feat(agent): bind transport S-MCP — outils idea_* vivants de bout en bout (M5a-e) — §14.3.1

Dernier kilomètre de l'orchestration native : une CLI MCP réellement lancée
joint le serveur MCP du projet et ses outils idea_* aboutissent au vrai dispatch.

- M5a endpoint loopback par projet (interprocess UDS/named pipe, source unique
  mcp_endpoint, cleanup au close) — zéro port réseau, AppImage/SSH-safe.
- M5b sous-commande `idea mcp-server` : pont stdio↔loopback headless (avant init
  Tauri), handshake {"project","requester"}, endpoint-absent borné, EOF propre.
- M5c McpServerHandle boucle accept + serve_peer par pair ; requester réel
  propagé jusqu'à OrchestratorRequestProcessed (fin du "mcp" figé) ; isolation
  des pairs ; terminaison propre.
- M5d apply_mcp_config écrit la déclaration réelle (current_exe + --endpoint
  mcp_endpoint + --project simple-uuid + --requester) ; McpRuntime injecté comme
  donnée (application ne dépend pas de app-tauri).
- M5e smoke e2e sur vrai loopback : list/ask inline, cible PTY → erreur typée,
  JSON malformé → pas de panic, requester propagé.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

crates/app-tauri/src/mcp_endpoint.rs

@@ -0,0 +1,173 @@
+//! Per-project loopback **endpoint** for the IdeA MCP transport (M5a).
+//!
+//! ## Where this sits in the bind (cadrage v5 §1, §2)
+//!
+//! The S-MCP transport is **stdio-spawn**: an MCP CLI (Claude Code, Codex)
+//! reads a `{command,args}` declaration and *spawns* a thin `idea mcp-server`
+//! bridge. That bridge talks JSON-RPC on its stdin/stdout to the CLI and relays
+//! every line, over a **local loopback**, to the IdeA (Tauri) process where the
+//! real [`OrchestratorService`](application::OrchestratorService) lives. The
+//! loopback is a **Unix domain socket** (Linux/macOS) or a **Windows named
+//! pipe** — never a network port, so it stays AppImage- and SSH-remote-safe and
+//! needs no firewall/permission.
+//!
+//! This module owns the **single source of truth** for that loopback address:
+//! [`mcp_endpoint`]. It is deterministic per [`ProjectId`] and is called by
+//! **both** sides of the contract (cadrage §2):
+//! - the side that *listens* — [`ensure_mcp_server`](crate::state::AppState::ensure_mcp_server),
+//!   which binds the listener at project-open and tears it down at close (M5a);
+//! - the side that *writes the CLI declaration* — `apply_mcp_config` (M5d),
+//!   which must point the spawned bridge at the **exact** same address.
+//!
+//! Keeping the derivation here (not duplicated on each side) is what makes the
+//! M1↔M3 coherence test possible.
+//!
+//! ## Transport crate choice — `interprocess`
+//!
+//! We use the [`interprocess`] crate's *local socket* abstraction rather than
+//! `tokio::net::{UnixListener, windows::named_pipe}` directly, because:
+//! - **One cross-OS API** for UDS (Unix) and named pipes (Windows): a single
+//!   `accept` loop in M5c, no divergent `cfg` branches with two transport types.
+//! - The workspace `tokio` is built **without** the `net` feature; pulling
+//!   `interprocess` (with its `tokio` feature) into *only* this crate avoids
+//!   widening tokio's surface workspace-wide.
+//! - On Unix its listener carries a *reclaim guard* that **unlinks the socket
+//!   file on drop** — so closing a project (dropping the handle) cleans the
+//!   filesystem with no leak, satisfying M5a's teardown requirement for free.
+//!
+//! We deliberately bind a **filesystem-path** socket on Unix (under a per-user
+//! runtime dir) rather than an abstract/namespaced one, so that the existence of
+//! the endpoint is observable as a real path (testable) and cleaned up on close.
+
+use std::path::PathBuf;
+
+use domain::ProjectId;
+
+/// The loopback address of a project's MCP endpoint — the value [`mcp_endpoint`]
+/// returns. Deterministic per [`ProjectId`]; the single source of truth shared by
+/// the listener (M5a/M3) and the CLI-declaration writer (M5d).
+///
+/// On Unix it is a **filesystem path** to a Unix-domain socket (the file is what
+/// gets bound and, on close, unlinked). On Windows it is a **named pipe** path of
+/// the form `\\.\pipe\idea-mcp-<id>`. The [`as_cli_arg`](Self::as_cli_arg) form is
+/// the exact string handed to the spawned bridge via `--endpoint`.
