_pe_dchan_reorder.nx

_pe_dchan_reorder.nx -- X-ROOM-DC-003 rung-3 RELIABILITY DATA PLANE (the ACTION layer the spec flagged as the emitter frontier: "seq-number arithmetic + payload reorder-buffer ... wired at integration"). COMPOSES the organ-authored FSM control core _pe_dchan_arq (states/transitions = WHEN to retransmit) with the data-plane ACTIONS (WHAT: in-order delivery under loss+reorder). dp_recv: a sliding-window reorder buffer -- buffer out-of-order seqs, deliver contiguous from base, dedup old seqs, drop out-of-window, cumulative-ack = base (next expected). This is the N-party correctness layer (a 2-peer TCP room gets order free; N>2 / late-join needs this). HONEST AUTHORSHIP (memory discipline): the FSM TABLE is organ-emitted (_pe_dchan_arq); these ACTIONS are hand-built -- a DECLARED SCAFFOLD, emitter-of-emitters back-fill OWED (X-AUT-012 class). Gate is self-validating: FSM send/ack/timeout-retransmit control + reorder/loss/dup data plane, with a neg-control (a broken pass-through would deliver out-of-order -> RED).