-- Latency probes are nonce-bound: the backend issues a challenge, the client
-- echoes it back with its opaque Steam location, and the backend computes RTT
-- from its own send/receive timestamps rather than trusting a client-reported
-- number.
--
-- Nothing issued that nonce before, so ProbeProvider had no expected value to
-- compare against and /v1/probes/{region} was unreachable in every real
-- binary. With no probe, queue_tickets.predicted_rtt stayed empty, and
-- domain.validCandidate hard-requires a non-empty map -- so no client-created
-- ticket could ever be selected by the matcher.
--
-- The challenge is durable rather than per-process because any control-plane
-- replica may serve the follow-up submission.
CREATE TABLE probe_challenges (
    player_id TEXT NOT NULL REFERENCES identities(player_id) ON DELETE CASCADE,
    region TEXT NOT NULL CHECK (region IN ('EU', 'NA')),
    nonce BYTEA NOT NULL,
    issued_at TIMESTAMPTZ NOT NULL,
    PRIMARY KEY (player_id, region)
);

-- Supports the expiry sweep; challenges are short-lived and single-use.
CREATE INDEX probe_challenges_issued_at ON probe_challenges (issued_at);