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct McpEndpoint {
+    /// The platform-native address string (UDS path / named-pipe path).
+    addr: String,
+}
+
+impl McpEndpoint {
+    /// The address as the bridge expects it on the command line (`--endpoint`).
+    /// Identical string on both sides of the contract (cadrage §2).
+    #[must_use]
+    pub fn as_cli_arg(&self) -> &str {
+        &self.addr
+    }
+
+    /// The Unix socket **file path**, when this endpoint is a filesystem-path UDS.
+    /// Used by the listener to ensure the parent runtime dir exists and by tests to
+    /// assert creation/cleanup. `None` on platforms whose address is not a path
+    /// (Windows named pipes have no filesystem entry to manage).
+    #[must_use]
+    pub fn socket_path(&self) -> Option<PathBuf> {
+        #[cfg(unix)]
+        {
+            Some(PathBuf::from(&self.addr))
+        }
+        #[cfg(not(unix))]
+        {
+            None
+        }
+    }
+}
+
+/// The directory under which per-project Unix sockets live, derived from the
+/// per-user runtime dir (`$XDG_RUNTIME_DIR`, falling back to `$TMPDIR`, then
+/// `/tmp`). Kept short so the full socket path stays well under the ~108-byte
+/// `sockaddr_un` limit (`/run/user/<uid>/idea-mcp/<32 hex>.sock` ≈ 50 bytes).
+#[cfg(unix)]
+fn unix_runtime_dir() -> PathBuf {
+    let base = std::env::var_os("XDG_RUNTIME_DIR")
+        .map(PathBuf::from)
+        .or_else(|| std::env::var_os("TMPDIR").map(PathBuf::from))
+        .unwrap_or_else(|| PathBuf::from("/tmp"));
+    base.join("idea-mcp")
+}
+
+/// **Single source of truth.** Computes the deterministic loopback endpoint of a
+/// project's MCP transport from its [`ProjectId`].
+///
+/// Same input ⇒ same output (stable across calls and processes); distinct projects
+/// ⇒ distinct endpoints (the id's 32-hex *simple* form is unique and collision-free
+/// by construction). No network port is ever used.
+///
+/// - **Unix**: `<runtime-dir>/idea-mcp/<id>.sock` — a UDS file path.
+/// - **Windows**: `\\.\pipe\idea-mcp-<id>` — a named pipe.
+///
+/// where `<id>` is the project UUID in hyphen-free hex (`simple`) form.
+#[must_use]
+pub fn mcp_endpoint(project_id: &ProjectId) -> McpEndpoint {
+    // Hyphen-free, lowercase, fixed-width (32 chars): safe in both a filename and
+    // a `\\.\pipe\` name, and unique per project.
+    let id = project_id.as_uuid().simple().to_string();
+
+    #[cfg(unix)]
+    let addr = unix_runtime_dir()
+        .join(format!("{id}.sock"))
+        .to_string_lossy()
+        .into_owned();
+
+    #[cfg(windows)]
+    let addr = format!(r"\\.\pipe\idea-mcp-{id}");
+
+    #[cfg(not(any(unix, windows)))]
+    let addr = format!("idea-mcp-{id}");
+
+    McpEndpoint { addr }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use uuid::Uuid;
+
+    fn pid(s: &str) -> ProjectId {
+        ProjectId::from_uuid(Uuid::parse_str(s).unwrap())
+    }
+
+    #[test]
+    fn endpoint_is_deterministic_for_the_same_project() {
+        let p = pid("11111111-1111-1111-1111-111111111111");
+        assert_eq!(mcp_endpoint(&p), mcp_endpoint(&p));
+        assert_eq!(mcp_endpoint(&p).as_cli_arg(), mcp_endpoint(&p).as_cli_arg());
+    }
+
+    #[test]
+    fn distinct_projects_get_distinct_endpoints() {
+        let a = pid("11111111-1111-1111-1111-111111111111");
+        let b = pid("22222222-2222-2222-2222-222222222222");
+        assert_ne!(mcp_endpoint(&a), mcp_endpoint(&b));
+        assert_ne!(mcp_endpoint(&a).as_cli_arg(), mcp_endpoint(&b).as_cli_arg());
+    }
+
+    #[test]
+    fn address_encodes_the_project_id_without_hyphens() {
+        let p = pid("abcdef01-2345-6789-abcd-ef0123456789");
+        let arg = mcp_endpoint(&p).as_cli_arg().to_owned();
+        assert!(
+            arg.contains("abcdef0123456789abcdef0123456789"),
+            "endpoint must embed the hyphen-free id, got {arg}"
+        );
+    }
+
+    #[cfg(unix)]
+    #[test]
+    fn unix_endpoint_is_a_sock_path_under_the_runtime_dir() {
+        let p = pid("11111111-1111-1111-1111-111111111111");
+        let ep = mcp_endpoint(&p);
+        let path = ep.socket_path().expect("unix endpoint exposes a socket path");
+        assert!(path.extension().is_some_and(|e| e == "sock"));
+        assert_eq!(path.parent().unwrap(), unix_runtime_dir());
+    }
+}