MGASA-2026-0489

This update fixes security issues:

• Only accept a CONFLUX_LINK cell on a plain OR circuit, and refuse to turn a (pending) conflux leg into an introduction or rendezvous point. Previously a client could link a rendezvous-point circuit into a conflux set and then, with a forged sequence number in the LINK cell, make the relay tear the set down from inside the rendezvous splice, triggering a fatal assertion in assert_circuit_ok(). Also reject a LINK/LINKED cell whose last_seqno_recv is above what we ever sent on the set.
• Correctly copy the MiddleOnly flag from routerstatuses to node objects. Without this fix, the MiddleOnly flag was ignored on non-authorities, and clients could use MiddleOnly relays for inappropriate roles in onion service circuits. Tracked as TROVE-2026-067.
• Treat a router descriptor as expired if any of its family certificates has expired. Previously, we incorrectly ignored the expiration time of the family certificate. Tracked as TROVE-2026-062.