What problem does it solve? Multiplayer games ship with desyncs, item duplication, and cheat vulnerabilities when state ownership is undefined. This Skill provides a decision framework and concrete GDScript patterns for deciding which state the host owns, how clients request changes, and how the host validates and broadcasts updates in Summer Engine. ## Core Features & Use Cases - State ownership decision matrix: Apply the question "if a malicious client lies about this, does it break the game?" to every state field, with a canonical table covering health, inventory, position, cosmetics, and more. - Manager pattern with four RPC flavors: Build one autoload Manager per state domain with host-only mutators, validated client request handlers, authority broadcasts, and targeted rpc_id query/response for late-join state replay. - Validation and anti-cheat guidance: Seven prioritized validators (authority, existence, resource, range, line-of-sight, cooldown, magnitude) plus float-epsilon handling and silent-drop policy. - Use Case: When building a 3D action multiplayer game, use this Skill to create HealthManager, InventoryManager, and CooldownManager autoloads so clients send intent RPCs and the host validates range, cooldowns, and line-of-sight before applying damage. ## Quick Start Ask the agent to design the multiplayer state layer for your game by listing every state field and creating one host-authoritative Manager autoload per domain with validation and late-join sync.
