Salt Pan

Build a tiny browser game called "Salt Pan".

Game spec
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A salt pan where you harvest crystallising brine. A shallow pan of seawater evaporates under a heat that you control, and as it concentrates the brine passes through the mineral windows in order — first gypsum, then halite, then the bitter bitterns that ruin the crop. You must close the inlet and rake the crystals out while the brine sits inside the good window, and the pan tells you where it is by a live density readout and by the colour and crust forming on the surface. The trade is speed against purity: push harder with the heat and the crop arrives sooner but overshoots the window and you harvest bitter salt that sells for nothing; go gentle and the tide line comes in and floods the pan before you finish. Rake with the arrow keys or a drag across the pan, holding to gather a windrow, and a crust that is left too long cements to the floor and costs a pan. Brine depth, density and the current mineral window are all on a gauge board with the safe band marked, and the harvest pays by crop weight, purity and time. Filling past the brim or letting the pan bake dry ends the run, and the number of pans you get depends on difficulty. Salt-flat look: mirror-bright brine with a sky reflection, white crust terraces with pink halite tint, wooden rakes with iron shoes, a distant heap of harvested salt, and a wind hiss plus a crust-crack under the rake 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.