feat: v2 Phase 1 — foundation, proto schemas, RPC framework, SDK skeleton

New workspace structure with 9 crates. Adds:

- proto/qpq/v1/*.proto: 11 protobuf schemas covering all 33 RPC methods
- quicproquo-proto: dual codegen (capnp legacy + prost v2)
- quicproquo-rpc: QUIC RPC framework (framing, server, client, middleware)
- quicproquo-sdk: client SDK (QpqClient, events, conversation store)
- quicproquo-server/domain/: protocol-agnostic domain types and services
- justfile: build commands

Wire format: [method_id:u16][req_id:u32][len:u32][protobuf] per QUIC stream.
All 151 existing tests pass. Backward compatible with v1 capnp code.

crates/quicproquo-proto/build.rs

@@ -1,51 +1,30 @@
 //! Build script for quicproquo-proto.
 //!
-//! Invokes the `capnp` compiler to generate Rust types from `.capnp` schemas
-//! located in the workspace-root `schemas/` directory.
-//!
-//! # Prerequisites
-//!
-//! The `capnp` CLI must be installed and on `PATH`.
-//!
-//! Debian/Ubuntu:  apt-get install capnproto
-//! macOS:          brew install capnp
-//! Docker:         see docker/Dockerfile
+//! Runs two code generators:
+//! 1. Cap'n Proto (v1 legacy) — from `schemas/*.capnp`
+//! 2. Protobuf/prost (v2) — from `proto/qpq/v1/*.proto`
 
 use std::{env, path::PathBuf};
 
 fn main() {
-    let manifest_dir =
-        PathBuf::from(env::var("CARGO_MANIFEST_DIR").expect("CARGO_MANIFEST_DIR not set by Cargo"));
+    // Vendor protoc from protobuf-src so the build doesn't require system protoc.
+    std::env::set_var("PROTOC", protobuf_src::protoc());
 
-    // Workspace root is two levels above this crate (quicproquo/crates/quicproquo-proto).
+    let manifest_dir =
+        PathBuf::from(env::var("CARGO_MANIFEST_DIR").expect("CARGO_MANIFEST_DIR"));
     let workspace_root = manifest_dir
         .join("../..")
         .canonicalize()
-        .expect("could not canonicalize workspace root path");
+        .expect("canonicalize workspace root");
 
+    // ── v1: Cap'n Proto codegen ──────────────────────────────────────────────
     let schemas_dir = workspace_root.join("schemas");
 
-    // Re-run this build script whenever any schema file changes.
-    println!(
-        "cargo:rerun-if-changed={}",
-        schemas_dir.join("auth.capnp").display()
-    );
-    println!(
-        "cargo:rerun-if-changed={}",
-        schemas_dir.join("delivery.capnp").display()
-    );
-    println!(
-        "cargo:rerun-if-changed={}",
-        schemas_dir.join("node.capnp").display()
-    );
-    println!(
-        "cargo:rerun-if-changed={}",
-        schemas_dir.join("federation.capnp").display()
-    );
+    for schema in &["auth.capnp", "delivery.capnp", "node.capnp", "federation.capnp"] {
+        println!("cargo:rerun-if-changed={}", schemas_dir.join(schema).display());
+    }
 
     capnpc::CompilerCommand::new()
-        // Treat `schemas/` as the include root so that inter-schema imports
-        // resolve correctly.
         .src_prefix(&schemas_dir)
         .file(schemas_dir.join("auth.capnp"))
         .file(schemas_dir.join("delivery.capnp"))
@@ -56,4 +35,32 @@ fn main() {
             "Cap'n Proto schema compilation failed. \
              Is `capnp` installed? (apt-get install capnproto / brew install capnp)",
         );
+
+    // ── v2: Protobuf/prost codegen ───────────────────────────────────────────
+    let proto_dir = workspace_root.join("proto");
+
+    let proto_files = [
+        "qpq/v1/common.proto",
+        "qpq/v1/auth.proto",
+        "qpq/v1/delivery.proto",
+        "qpq/v1/keys.proto",
+        "qpq/v1/channel.proto",
+        "qpq/v1/user.proto",
+        "qpq/v1/blob.proto",
+        "qpq/v1/device.proto",
+        "qpq/v1/p2p.proto",
+        "qpq/v1/federation.proto",
+        "qpq/v1/push.proto",
+    ];
+
+    let full_paths: Vec<PathBuf> = proto_files.iter().map(|f| proto_dir.join(f)).collect();
+
+    for path in &full_paths {
+        println!("cargo:rerun-if-changed={}", path.display());
+    }
+
+    prost_build::Config::new()
+        .out_dir(PathBuf::from(env::var("OUT_DIR").expect("OUT_DIR")))
+        .compile_protos(&full_paths, &[&proto_dir])
+        .expect("prost compile_protos failed");
 }