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/appexport/export.go

@@ -6,11 +6,11 @@ import (
 	"compress/gzip"
 	"context"
 	"fmt"
+	"gitea.dooplex.hu/admin/felhom-controller/internal/dockerexec"
 	"gitea.dooplex.hu/admin/felhom-controller/internal/util"
 	"io"
 	"log"
 	"os"
-	"os/exec"
 	"path/filepath"
 	"strings"
 	"sync"
@@ -731,7 +731,7 @@ func (e *Exporter) exportHDDData(req ExportRequest, dataDir string, manifest *Ma
 // controller itself runs containerized (the v0.124.0 HIGH finding). Package var so unit tests
 // inject a recorder (no docker on test boxes).
 var dockerExec = func(ctx context.Context, stdin io.Reader, stdout io.Writer, args ...string) (string, error) {
-	cmd := exec.CommandContext(ctx, "docker", args...)
+	cmd := dockerexec.CommandContext(ctx, "docker", args...)
 	cmd.Stdin = stdin
 	cmd.Stdout = stdout
 	var errBuf bytes.Buffer