v0.190.0 — the boot settle window, both gates on intent, and R-171

R-171 (a regression v0.189.0 introduced, CONFIRMED on hardware before any fix
was written). Replacing isBootOrphan's container-count term with recorded intent
made a drive-gate-stopped app read as a boot orphan: the gate stops apps with
`compose down` (zero containers) and never touches desired_state, because it is
not the customer. Observed on 9201 with the drive held unmounted — the sweep
found and started it, burned both attempts, and handed it to the dead-app alarm.
The write hazard did not materialise (the unbound mountpoint is host-root-owned
and the guest is unprivileged) but that protection is accidental and untested.
New consumer-side seam bootrecon.StartGate, fail-safe (cannot determine ⇒ do not
start), wired in main.go. The rule is not new: the API's startGatedByMissingDrive
already refuses this; the sweep bypassed it.

R-157 mechanism A. The sweep looked once at T+5s, deriving candidates from a
fleet docker was still restoring — three of six hard resets. Now a settle-then-
sweep window: sample every 5s, settled after 3 identical samples, sweep ONCE at
the end; ends on settled or a 50s budget, and the log says which. The budget is
50s because settle+budget+one retry must stay under the 90s dead-app grace — a
test rejected 60s at 95s. A window that overruns emits a LATE RECOVERY warn
rather than the grace being widened to hide it.

Widening the window made two more holders reachable, so the one gate covers all
three: an absent drive, a quiesce, and an in-flight app-data operation — reusing
quiesce.SuppressedStacks() and a new read-only AppStopGuard.HeldStacks().

R-170. shouldRecreateOnBoot now reads desired_state with the identical three-way
table; absent keeps the old hasContainers behaviour exactly. Its comment argued
for the container count and was rewritten. presentStable is untouched. The two
gates' agreement is pinned from both sides against one fixture table.

27/27 packages green; 6 red-proofs observed FAIL then restored.

controller/internal/backup/appstop_marker.go

@@ -229,6 +229,24 @@ func (g *AppStopGuard) Recover() *AppStopRecovery {
 	return res
 }
 
+// HeldStacks returns the stacks an app-data operation is CURRENTLY holding down, or nil.
+//
+// Read-only and nil-safe. It exists for the boot reconciler (§8.2): once R-157 mechanism A widened
+// the boot window, the sweep could overlap a running volume dump or export and "recover" an app that
+// is deliberately stopped mid-operation — restarting it under a tar, which is the inconsistency the
+// stop was taken to avoid. Recover() has already run to completion by then, so a marker seen through
+// this method belongs to an operation running NOW, not to a crashed one.
+func (g *AppStopGuard) HeldStacks() []string {
+	if g == nil || g.path == "" {
+		return nil
+	}
+	m, ok := g.read()
+	if !ok || !m.Active {
+		return nil
+	}
+	return append([]string(nil), m.Stacks...)
+}
+
 // ---- marker persistence (atomic, 0600) — the quiesce shape ------------------------------------
 
 func (g *AppStopGuard) write(m AppStopMarker) error {