DRIFTWING

Build a complete, self-contained browser game in a SINGLE index.html file. No build step, no external assets, libraries only via CDN importmap. Use three.js (latest) with WebGPURenderer and automatic WebGL fallback.
THE GAME: "DRIFTWING", an ambient infinite-flight exploration game. You pilot a low-poly glider over an endless procedural world. No fail state, no fuel, no enemies. The fantasy: a golden-hour flight that never has to end, with an AI copilot riding shotgun.
FLIGHT MODEL (arcade with soul):
- Mouse steers pitch and roll (WASD/arrows also work), scroll or W/S for throttle, space for a gentle boost on cooldown
- Banking turns: rolling into a turn induces natural yaw; speed bleeds in climbs and builds in dives
- Soft stall: below minimum speed the nose eases down, never a tumble
- Chase cam with smooth lag that banks with the plane, FOV stretches with speed, subtle shake at max velocity
- Touch support: virtual joystick plus throttle slider
- Double-tap A or D triggers a smooth canned barrel roll
INFINITE TERRAIN (the engineering core):
- Chunked heightmap terrain from seeded simplex noise, multiple octaves, fully deterministic from a seed shown in the UI so worlds are shareable
- Biomes blended by temperature/moisture noise: snow peaks, pine valleys, dunes, archipelago ocean, flower meadows; vertex-colored, flat-shaded low-poly
- Chunk generation in a Web Worker with transferable buffers, ring LOD (high detail near, low far), pooled and recycled chunk meshes, zero frame hitches while streaming
- Stitched LOD edges or skirts so there are never visible cracks
- Procedural landmarks every few km: stone arches, monolith circles, a lighthouse on a lone island, drifting hot air balloons; discoveries log to a journal
LIVING ATMOSPHERE:
- Day/night cycle (6 min loop, settable): sun, moon, star field, dawn/dusk gradients, aurora over snow biomes at night
- Sky: gradient dome with a sun disc and cheap radial god rays near the horizon; fog color always matches the sky
- Clouds: instanced soft puffs in a slow-drifting layer casting faint shadow blobs
- Water: animated vertex waves, sun glint streak, foam band at shorelines
- Boid bird flocks that scatter when you dive through them
- Wingtip contrails when banking hard, wind streak lines at speed
THE COPILOT (critical architecture):
- class Copilot { async respond(flightState, transcript) -> { speech, action } }
- Default brain = local keyword grammar via the Web Speech API: "where am I", "find mountains / ocean / desert", "set waypoint", "autopilot on/off", "make it night / dawn", "barrel roll", "ring course"
- Executable actions: place a glowing waypoint beacon, autopilot to a heading, change time of day, spawn a ring course, describe current biome and altitude
- RemoteCopilot: POSTs { flightState, transcript } to a configurable endpoint (default http://localhost:3000/copilot), expects { speech, action } back, falls back to the local grammar after an 800ms timeout
- Copilot answers via speechSynthesis plus a subtitle line in the glass UI; mic toggle with a pulsing listening indicator; every command also reachable by keyboard/UI so voice is never required
GENTLE OBJECTIVES (optional, never nagging):
- Ring courses on request: fly-through rings with chime feedback, time and best streak
- Discovery journal: biomes visited, landmarks found, distance flown, max altitude
- Photo mode: P pauses, frees the camera, hides UI, adds letterbox and a screenshot button
VISUAL QUALITY BAR (this is the entire point):
- Cohesive 6-color palette per biome, flat shading, soft sun shadows
- Post stack: subtle bloom, vignette, warm color grade, light film grain
- Golden-hour default start: long shadows, warm fog, the screenshot moment inside the first 5 seconds
- Minimal glass UI: altitude, speed, compass strip, waypoint arrow, world seed, mic toggle; auto-hides after 3 seconds of stillness
PERFORMANCE:
- 60fps target on desktop: frustum culling, instancing for trees/rocks/clouds, worker-side terrain, auto-degrade view distance before frame drops
- Guard against: LOD cracks, falling through unloaded chunks (clamp altitude to terrain height plus epsilon), NaN attitude, worker backlog, tab-blur dt spikes
POLISH RULES:
- Every listed system must actually function, zero placeholders
- Opens already airborne at golden hour with a 1-second fade, no menu wall, no console errors

This is part of the prompt; the creator didn't share all of it.

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