chore(workspace): scaffold net crate for QUIC transport

crates/net/Cargo.toml

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+[package]
+name = "net"
+license.workspace = true
+license-file.workspace = true
+authors.workspace = true
+edition.workspace = true
+version.workspace = true
+
+[dependencies]
+crossbeam-channel = "0.5.16"
+postcard.workspace = true
+quinn = "0.11.11"
+rcgen = "0.14.8"
+rustls = "0.23.41"
+serde.workspace = true
+thiserror.workspace = true
+tokio = { version = "1.52.3", features = ["rt-multi-thread", "macros", "net", "sync", "io-util", "time"] }
+tracing.workspace = true
+shared = { path = "../shared" }
+
+[lints]
+workspace = true

crates/net/src/codec.rs

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+// SPDX-License-Identifier: AGPL-3.0-only
+
+//! Length-prefixed `postcard` frame codec.
+//!
+//! Encodes and decodes one logical protocol message per record on a QUIC stream, using a length prefix so a reader can recover record boundaries from a byte stream. Populated in a later concept; currently a placeholder.

crates/net/src/endpoint.rs

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+// SPDX-License-Identifier: AGPL-3.0-only
+
+//! QUIC endpoint construction for client and server.
+//!
+//! Builds the `quinn` endpoints and configures ALPN and TLS 1.3 (self-signed server certificate, permissive client verifier for the initial milestone). Populated in a later concept; currently a placeholder.

crates/net/src/handshake.rs

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+// SPDX-License-Identifier: AGPL-3.0-only
+
+//! Synvael application handshake over an established QUIC connection.
+//!
+//! Drives the `ClientHello` -> `HandshakeAck` / `HandshakeReject` exchange and protocol-version verification on the control stream. Populated in a later concept; currently a placeholder.

crates/net/src/lib.rs

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+// SPDX-License-Identifier: AGPL-3.0-only
+
+//! QUIC transport, connection lifecycle, and wire framing for the Synvael client-server protocol.
+//!
+//! This crate owns the asynchronous runtime and the transport dependencies, keeping them out of the lean `shared` protocol crate. Protocol message types live in `shared`; this crate is responsible only for carrying them over the wire.
+//!
+//! The synchronous simulation loop (`server`) and windowing loop (`client`) never touch the async runtime directly. They exchange messages with the network over channels, so the async runtime stays confined to this crate.
+
+pub mod codec;
+pub mod endpoint;
+pub mod handshake;
+pub mod runtime;

crates/net/src/runtime.rs

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+// SPDX-License-Identifier: AGPL-3.0-only
+
+//! Threaded `tokio` runtime bridge between the async network and the synchronous simulation.
+//!
+//! Owns the runtime thread and the channels that carry inbound and outbound messages across the async-sync boundary, keeping the async runtime confined to this crate. Populated in a later concept; currently a placeholder.