Core Drop

Build a tiny browser game called "Core Drop".

Game spec
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A Blockout-style puzzle rendered as real 3D: a pinhole camera over perspective-projected cube faces, depth-sorted far to near, fixed corner eye looking down a 5x5 shaft. The shaft starts filled to N layers and the level is done when the layer counter — one per rank — hits zero. Pieces are two-layer 3D tetrominoes: R/Z rotate in plane, F swaps the two layers, arrows slide over the pit, Space soft-drops, Enter hard-drops. THE PROMISE: one fill array and one projection — the render pass draws the cells the simulation holds, and the yellow ghost outline is produced by the SAME landingZ() function the hard drop consumes, so the game cannot advertise a landing spot the drop logic then refuses. Hanging pieces (Blockout's rest-as-a-unit rule, a piece over a groove freezes mid-air) can leave filled cells above the naive rest height, which is why ghost and drop share one landing function that walks down until the piece actually fits. A rank complete at level start would clear on the first lock for free, so every start layer gets a punched permutation diagonal — one hole in every x-rank and every y-rank — plus scatter holes, and a guard loop refuses to emit any rank that starts full. Difficulty scales start layers (6/9/12), drop interval and the per-level ramp. Score for cells locked, rows squared times level times a combo multiplier, clear bonus per level. Keyboard plus on-screen pad; score reported via postMessage; audio synthesised in-file; no external requests.

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.