feat: add deployment foundation and cross-device handoff

internal/state/lock_linux.go

@@ -0,0 +1,26 @@
+//go:build linux
+
+package state
+
+import (
+	"errors"
+	"os"
+	"syscall"
+)
+
+func lockExclusive(f *os.File) error {
+	err := syscall.Flock(int(f.Fd()), syscall.LOCK_EX|syscall.LOCK_NB)
+	if errors.Is(err, syscall.EWOULDBLOCK) || errors.Is(err, syscall.EAGAIN) {
+		return ErrBusy
+	}
+	return err
+}
+
+func syncDirectory(r *os.Root) error {
+	f, err := r.Open(".")
+	if err != nil {
+		return err
+	}
+	defer f.Close()
+	return f.Sync()
+}