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/web/handlers.go

@@ -5,11 +5,11 @@ import (
 	"context"
 	"errors"
 	"fmt"
+	"gitea.dooplex.hu/admin/felhom-controller/internal/dockerexec"
 	"log"
 	"net/http"
 	"net/url"
 	"os"
-	"os/exec"
 	"path/filepath"
 	"sort"
 	"strings"
@@ -3383,7 +3383,7 @@ func (s *Server) syncFileBrowserMounts(resetDBOnChange bool) {
 		s.logger.Printf("[INFO] [web] FileBrowser sources changed — resetting database (restore mode)")
 		resetCtx, resetCancel := context.WithTimeout(context.Background(), 30*time.Second)
 		defer resetCancel()
-		stop := exec.CommandContext(resetCtx, "docker", "compose", "down", "-v")
+		stop := dockerexec.CommandContext(resetCtx, "docker", "compose", "down", "-v")
 		stop.Dir = stackDir
 		if out, err := stop.CombinedOutput(); err != nil {
 			s.logger.Printf("[WARN] [web] FileBrowser down -v: %s — %v", strings.TrimSpace(string(out)), err)
@@ -3399,7 +3399,7 @@ func (s *Server) syncFileBrowserMounts(resetDBOnChange bool) {
 	if changed {
 		args = []string{"compose", "up", "-d", "--force-recreate", "--remove-orphans"}
 	}
-	cmd := exec.CommandContext(ctx, "docker", args...)
+	cmd := dockerexec.CommandContext(ctx, "docker", args...)
 	cmd.Dir = stackDir
 	if out, err := cmd.CombinedOutput(); err != nil {
 		s.logger.Printf("[ERROR] [web] Failed to bring up FileBrowser: %s — %v", string(out), err)