Deep Dive 3D

Build a tiny browser game called "Deep Dive 3D".

Game spec
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A first-person WebGL cave dive, hand-written shaders and matrices, no libraries. The tunnel is procedurally tumbled from a seeded random walk (mulberry32, reseeded per dive, pinnable via ?seed=) with rotation-minimising frames and noisy radius bumps over a radius floor that keeps every segment passable, drawn as one indexed triangle mesh (drawElements) with depth-tinted rock. Darkness is the core mechanic: a dim headlamp cone plus expanding sonar ping rings (up to 8 simultaneous, in a uniform array) are the only real lighting, with distance fog tuned per difficulty. Manage an air meter that drains faster when boosting (budgeted so a clean no-pickup dive reaches the goal on every level) and a hull meter where wall contact damages by impact speed, so a slow scrape warns instead of instantly killing; amber samples score points, cyan air pockets refill you, and the green extraction marker at ~1.6 km ends the dive. WASD/arrows plus mouse look (pointer lock with drag fallback), Space to ping, Shift to boost, the active difficulty shown in the HUD, and an on-screen D-pad under pointer:coarse. Score is samples plus metres dived plus a surface bonus weighted by leftover air; difficulty scales air capacity, drain, tunnel radius, fog density, collision damage and points per sample.

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.