Interactive jelly Japanese island diorama with water, flora, and wildlife

[Note: the creator shared a partial prompt. Wording below is theirs.] GOAL: Build a single-file interactive WebGPU diorama called "Koi Jelly" for a "Material Studies" series: a Japanese castle stroll garden around a koi pond, cut out as a square block of clear jelly standing on a pale paper-grey table. MOTION: Plain JS + WGSL, no libraries, everything inline, no network requests. SCENE (block ~5.2 × 5.2 units, water level ~1.0): - The pond fills the front and right of the block; its cut faces show koi swimming through the jelly. - Back right: a castle bailey on sheer dry-stone walls (ishigaki) rising straight out of the water, a white multi-tiered keep (tenshu) with dark tiled roofs and upturned eaves, a stone stair down to the paths. - Back left: a five-storey pagoda on a hill and a bell tower with a big bronze bell. - Between them: a waterfall pouring off a rocky knoll through a notch with a sheer face into a plunge pool, with foam and a current pushing out into the pond; maples and azaleas on the knoll. - Left: a lawn and moss garden, a raked-gravel rock garden (karesansui), and a tea house with a veranda by the water, a red parasol (nodategasa) and red bench cloths. Stone lanterns (tōrō, yukimi-dōrō) along gravel paths, a deer-scarer (shishi-odoshi) that slowly fills, tips and knocks. - A promontory leads to a red arched drum bridge (taiko-bashi) onto the big island: a weeping cherry with long pink strands, a snow-viewing lantern, a leaning pine. - A zigzag plank bridge (yatsuhashi) crosses an iris marsh in a back cove. A crane island with tall rocks and a leaning pine; a turtle island with flat basking rocks. - ~17 cherry trees in full bloom, azaleas, pines, maples, edging stones round the pond, a pebbly pond bed with algae. WATER: a real-time shallow-water heightfield (~168² grid) with refraction, colour absorption, caustics on the bed, foam and ripples. Everything disturbs it: koi gulps, ducks, the boat, raindrops, the waterfall current. Drag on the water to stir it; drag on the ground to tilt the whole jelly block (it wobbles back). LIFE: - 16 koi in real varieties (kohaku, sanke, showa, yamabuki ogon, platinum, asagi, chagoi, tancho) with procedural patterns, cruising just under the surface and schooling loosely; little medaka. - Pairs of mandarin ducks; a kingfisher that perches and dives; a grey heron that wades, strikes and flies between spots; Japanese white-eyes flitting in the blossom. - Pond turtles that bask on rocks, slide in with a plop when startled, swim around the island and haul out again. - People strolling the paths and crossing the bridges, a monk at the bell, a boatman poling a pleasure boat. EVENTS (four main buttons): 1. Feed the koi (also Space, or tap the drum bridge): a visitor walks to the crown of the bridge and throws five handfuls of floating pellets; the koi crowd in, mouths open, and slurp every pellet (count shown). 2. Hanami: a gust shakes the cherries; hundreds of petals tumble and drift, gathering into petal rafts (hanaikada) on the water; picnic mats appear; the boat sets ou