controller v0.267.0: tests off DooPlex's Docker, cut-off copies refused, two pages true

R-650: internal/dockerexec — every docker exec routed through it; under
go test a real docker is refused (opt-in FELHOM_TEST_REAL_DOCKER=1; a stub
under the temp dir is allowed). api/stacks/web tests run under a silent
stub (TestMain). TestR650_NoBareDockerExec pins it repo-wide.
R-640: a dump without its engine's completion marker is refused before
the first mutation (unit + off-site restore) and again before any load.
R-499: the Tier-2 page's system-disk sentence has four true branches.
R-518: the backup button states the measured ~8 min stop.
R-626: measured on 9202, not reproduced.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0159rPz1ZhFKsS53msqPYxtS

controller/internal/stacks/samba.go

@@ -2,10 +2,10 @@ package stacks
 
 import (
 	"fmt"
+	"gitea.dooplex.hu/admin/felhom-controller/internal/dockerexec"
 	"gitea.dooplex.hu/admin/felhom-controller/internal/util"
 	"net"
 	"os"
-	"os/exec"
 	"path/filepath"
 	"strings"
 	"time"
@@ -98,7 +98,7 @@ func (m *Manager) SambaImagePresent() bool {
 	if m.sambaImgFn != nil {
 		return m.sambaImgFn()
 	}
-	return exec.Command("docker", "image", "inspect", infra.SambaImage).Run() == nil
+	return dockerexec.Command("docker", "image", "inspect", infra.SambaImage).Run() == nil
 }
 
 // shareAvailable reports whether a share's folder can be exported right now: its owning registered
@@ -287,7 +287,7 @@ func (m *Manager) sambaSetPassword(password string) error {
 	var lastErr error
 	// The container may need a moment to accept exec right after `compose up -d`.
 	for attempt := 1; attempt <= 10; attempt++ {
-		cmd := exec.Command("docker", "exec", "-i", sambaContainer,
+		cmd := dockerexec.Command("docker", "exec", "-i", sambaContainer,
 			"smbpasswd", "-s", "-a", infra.SambaHouseholdUser)
 		cmd.Stdin = strings.NewReader(password + "\n" + password + "\n")
 		out, err := cmd.CombinedOutput()
@@ -350,7 +350,7 @@ func (m *Manager) sambaLANAddr() (string, error) {
 	if m.sambaAddrFn != nil {
 		return m.sambaAddrFn()
 	}
-	out, err := exec.Command("docker", "exec", sambaContainer,
+	out, err := dockerexec.Command("docker", "exec", sambaContainer,
 		"ip", "-4", "-o", "addr", "show", infra.SambaHostInterface).Output()
 	if err != nil {
 		return "", fmt.Errorf("docker exec ip addr: %w", err)