The iOS app lets an account reach one server through several addresses, such as a home network
IP and a public name. Before it sends credentials to an alternative address it needs to know the
address leads to the same installation, so expose a public, credential-free GET /server-identity
returning a persisted UUID, and add the same optional instanceId to app-info with the
server-connection-identity feature flag.
The UUID lives in a singleton server_identity row shared by every replica, created on first use
and cached per process. An unreadable identity omits instanceId instead of failing app-info,
which clients rely on for feature detection. Existing routes and bodies are unchanged and the
web client does not call the new route; the iOS app does.
The migration uses IF NOT EXISTS because an unreleased build created the same table as 0109.
neon