v0.6.0-rc1: slice 6 Phase A — backup + the self-restore-test (local target)

The guest-level backup layer + the journaled self-restore-test (restore→boot→verify→
teardown) that closes "a backup you haven't restored isn't a backup". All benign
(reuses the slice-4 classifier/gate/journal; no new destructive class/crypto). Local
target only; PBS = Phase B. Restore to a NEW guest only. Backups crash-consistent.

- proxmox: DestroyLXC, VzdumpOptions.Notes (notes-template), LatestBackupVolID.
- reconcile: Engine.RunRestoreTest (journal Scratch entry BEFORE mutation; net link-down
  pre-boot; defer teardown always; benign gated destroy) + Recover extended to reap a
  leaked scratch guest (Scratch flag, special-cased before the UPID path; idempotent).
- internal/backup: runner (vzdump + archive resolve + bulk-gap = backup!=1) + cadence
  scheduler (4th daemon goroutine, default 24h) + in-memory report store.
- hub: Backup/RestoreTest filled; collector seams; cross-repo golden byte-identical +
  bidirectional key-set tests; hub handler logs a FAILED restore-test prominently.
- config BackupConfig (band 990000-990009 default); --selftest=backup / restore-test.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

internal/hub/collect.go

@@ -31,12 +31,25 @@ type StorageObserver interface {
 	Observe(ctx context.Context) ([]StorageTarget, error)
 }
 
+// BackupReporter / RestoreTestReporter are the slice-6 seams the backup layer plugs into
+// (same consumer-side pattern as StorageObserver — hub does not import the backup package).
+// They return the agent's LATEST-known backup-per-target / restore-test result (point-in-time
+// state the backup layer accumulates), not a live scan. A nil reporter → empty slice.
+type BackupReporter interface {
+	Backups(ctx context.Context) []Backup
+}
+type RestoreTestReporter interface {
+	RestoreTests(ctx context.Context) []RestoreTest
+}
+
 // Collector builds a HostReport from read-only sources. All deps are behind narrow
 // interfaces for unit testing.
 type Collector struct {
 	px           proxmoxReader
 	cf           CloudflaredProber
 	storage      StorageObserver
+	backups      BackupReporter
+	restoreTests RestoreTestReporter
 	hostID       string
 	agentVersion string
 	logger       *slog.Logger
@@ -44,8 +57,8 @@ type Collector struct {
 }
 
 // NewCollector builds a collector. hostID echoes config.Hub.HostID; agentVersion is
-// the binary version. storage may be nil (storage_targets emitted empty).
-func NewCollector(px proxmoxReader, cf CloudflaredProber, storage StorageObserver, hostID, agentVersion string, logger *slog.Logger) *Collector {
+// the binary version. storage/backups/restoreTests may be nil (their collections emit empty).
+func NewCollector(px proxmoxReader, cf CloudflaredProber, storage StorageObserver, backups BackupReporter, restoreTests RestoreTestReporter, hostID, agentVersion string, logger *slog.Logger) *Collector {
 	if logger == nil {
 		logger = slog.Default()
 	}
@@ -53,6 +66,8 @@ func NewCollector(px proxmoxReader, cf CloudflaredProber, storage StorageObserve
 		px:           px,
 		cf:           cf,
 		storage:      storage,
+		backups:      backups,
+		restoreTests: restoreTests,
 		hostID:       hostID,
 		agentVersion: agentVersion,
 		logger:       logger,
@@ -79,9 +94,10 @@ func (c *Collector) Collect(ctx context.Context) (*HostReport, error) {
 		// storage_targets populated this slice (slice 5) via the observer; the rest stay
 		// defined-but-empty (slice 6). Non-nil so they marshal as [].
 		StorageTargets: c.collectStorage(ctx),
-		Backups:        []Backup{},
-		RestoreTests:   []RestoreTest{},
-		PBSSnapshots:   []PBSSnapshot{},
+		Backups:        c.collectBackups(ctx),
+		RestoreTests:   c.collectRestoreTests(ctx),
+		PBSSnapshots:   []PBSSnapshot{}, // Phase B
+
 		AuditTail:      []AuditEntry{},
 		Cloudflared:    Cloudflared{Status: c.cloudflaredStatus(ctx)},
 	}
@@ -159,6 +175,29 @@ func (c *Collector) collectStorage(ctx context.Context) []StorageTarget {
 	return targets
 }
 
+// collectBackups / collectRestoreTests read the agent's latest backup + restore-test state
+// via the seams. Best-effort: a nil reporter or nil slice degrades to an empty (non-nil)
+// list so the collection always marshals as [].
+func (c *Collector) collectBackups(ctx context.Context) []Backup {
+	if c.backups == nil {
+		return []Backup{}
+	}
+	if b := c.backups.Backups(ctx); b != nil {
+		return b
+	}
+	return []Backup{}
+}
+
+func (c *Collector) collectRestoreTests(ctx context.Context) []RestoreTest {
+	if c.restoreTests == nil {
+		return []RestoreTest{}
+	}
+	if r := c.restoreTests.RestoreTests(ctx); r != nil {
+		return r
+	}
+	return []RestoreTest{}
+}
+
 func (c *Collector) cloudflaredStatus(ctx context.Context) string {
 	if c.cf == nil {
 		return "unknown"