diff --git a/crates/app-tauri/src/mcp_endpoint.rs b/crates/app-tauri/src/mcp_endpoint.rs
index b4dc728..3f9204b 100644
--- a/crates/app-tauri/src/mcp_endpoint.rs
+++ b/crates/app-tauri/src/mcp_endpoint.rs
@@ -87,13 +87,29 @@ impl McpEndpoint {
 /// 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).
+///
+/// The candidate bases are tried **in priority order**, returning the first whose
+/// `idea-mcp` subdir exists or can be created. A set-but-unusable `$XDG_RUNTIME_DIR`
+/// (e.g. a sandbox/CI where it points at a non-existent or read-only path) must not
+/// dead-end the loopback bind: without this fallback the socket silently never
+/// binds and inter-agent delegation dies. Deterministic for a given environment, so
+/// the bind side and any `socket_path()` reader always agree on the same directory.
 #[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")
+    let candidates = [
+        std::env::var_os("XDG_RUNTIME_DIR").map(PathBuf::from),
+        std::env::var_os("TMPDIR").map(PathBuf::from),
+        Some(PathBuf::from("/tmp")),
+    ];
+    for base in candidates.into_iter().flatten() {
+        let dir = base.join("idea-mcp");
+        if dir.is_dir() || std::fs::create_dir_all(&dir).is_ok() {
+            return dir;
+        }
+    }
+    // Last resort: keep the historical `/tmp` target even if creation just failed
+    // (the bind will surface the real error rather than silently picking nowhere).
+    PathBuf::from("/tmp").join("idea-mcp")
 }
 
 /// **Single source of truth.** Computes the deterministic loopback endpoint of a