tailscale: Add tailssh server

protocol/tailscale/tailssh/session.go

@@ -0,0 +1,33 @@
+//go:build with_gvisor
+
+package tailssh
+
+import (
+	"io"
+
+	"github.com/sagernet/sing-box/adapter"
+)
+
+type shellBackend interface {
+	OpenSession(request shellRequest) (shellSession, error)
+	Close() error
+}
+
+type shellRequest struct {
+	User    *adapter.PlatformUser
+	Command string
+	Env     []string
+	Term    string
+	Rows    uint16
+	Cols    uint16
+}
+
+type shellSession interface {
+	io.ReadWriteCloser
+	// CloseWrite signals EOF on the child's stdin without tearing down the
+	// session, so programs that read stdin to EOF can finish normally.
+	CloseWrite() error
+	Resize(rows, cols uint16) error
+	Signal(sig int) error
+	Wait() (exitStatus uint32, err error)
+}