v0.237.0: the Update button takes a backup first, and tells the truth (update arc slice 4 — R-448, R-443, R-439)

POST /api/stacks/{name}/update is now a guarded job answering 202:
cheap refusals (hold — R-439, busy, migration, deploying, memory via the
deploy's own memoryVerdict, a fixed 2 GB disk floor, and no restorable
Tier-2 copy) → backup-first when the proven copy is older than
update.backup_max_age (24h) → safety dump BEFORE the pin moves → pin →
pull (failure puts the pin back) → up → health (.felhom.yml check or 60 s
settle, update.health_timeout 5m). Not healthy → the app is stopped and
HELD (RestoreHold reason update_failed, same store and gate as R-379) and
the page names the backup to restore from; the pin stays. Success is only
ever update_phase=done after health (R-443). UpdateStack is deleted.

The restorable-unit predicate is EXTRACTED to backup.Tier2UnitRestorePoint
and shared with the backups page (row pinned unchanged). The copy is aged
by the last successful Tier-2 copy, not the manifest created_at — measured
on demo-hp that created_at moves only on definition changes.

Crash safety: update-journal.json before each phase; RecoverUpdates before
the boot sweep, ResumeInterruptedUpdates after the guards are wired.

Three unattended start paths ignored a hold and now honour it: the
drive-return gate (restart + boot recreate) and the nightly volume dump.
The nightly capture and Tier-2 run skip held apps so the restore point
survives. No automatic rollback — measured per-app; route back = restore.

Tests A–H across stacks/backup/api/web/cmd; six red-proofs seen to fail.

Claude-Session: https://claude.ai/code/session_0159rPz1ZhFKsS53msqPYxtS

controller/internal/web/slice4_update_test.go

@@ -0,0 +1,74 @@
+package web
+
+import (
+	"os"
+	"path/filepath"
+	"testing"
+	"time"
+
+	"gitea.dooplex.hu/admin/felhom-controller/internal/backup"
+	"gitea.dooplex.hu/admin/felhom-controller/internal/settings"
+)
+
+// Slice 4 — the predicate moved from this package into backup.Tier2UnitRestorePoint. The page must
+// render IDENTICALLY: the row's four unit-restore fields are compared against the coverage computed
+// the old way (the inline expression that used to live in buildAppBackupRows).
+func TestSlice4_BackupRowUnitFieldsAreUnchangedByTheExtraction(t *testing.T) {
+	s, sett, m := newOffboxWebServer(t)
+	dest := t.TempDir()
+	if err := sett.AddStoragePath(settings.StoragePath{Path: dest, Label: "flash"}); err != nil {
+		t.Fatal(err)
+	}
+	if err := sett.SetCrossDriveConfig("app", &settings.CrossDriveBackup{
+		Enabled: true, Method: "rsync", DestinationPath: dest,
+		LastRun: "2026-09-13T01:30:00Z", LastStatus: "ok", LastSuccess: "2026-09-13T01:30:00Z", SuccessTracked: true,
+	}); err != nil {
+		t.Fatal(err)
+	}
+	unit := filepath.Join(dest, "backups", "secondary", "app", "recovery-unit")
+	if err := os.MkdirAll(unit, 0o755); err != nil {
+		t.Fatal(err)
+	}
+	if err := os.WriteFile(filepath.Join(unit, "manifest.json"), []byte(`{"schema_version":2,"app_name":"app","created_at":"2026-09-12T02:15:29Z"}`), 0o644); err != nil {
+		t.Fatal(err)
+	}
+	if err := os.WriteFile(filepath.Join(dest, "backups", "secondary", "app", ".felhom-tier2-layout"), []byte("2"), 0o644); err != nil {
+		t.Fatal(err)
+	}
+
+	cov, err := m.Tier2RestoreCoverage("app")
+	if err != nil {
+		t.Fatal(err)
+	}
+	wantDate, wantStale := cov.UnitRestoreDate()
+	rows := s.buildAppBackupRows(&backup.FullBackupStatus{AppDataInfo: []backup.AppBackupInfo{{StackName: "app", DisplayName: "App"}}})
+	row := findRow(rows, "app")
+	if row == nil {
+		t.Fatal("no row")
+	}
+	if !cov.CanRestoreUnit() {
+		t.Fatal("fixture: the copy must hold an openable unit")
+	}
+	if row.Tier2UnitRestorable != cov.CanRestoreUnit() || row.Tier2CopyDate != wantDate ||
+		row.Tier2CopyDateProven != (cov.CopyLastSuccess != "") ||
+		row.Tier2UnitConfirm != tier2UnitConfirmWithStaleness(wantDate, cov.CopyLastSuccess != "", wantStale) {
+		t.Errorf("the row changed: restorable=%v date=%q proven=%v confirm=%q", row.Tier2UnitRestorable, row.Tier2CopyDate, row.Tier2CopyDateProven, row.Tier2UnitConfirm)
+	}
+}
+
+// The drive-return gate starts apps UNATTENDED. A held app must be skipped.
+//
+// COMPANION RED-PROOF (REPORT.md): delete the appHeld check from restartStacks. The server has NO stack
+// manager here on purpose, so the unguarded StartStack call panics and this test fails.
+func TestSlice4_DriveReturnGateSkipsAHeldApp(t *testing.T) {
+	s, _, m := newOffboxWebServer(t)
+	if err := m.HoldAfterFailedUpdate("held", time.Now(), time.Now()); err != nil {
+		t.Fatal(err)
+	}
+	defer func() {
+		if r := recover(); r != nil {
+			t.Fatalf("the drive-return gate tried to START a held app: %v", r)
+		}
+	}()
+	s.restartStacks([]string{"held"})
+}