Steel Rain 3D

Build a tiny browser game called "Steel Rain 3D".

Game spec
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A first-person wave-survival shooter in one self-contained file, rendered with raw WebGL (no libraries): a lit flat-shaded scene of a walled 44x44 arena with a neon floor grid and nine cover pillars, drawn from an eye camera with pointer-lock mouse look (drag fallback) and WASD/arrow movement with circle-vs-AABB collision. Click or Space fires a hitscan rifle (ray-sphere vs enemies, ray-AABB occlusion by pillars) with a glowing tracer, muzzle flash and recoil; two 35-damage shots kill either enemy type. Orange octahedron rams charge the player (contact damage with knockback and a per-enemy cooldown); purple shooters hover at range, strafe, telegraph with a glow and lob dodgeable magenta plasma bolts that die on pillars, walls and the ground. Waves spawn from random edges on a difficulty-scaled timer and count; clearing a wave pays wave x 250 with a banner, and every kill has a chance to drop a green hull cell worth +25. Red damage flash, 0.6 s i-frames, particle debris with gravity and bounce, WebAudio for shots, hits, explosions, bolts, pickups and wave fanfares, HUD plates for hull bar, score, wave and difficulty tag, and score posted via parent.postMessage({source:'ai-arcade',type:'score',score}). Zero hull ends the run with a score card, localStorage best and re-deploy button. ?difficulty=easy|medium|hard (default medium) scales hull, spawn pressure, enemy speed, bolt speed/damage, fire rate and drop rate; on-screen move stick, look-drag and FIRE button appear under pointer:coarse.

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.