Fix A: the stable-start sampler says at DEBUG why a sample is not ok (a live run on 9202 judged a healthy app unstable; the reason was not logged). Commit only.

controller/internal/backup/restore_verdict.go

@@ -144,6 +144,7 @@ const (
 // stableSample is one look: ok, and the fingerprint (container id → restart count) a stable window must keep.
 func (m *Manager) stableSample(stack string) (bool, map[string]int) {
 	if m.stackProvider == nil || !m.stackProvider.RefreshAndIsRunning(stack) {
+		m.debugStable(stack, "the stack does not read running")
 		return false, nil
 	}
 	cs, ok := m.stackProvider.(containerSampler)
@@ -152,11 +153,13 @@ func (m *Manager) stableSample(stack string) (bool, map[string]int) {
 	}
 	samples, err := cs.ContainerSamples(stack)
 	if err != nil || len(samples) == 0 {
+		m.debugStable(stack, fmt.Sprintf("no container sample (%d, err %v)", len(samples), err))
 		return false, nil
 	}
 	fp := make(map[string]int, len(samples))
 	for _, c := range samples {
 		if !c.Running || (c.Health != "" && c.Health != "healthy") {
+			m.debugStable(stack, fmt.Sprintf("container %.12s running=%v health=%q", c.ID, c.Running, c.Health))
 			return false, nil
 		}
 		fp[c.ID] = c.RestartCount
@@ -164,6 +167,12 @@ func (m *Manager) stableSample(stack string) (bool, map[string]int) {
 	return true, fp
 }
 
+func (m *Manager) debugStable(stack, why string) {
+	if m.logger != nil && m.isDebug() {
+		m.logger.Printf("[DEBUG] [backup] stable-start sample %s: not ok — %s", stack, why)
+	}
+}
+
 func sameRestartFingerprint(a, b map[string]int) bool {
 	if len(a) != len(b) {
 		return false