waterlogged that sector is. Water floods the shaft as you go deeper and you bail with a bucket on a windlass (hold E) to keep the working face clear, and bailing takes the time the shaft spends leaning. A plumb bob and a tilt needle show the current lean and which side is running ahead, and a depth gauge counts the rings sunk. Every ring that seats level pays, water found pays a strike bonus scaled by remaining time and bricks spared, and difficulty sets soil softness, water inflow, tolerance and depth. Digging look: a brick ring with tarred joints, wet boulder clay with rootlets, a hand windlass with a rope and bucket, a tallow lamp on a nail, a plumb bob on twine, and dripping water with a bucket creak in WebAudio.

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.