feat(rpc): extract native agntcy-slim-rpc crate from the FFI bindings

SlimRPC (the gRPC-like RPC framework over SLIM) was implemented only inside
the UniFFI bindings crate (agntcy/slim-bindings), forcing every Rust consumer
(a2a-slimrpc, and transitively SHADI) to depend on the FFI shim to speak
SlimRPC. Move the native engine into this repo as agntcy-slim-rpc.

Decoupling from the FFI crate: strip 37 UniFFI annotations; provide a
self-contained runtime module for the blocking convenience wrappers; use native
App<AuthProvider, AuthVerifier> / ProtoName instead of the FFI wrapper types;
drop the Server::new convenience constructors that derived the notification
receiver from the App wrapper (native entry point is
new_with_shared_rx_and_connection). See crates/rpc/DESIGN.md.

Follow-ups (separate PRs): rewire slim-bindings' slimrpc to wrap this crate;
repoint a2a-slimrpc onto it.

Signed-off-by: Luca Muscariello <muscariello@ieee.org>

Author: muscariello

Cargo.toml

@@ -10,6 +10,7 @@ members = [
     "crates/examples",
     "crates/mls",
     "crates/proto",
+    "crates/rpc",
     "crates/service",
     "crates/session",
     "crates/signal",
@@ -46,6 +47,7 @@ agntcy-slim-controller = { path = "crates/controller", version = "0.10.0" }
 agntcy-slim-datapath = { path = "crates/datapath", version = "0.16.1" }
 agntcy-slim-mls = { path = "crates/mls", version = "0.2.1" }
 agntcy-slim-proto = { path = "crates/proto", version = "0.2.0" }
+agntcy-slim-rpc = { path = "crates/rpc", version = "0.1.0" }
 agntcy-slim-service = { path = "crates/service", version = "0.11.0", default-features = false }
 agntcy-slim-session = { path = "crates/session", version = "0.5.0" }
 agntcy-slim-signal = { path = "crates/signal", version = "0.1.10" }

crates/rpc/Cargo.toml

@@ -0,0 +1,30 @@
+# Copyright AGNTCY Contributors (https://github.com/agntcy)
+# SPDX-License-Identifier: Apache-2.0
+
+[package]
+name = "agntcy-slim-rpc"
+edition = { workspace = true }
+license = { workspace = true }
+version = "0.1.0"
+description = "SlimRPC: a gRPC-like RPC framework over SLIM (native Rust)."
+
+[lib]
+name = "slim_rpc"
+
+[dependencies]
+agntcy-slim-auth = { workspace = true }
+agntcy-slim-datapath = { workspace = true }
+agntcy-slim-service = { workspace = true, features = ["session"] }
+agntcy-slim-session = { workspace = true }
+async-stream = { workspace = true }
+async-trait = { workspace = true }
+display-error-chain = { workspace = true }
+drain = { workspace = true }
+futures = { workspace = true }
+futures-timer = { workspace = true }
+parking_lot = { workspace = true }
+thiserror = { workspace = true }
+tokio = { workspace = true }
+tokio-stream = { workspace = true }
+tracing = { workspace = true }
+uuid = { workspace = true }

crates/rpc/DESIGN.md

@@ -0,0 +1,31 @@
+# agntcy-slim-rpc — design note
+
+## Why this crate exists
+
+SlimRPC (the gRPC-like RPC framework over SLIM) was implemented **only inside the
+UniFFI bindings repo** (`agntcy/slim-bindings`, `rust/src/slimrpc*`). That crate
+is the FFI adapter for foreign languages (Go/Swift/Kotlin). Because the RPC engine
+lived there, every **Rust** consumer — `a2a-slimrpc`, and transitively SHADI — was
+forced to depend on the UniFFI shim just to speak SlimRPC.
+
+This crate moves the **native Rust engine** into `agntcy/slim` where it belongs.
+`slim-bindings` becomes a thin UniFFI wrapper over it (follow-up, separate repo).
+
+## What was extracted
+
+The `slimrpc.rs` module + `slimrpc/` submodules (`channel`, `server`, `context`,
+`error`, `codec`, `rpc_session`, `session_wrapper`, `handler_traits`,
+`stream_types`) — ~5,500 LOC. The engine already worked directly on native types
+(`slim_service::app::App`, `slim_datapath::api::ProtoName`, `slim_session::*`).
+
+## Decoupling from the FFI crate
+
+- **UniFFI removed** — 37 annotations (`#[uniffi::export]`, `uniffi::Object/Record/Enum/Error`, …) stripped. The FFI surface belongs in `slim-bindings`.
+- **`get_runtime()`** — was a global in the bindings crate; now a self-contained `runtime` module here (for the blocking convenience wrappers; async callers use the `*_async` methods).
+- **`crate::App` / `crate::Name`** — the bindings' FFI wrapper types are replaced with the native `App<AuthProvider, AuthVerifier>` and `ProtoName`.
+- **`Server::new` / `new_with_connection`** — dropped. They derived the notification receiver from the App *wrapper* (`app.notification_receiver()`), which native `App` doesn't expose. The native entry point is `Server::new_with_shared_rx_and_connection` (explicit rx). The convenience wrappers move to `slim-bindings`.
+
+## Follow-ups (separate PRs)
+
+1. `agntcy/slim-bindings`: replace its `slimrpc` module with a thin UniFFI wrapper that depends on `agntcy-slim-rpc`.
+2. `a2aproject/a2a-rs`: repoint `a2a-slimrpc` off `slim_bindings` onto `agntcy-slim-rpc` + native `App`/`Name`.