---
id: multiplayer
title: "Multiplayer — replication, netcode, the console"
status: provisional
source_sections: "PROGRESS_LOG.md §7 (Phase 7), §8 (P6); docs/HARD_PROBLEMS.md (P6)"
related_topics: [wintesla-port, combat-damage, locomotion, decomp-reference]
key_terms: [master, replicant, EGG, dead-reckon]
open_questions:
  - "Cross-pod combat (damage to a replicant's master); replicant gait; pod-LAN config"
---

# Multiplayer

Pod-to-pod networked play. The hard infrastructure exists (WinTesla replaced DOS `NETNUB` with a
WinSock2 TCP stack); the work is integrating + smoke-testing it for BT. Full detail:
`docs/PROGRESS_LOG.md §7, §8`; the problem writeup: `docs/HARD_PROBLEMS.md` (P6).

## The stack (already reconstructed)
- WinTesla replaced `NETNUB` with a **3446-line WinSock2 TCP** reimplementation (`MUNGA_L4/L4NET.CPP`,
  `SOCK_STREAM`/ReliableMode, zero SOCK_DGRAM); the master/replicant distributed-sim core
  (InterestManager/Entity/HostManager) is complete. So MP = integrate + smoke-test that stack (gated
  on P3 locomotion + P5 entity lifecycle + subsystem WAVEs). The rumored `L4NET.CPP:1853` send-size
  bug is DEAD CODE (`#if MESSAGE_BUFFERING`==0). [T2]

## Master / replicant model
- **[[master]]** = a locally-simulated entity (your mech + dummies); drives itself + EMITS update records.
- **[[replicant]]** = a peer's mech, a local proxy; DeadReckons toward the master's replicated position.
  MUST `SetValidFlag()` at creation or every message defers forever ([[reconstruction-gotchas]] §9).

## How a session forms
`-net <port>` = networked mode (the pod listens on <port> for a CONSOLE, boots ConsoleOnly; game mesh
= <port>+1). Solo (no `-net`) never touches WinSock. The mission egg's `[pilots]` section IS the
roster (`pilot=ip[:port]` + a per-address page); each pod self-identifies by local-IP+game-port,
connects to earlier pilots, listens for later ones — a deterministic full mesh; the mission loads when
all connect. The **CONSOLE** (operator station — ABSENT from every archive) delivers the egg as chunked
`ReceiveEggFileMessage` packets + the LAUNCH `RunMissionMessage`; **`tools/btconsole.py` is our console
emulator** (⚠ `NotationFile::ReadText` expects NUL-SEPARATED lines). [T2]

## Verified milestones (one box, two instances)
- **P6 smoke test:** two instances share a world — console egg → TCP mesh → synchronized start →
  bidirectional entity replication (each renders its own mech + the peer's REPLICANT), 0 crashes.
- **Movement replication:** A's mech WALKS on B's screen (the replicant tracks the master to ~1.5u via
  dead-reckoning). The authentic mission-start ladder runs (CreatingMission→…→RunningMission via the
  console LAUNCH). SIX bugs fixed to get here (dead-reckoner install, replicant-motion DeadReckon,
  master emission threshold, emission gated on RunningMission, the console-must-LAUNCH fact, replicant
  validity). [T2]
- **Wire-format bug class found+fixed:** MakeMessages replicate RAW over TCP, so string payload must be
  INLINE (`char[N]` at the binary offsets), not a `const char*` pointer (garbage cross-pod). Check
  EVERY MakeMessage for pointer payloads. [T2]

## Debug tooling (`BT_NET_TRACE`, permanent)
`[net-tx]/[net-rx]` (L4NET), `[net-upd]` (update lookup), `[upd-repl]`, `[ent-exec]` (state ladder).
Per-instance: `BT_LOG=<file>` + `BT_AFFINITY=<mask>` (CPU pin). Update stream ≈ 60 Hz × 144-byte
records per moving master. [T2]

## Remaining (P6 phase 4 / Phase 7)
Cross-pod COMBAT (target a replicant + route damage to the owning master — Entity::Dispatch already
reroutes); interactive 2-window driving; replicant GAIT animation (derive from replicated velocity);
the pod-LAN config (real IPs, bare-IP pilot entries). See [[open-questions]]. [T3]

## Key Relationships
- Base: [[wintesla-port]] (L4NET). Depends on: [[locomotion]] (update writer), [[combat-damage]]
  (entity lifecycle). Detail: `docs/HARD_PROBLEMS.md` (P6).
