feat(privilege): acquire sudo and keep timestamp fresh via goroutine

internal/privilege/sudo.go

@@ -0,0 +1,77 @@
+// Package privilege manages sudo timestamp acquisition and keepalive so
+// a long-running installer only prompts once.
+package privilege
+
+import (
+	"context"
+	"fmt"
+	"os/exec"
+	"time"
+)
+
+// Keepalive holds the lifetime of a background sudo-refresh goroutine.
+type Keepalive struct {
+	cancel context.CancelFunc
+	done   chan struct{}
+}
+
+// Stop terminates the keepalive goroutine. Safe to call multiple times.
+func (k *Keepalive) Stop() {
+	if k == nil || k.cancel == nil {
+		return
+	}
+	k.cancel()
+	<-k.done
+	k.cancel = nil
+}
+
+// Acquirer abstracts the `sudo` binary so tests can inject a fake.
+type Acquirer interface {
+	Validate(ctx context.Context) error               // sudo -v (may prompt)
+	ValidateNonInteractive(ctx context.Context) error // sudo -n -v
+}
+
+// ExecSudo is the production Acquirer.
+type ExecSudo struct{}
+
+func (ExecSudo) Validate(ctx context.Context) error {
+	cmd := exec.CommandContext(ctx, "sudo", "-v")
+	cmd.Stdin = nil // inherit terminal stdin
+	return cmd.Run()
+}
+
+func (ExecSudo) ValidateNonInteractive(ctx context.Context) error {
+	return exec.CommandContext(ctx, "sudo", "-n", "-v").Run()
+}
+
+// Acquire runs `sudo -v` once (prompting if needed) and returns a Keepalive
+// that refreshes the timestamp every `interval` using ValidateNonInteractive.
+// If the initial Validate fails, no goroutine is started and the error is returned.
+func Acquire(ctx context.Context, a Acquirer, interval time.Duration) (*Keepalive, error) {
+	if a == nil {
+		a = ExecSudo{}
+	}
+	if interval <= 0 {
+		interval = 50 * time.Second
+	}
+	if err := a.Validate(ctx); err != nil {
+		return nil, fmt.Errorf("sudo -v failed: %w", err)
+	}
+	kCtx, cancel := context.WithCancel(ctx)
+	k := &Keepalive{cancel: cancel, done: make(chan struct{})}
+
+	go func() {
+		defer close(k.done)
+		t := time.NewTicker(interval)
+		defer t.Stop()
+		for {
+			select {
+			case <-kCtx.Done():
+				return
+			case <-t.C:
+				_ = a.ValidateNonInteractive(kCtx) // best-effort
+			}
+		}
+	}()
+	return k, nil
+}