docs: add Phase 8-2 networking status, spec, plan, and deferred items

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

docs/superpowers/specs/2026-03-25-phase8-2-networking.md

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+# Phase 8-2: Networking Foundation — Design Spec
+
+## Overview
+
+`voltex_net` crate를 신규 생성한다. UDP 소켓 래핑, 패킷 직렬화, 클라이언트-서버 연결 관리를 구현한다.
+
+## Scope
+
+- 패킷 프로토콜 (Connect, Accept, Disconnect, Ping, Pong, UserData)
+- 바이너리 직렬화/역직렬화
+- Non-blocking UDP 소켓 래퍼
+- NetServer (클라이언트 관리, broadcast)
+- NetClient (서버 연결, 핸드셰이크)
+
+## Out of Scope
+
+- 상태 동기화 (스냅샷)
+- 보간 / 예측
+- 지연 보상
+- 신뢰성 계층 (재전송, 순서 보장)
+- 암호화 / 인증
+
+## Module Structure
+
+```
+crates/voltex_net/
+├── Cargo.toml
+└── src/
+    ├── lib.rs
+    ├── packet.rs    — Packet enum, to_bytes, from_bytes
+    ├── socket.rs    — NetSocket (UdpSocket wrapper)
+    ├── server.rs    — NetServer
+    └── client.rs    — NetClient
+```
+
+## Dependencies
+
+- 없음 (std::net::UdpSocket만 사용)
+
+## Types
+
+### Packet
+
+```rust
+#[derive(Debug, Clone, PartialEq)]
+pub enum Packet {
+    Connect { client_name: String },
+    Accept { client_id: u32 },
+    Disconnect { client_id: u32 },
+    Ping { timestamp: u64 },
+    Pong { timestamp: u64 },
+    UserData { client_id: u32, data: Vec<u8> },
+}
+```
+
+### 직렬화 포맷
+
+```
+[type: u8] [payload_len: u16 LE] [reserved: u8] [payload...]
+```
+
+Type IDs: Connect=1, Accept=2, Disconnect=3, Ping=4, Pong=5, UserData=6
+
+Payload encoding:
+- Connect: name_len(u16) + name_bytes
+- Accept: client_id(u32)
+- Disconnect: client_id(u32)
+- Ping/Pong: timestamp(u64)
+- UserData: client_id(u32) + data_len(u16) + data_bytes
+
+```rust
+impl Packet {
+    pub fn to_bytes(&self) -> Vec<u8>
+    pub fn from_bytes(data: &[u8]) -> Result<Packet, String>
+}
+```
+
+### NetSocket
+
+```rust
+pub struct NetSocket {
+    socket: UdpSocket,
+}
+```
+
+- `bind(addr: &str) -> Result<Self, String>` — bind + set_nonblocking(true)
+- `send_to(&self, packet: &Packet, addr: SocketAddr) -> Result<(), String>`
+- `recv_from(&self) -> Option<(Packet, SocketAddr)>` — None if WouldBlock
+
+### ClientInfo
+
+```rust
+pub struct ClientInfo {
+    pub id: u32,
+    pub addr: SocketAddr,
+    pub name: String,
+}
+```
+
+### NetServer
+
+```rust
+pub struct NetServer {
+    socket: NetSocket,
+    clients: HashMap<u32, ClientInfo>,
+    next_id: u32,
+}
+```
+
+- `new(addr: &str) -> Result<Self, String>`
+- `poll(&mut self) -> Vec<ServerEvent>` — process incoming packets
+- `broadcast(&self, packet: &Packet)` — send to all clients
+- `send_to_client(&self, client_id: u32, packet: &Packet)`
+- `clients(&self) -> &HashMap<u32, ClientInfo>`
+- `client_count(&self) -> usize`
+
+### ServerEvent
+
+```rust
+pub enum ServerEvent {
+    ClientConnected { client_id: u32, name: String },
+    ClientDisconnected { client_id: u32 },
+    PacketReceived { client_id: u32, packet: Packet },
+}
+```
+
+### NetClient
+
+```rust
+pub struct NetClient {
+    socket: NetSocket,
+    server_addr: SocketAddr,
+    client_id: Option<u32>,
+    name: String,
+}
+```
+
+- `new(local_addr: &str, server_addr: &str, name: &str) -> Result<Self, String>`
+- `connect(&self)` — send Connect packet
+- `poll(&mut self) -> Vec<ClientEvent>` — process incoming
+- `send(&self, packet: &Packet) -> Result<(), String>`
+- `is_connected(&self) -> bool`
+- `client_id(&self) -> Option<u32>`
+- `disconnect(&self)`
+
+### ClientEvent
+
+```rust
+pub enum ClientEvent {
+    Connected { client_id: u32 },
+    Disconnected,
+    PacketReceived { packet: Packet },
+}
+```
+
+## Test Plan
+
+### packet.rs
+- Connect 라운드트립
+- Accept 라운드트립
+- Disconnect 라운드트립
+- Ping/Pong 라운드트립
+- UserData 라운드트립
+- 잘못된 바이트 → 에러
+
+### socket.rs
+- localhost 바인드
+- send + recv 라운드트립
+
+### server.rs + client.rs (통합)
+- 서버 시작 + 클라이언트 연결 → Accept 수신
+- 다수 클라이언트 연결
+- 클라이언트 Disconnect → 서버에서 제거
+- UserData 송수신