DL-331
SINGLE-INSTANCE is a transitional deployment constraint for the delivery cutover (OQ-4, design-critic HIGH): the cutover moves the delivery TRIGGER cross-instance (durable queue-group single-claim) but the dispatch plane it feeds — SessionForAccount/LiveAgentSessions, the held registry, settle edges, per-session gates — is instance-local hub RAM, so a two-instance deploy breaks hold/settle for a message claimed by the instance not hosting the author’s session (immediate fire from partial mid-turn blocks, late-block mention loss, undelivered settled suffix). A single Server is assumed until the parent record’s durable session bindings land (parent T4, sequenced after this cutover); this record’s two-instance integration proof is scoped to fabric TRANSPORT claim semantics only, not multi-instance delivery correctness
Status: Active (Matt, 2026-09-05)