Multiplayer replication rooms and networked motion

The recipe

1. Per-entity replication: attach NetworkProfileComponent { "type":"NetworkProfileComponent", "interpolation":"responsive", "interestRadius": 60, "alwaysRelevant": false }. interpolation is:
   • responsive: hugs the newest server sample, no gap-bridging (projectiles, snappy pickups).
   • smooth: doubles the interpolation buffer for fluid slow movers (platforms, doors).
   • default: the tick-derived baseline.
2. Visibility controls on the same component: ownerOnly: true withholds the entity from every player except its owner; hidden: true withholds it from everyone; alwaysRelevant: true and interestRadius shape whose snapshot it enters.
3. Game topology: set the room and queue blueprint with project_set_multiplayer_blueprint (game.multiplayer_blueprint.set, AI name set_game_multiplayer_blueprint). The definition carries roomTemplates (each with key, joinPolicy, maxPlayers) and queues (each with key, mode, minParticipants, maxParticipants, roomTemplateKey).
4. You do not have to configure anything to be multiplayer: an unconfigured game resolves to a default of one public room (maxPlayers 16) plus one open queue, so the runtime never lacks a blueprint.

Pitfalls

• NetworkProfileComponent is presentation intent for replicated motion; it does not itself move the entity. It reads into the interpolation buffer (no second mover).
• Netcode is client-authoritative single-writer over relays; the server does not re-simulate. Use server_authoritative input prediction (see input-mapping-actions-bindings) for verbs that must resist cheating.
• ownerOnly withholds the WHOLE entity from non-owners, not just a field; a first-person viewmodel is a good ownerOnly candidate.
• The blueprint mutation carries the full definition (settings-panel edits send the whole object); send a complete roomTemplates+queues shape, not a diff.

Verify

• engine_get_component_schema on NetworkProfileComponent for the interpolation enum and the visibility flags.
• project_get_graph_snapshot and the game record to confirm the blueprint set.
• simulation_run (qa.run.start) for a multi-participant admission check.