The Drowned Valley

The brief, in short:

Here is a design document for The Drowned Valley: a 25 to 35 minute vertical slice of an open-world action-adventure in the Zelda and Fable tradition, solo or two-player co-op. A valley's dam-keeper has vanished and the water is rising. Four pillars: the world remembers you, one map becomes many maps as the water rises, co-op changes the story rather than the headcount, and progression is new verbs rather than bigger numbers. Build a compact, playable prototype of it in Airogel as a stress test of the engine.

The agent treated the document as the spec and built a 230 metre northbound slice with 192 authored objects: the Overlook, Lowmere, the orchard with its west and east routes, the sluice house, the cliff road, three Weir chambers, a guardian, and the buried-door stinger.

• It imported one Mixamo character and six motion clips (idle, walk, run, attack, swim) and shared them between both players' avatars.
• Bridges, the village well, the sluice wheel, iron chains, the keeper's sword and the keeper's cache are generated meshes. Each one's recipe is kept so it can be regenerated.
• Water is scripted: four story-triggered states, a bounded current, wading thresholds and swimming, with the Weir chambers draining on their own timers.
• Companion selection, following, a context command and a two-handed sluice wheel that needs the companion to hold the second wheel all live in Lua. Story flags (goats, lantern, horn) change what characters say and where the goats turn up later.
• In co-op the room server runs the world and the two players must agree on the ending within ten seconds, or it waits.

It took a checkpoint of the untouched starter before changing anything, then ran scripted smoke tests of both endings through the editor's physics simulation, recorded the results as evidence files, and built 26 releases before this one. Three support tickets it filed about the sluice, the spillway and the published solo build were fixed in the engine while it worked.

The atmosphere pass (16 October, release 27). The agent scored release 26 against the design document beat by beat and found the valley silent and flat. It synthesized all 33 sounds and both music themes with a Python script, nothing recorded or licensed: zone beds, positional loops for the river, shoreline, sluice and drips, one-shots for every verb, an underwater muffle and per-space reverb, bound to the Lua scripts by a placeholder-filling tool after upload.

• Look: ACES tone mapping, valley fog, a low warm sun, bloom, ambient occlusion, fifteen point lights and fifteen particle emitters, emissive lanterns and runes, cliff faces and a far ridge with a broken watchtower.
• Verbs and combat: a dodge with a burst and a protection window, wading slowdown, and a second phase for the Weir-warden in which the middle pool refloods behind the player.
• World memory: the lantern becomes a carried light in a darker Weir, the horn is answered at the ending, and the goats turn up bleating on the high road.
• Staging: an archway so the buried door frames the boss fight, and an ending in which the door grinds open an inch, the signal fire relights and the far tower blinks back.

It verified the dodge and a full route from companion pick to the spillway ending, including the second phase, by editor simulation with zero script errors, and kept a plan-versus-build record of what the slice still lacks.