v0.6.6: WireGuard-style immediate delivery for settled single-link mode Bypasses ReorderBuffer entirely when scheduling has settled on a single active link (primary_link_mode/follow_peer_primary), matching WireGuard's own single-path delivery architecture, instead of merely shrinking the reorder-buffer window (v0.6.5, verified in production to not help). Includes a Critical fix from independent review: peer_primary_link is now correctly reset on session changes in the bypass branch too, closing a path where it could have latched forever across rekeys under follow_peer_primary.