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/lib.rs

@@ -17,13 +17,49 @@ pub mod chat;
 pub mod commands;
 pub mod dto;
 pub mod events;
+pub mod mcp_bridge;
+pub mod mcp_endpoint;
 pub mod pty;
 pub mod state;
 
+use std::process::ExitCode;
+
 use tauri::Manager;
 
 use state::AppState;
 
+/// The `argv[1]` subcommand token that switches the binary into the headless
+/// `mcp-server` **bridge** mode (cadrage v5 §1.3) instead of launching Tauri.
+pub const MCP_SERVER_SUBCOMMAND: &str = "mcp-server";
+
+/// Process entry point: routes `argv` **before** anything Tauri/WebKit is touched.
+///
+/// When invoked as `<exe> mcp-server …` (an MCP CLI spawned us from the injected
+/// `.mcp.json` declaration), we run the **stdio↔loopback bridge** headless and
+/// **never** initialise the webview — see [`mcp_bridge::run_mcp_bridge`]. Any other
+/// invocation is the normal IDE launch: [`run`] (which blocks until the window
+/// closes and then exits the process itself).
+///
+/// Returns the [`ExitCode`] for the bridge path; the normal path does not return.
+#[must_use]
+pub fn dispatch() -> ExitCode {
+    let mut args = std::env::args_os().skip(1);
+    if args
+        .next()
+        .is_some_and(|a| a == *MCP_SERVER_SUBCOMMAND)
+    {
+        // Headless bridge: bypass Tauri entirely. Forward the remaining args
+        // (`--endpoint`, `--project`, `--requester`) to the bridge parser.
+        let rest: Vec<String> = args
+            .map(|a| a.to_string_lossy().into_owned())
+            .collect();
+        return mcp_bridge::run_mcp_bridge(rest);
+    }
+
+    run();
+    ExitCode::SUCCESS
+}
+
 /// Builds and runs the Tauri application.
 ///
 /// Sets up the composition root (resolving the app-data directory via the Tauri