One daemon writes the store

• Context: several processes writing one SQLite file need two lock disciplines and still race, and a lock held across a network call stalls every other writer.
• Decision: only the daemon opens the store as its writer, and store migrate and store restore under the store’s lock with the daemon stopped. Other processes go through the daemon’s API, or read the store with sqlite.OpenReadOnly when the daemon is down.
• Consequence: one transaction is the unit of consistency; clients fail when the daemon is down instead of writing around it.
• Enforced by: TestOnlyServeWritesTheStore, TestOnlyTheStoreTouchesSQL. See The daemon and its clients.