Declares that two markets on two different venues are the same real-world contract, making them routable together by GET /orders/route-quote, POST /orders/route-buy and POST /orders/route-close. Two-step by design. confirm: false (the default) returns a verified preview and writes nothing. Show the user the resolved pairing, then call again with confirm: true AND the preview's verification_fingerprint as fingerprint. The confirm re-resolves against fresh metadata and requires the result to fingerprint-match what was reviewed, so index drift between the two calls becomes a 409 ("review the pairing again") rather than a silently different link. You attest; the server verifies. Both legs are resolved against indexed market metadata and the link is REFUSED unless the venues' yes/no outcome labels pair exactly (case-insensitive). Outcome inversion is the one catastrophic failure mode here, so it is gated deterministically rather than by the user's click — a Yes/No vs Trump/Harris pair may well be the same market, but the mapping is not machine-provable and is refused rather than guessed. Scope of a created link. Links are approved but USER-SCOPED: routable only by their creator, so a bad self-link's blast radius is the creator's own wallet. Capped at 25 links per user, enforced inside the insert transaction so concurrent confirms cannot overshoot it. Expiry gaps and resolution-source divergence come back as warnings, not errors — for a self-scoped link they are the creator's risk to accept. Rate limited at 15 requests/minute per user (MARKET_LINK_RATE_LIMIT_PER_MIN), fail-closed. Previews count: every call costs two indexed-metadata lookups plus duplicate checks, and the 25-link cap only bounds completed inserts.

Error shape. This endpoint returns {"message": "..."} — NOT the {"error": ...} used everywhere else on this service, and with no code field. See OrderMarketLinkErrorResponse. Auth. Requires authentication and the mutation gate (API-key triple, X-Service-Token, or CSRF token). API keys and delegations need trade:execute, previews included; a created link steers the creator's later routed orders.