[live-migration] adds the saved state proto for the controllers

Protobuild.toml

@@ -19,8 +19,8 @@ prefixes = [
   "github.com/Microsoft/hcsshim/internal/shimdiag",
   "github.com/Microsoft/hcsshim/internal/extendedtask",
   "github.com/Microsoft/hcsshim/internal/computeagent",
+  "github.com/Microsoft/hcsshim/internal/controller",
   "github.com/Microsoft/hcsshim/internal/ncproxyttrpc",
-  "github.com/Microsoft/hcsshim/internal/vmservice",
   "github.com/Microsoft/hcsshim/pkg/migration",
 ]
 generators = ["go", "go-ttrpc"]

internal/controller/device/plan9/save/constants.go

@@ -0,0 +1,16 @@
+//go:build windows && lcow
+
+// Package save defines the wire format owned by the Plan9 sub-controller
+// for live migration. The [Payload] message is self-contained and carries the
+// Plan9 sub-controller's serialized state (LCOW 9P file shares and their
+// in-guest mounts) across shims.
+package save
+
+// SchemaVersion is the on-the-wire compatibility version stamped into
+// [Payload.SchemaVersion]. Bump on any breaking change to payload.proto.
+const SchemaVersion uint32 = 1
+
+// TypeURL identifies a Plan9 [Payload] when wrapped in an [anypb.Any]. It is
+// opaque to clients and only meaningful between two shims that agree on
+// [SchemaVersion].
+const TypeURL = "type.microsoft.com/hcsshim.controller.plan9.save.v1.Payload"