fix: SSH control socket path in WSL2 when runtime dir doesn't exist (fixes #319)

pkg/client/connector/sshcli.go

@@ -45,9 +45,13 @@ func controlSocketPath() string {
 	// of the ProxyJump option. This ensures that shared connections are uniquely identified.
 	sockName := fmt.Sprintf("uc_control_%%C.sock")
 
-	// Prefer XDG_RUNTIME_DIR if set, fall back to ~/.ssh if it exists.
+	// Prefer XDG_RUNTIME_DIR if set and the directory exists, fall back to ~/.ssh if it exists.
 	if dir := os.Getenv("XDG_RUNTIME_DIR"); dir != "" {
-		return filepath.Join(dir, sockName)
+		// On WSL2 without systemd, XDG_RUNTIME_DIR may be set to /run/user/$UID that doesn't actually exist,
+		// so existence must be verified before use: https://github.com/psviderski/uncloud/issues/319.
+		if fi, err := os.Stat(dir); err == nil && fi.IsDir() {
+			return filepath.Join(dir, sockName)
+		}
 	}
 	if home, err := os.UserHomeDir(); err == nil {
 		sshDir := filepath.Join(home, ".ssh")

pkg/client/connector/sshcli_test.go

@@ -109,11 +109,20 @@ func TestControlSocketPath(t *testing.T) {
 	assert.True(t, strings.HasSuffix(path1, ".sock"))
 	assert.Contains(t, path1, "%C")
 
-	t.Run("uses XDG_RUNTIME_DIR when set", func(t *testing.T) {
-		runDir := "/user/runtime/dir"
+	t.Run("uses XDG_RUNTIME_DIR when set and exists", func(t *testing.T) {
+		runDir := t.TempDir()
 		t.Setenv("XDG_RUNTIME_DIR", runDir)
 
 		path := controlSocketPath()
 		assert.True(t, strings.HasPrefix(path, runDir))
 	})
+
+	t.Run("falls back when XDG_RUNTIME_DIR is set but missing", func(t *testing.T) {
+		// WSL2 without systemd sets XDG_RUNTIME_DIR to a path that doesn't exist.
+		t.Setenv("XDG_RUNTIME_DIR", "/nonexistent/uncloud-test-xdg")
+
+		path := controlSocketPath()
+		assert.NotEmpty(t, path)
+		assert.False(t, strings.HasPrefix(path, "/nonexistent/"))
+	})
 }