HorizonCraft is a personal world builder: you chat about your life and an agent turns it into a living 3D world. Mention Tahoe and a ski chalet appears by the lake; mention Rome and a Colosseum rises under a starry sky, because it's night there. Attach a selfie and you're in the world too.
Underneath is a memory layer for long-horizon agents. The agent never sees a transcript. Every prompt is rendered from a bounded typed state: placed things with coordinates, landmarks, live conditions, and facts about you. Every build stage checkpoints atomically, so killing the agent mid-generation and restarting resumes at the exact stage. Memory changes behavior: rejected things go into a failures ledger and get regenerated differently; earlier builds become landmarks later requests can reference.
Sponsors: OpenAI gpt-5-mini interprets conversation into structured actions from state, not history, so prompts stay ~800 tokens at turn 100. Liquid LFM2 (1.2B, local via Ollama) handles fast decisions: naming, sizing, keep/drop, half a second each. Nimble fetches real weather, temperature and local time for any place you mention, driving sky and day/night. Black Forest Labs FLUX draws every object, and FLUX Kontext turns selfies into characters. fal.ai hosts Hunyuan3D for image-to-mesh. Rawtree records every decision and token count, feeding a memory panel that proves the context never grows.
