R-366 slice 2 (decision 168): the host report carries the archives the restore-test skipped as another key's

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0159rPz1ZhFKsS53msqPYxtS

internal/backup/runner.go

@@ -66,8 +66,13 @@ type BackupRunner struct {
 	// due-check is served from the local-API handler goroutines.
 	rejectedMu sync.Mutex
 	rejected   map[string]struct{}
+	// foreign (R-366 slice 2) records, per tier, the archives the pick skipped as another key's. nil = not wired.
+	foreign *ForeignKeyLedger
 }
 
+// SetForeignKeyLedger wires the R-366 slice-2 ledger the host report reads.
+func (r *BackupRunner) SetForeignKeyLedger(l *ForeignKeyLedger) { r.foreign = l }
+
 // NewBackupRunner builds a runner. mode defaults to snapshot (works for a stopped guest and
 // for lvm-thin); the caller may pass ModeStop for storages without snapshot support. retention is the
 // per-run prune spec ("keep-last=N", or "" to never prune) — only the periodic local backup sets it.
@@ -370,6 +375,8 @@ func (r *BackupRunner) PickSettledRestoreCandidateOn(ctx context.Context, target
 	var best string
 	var bestCTime int64 = -1
 	known := map[int]bool{} // vmid → the guest exists on this node (asked once per vmid per pick)
+	var foreignN int        // R-366 slice 2: archives skipped as another key's, and their time range
+	var foreignMin, foreignMax int64
 	for _, e := range contents {
 		if e.Content != "backup" {
 			continue
@@ -384,6 +391,13 @@ func (r *BackupRunner) PickSettledRestoreCandidateOn(ctx context.Context, target
 		}
 		if ownKey != "" && !strings.EqualFold(e.Encrypted, ownKey) {
 			r.noteNotAGuestBackupOnce(e, fmt.Sprintf("written by another box (key %s, this box's key %s) — not this box's proof", shortFP(e.Encrypted), shortFP(ownKey)))
+			foreignN++
+			if foreignMin == 0 || e.CTime < foreignMin {
+				foreignMin = e.CTime
+			}
+			if e.CTime > foreignMax {
+				foreignMax = e.CTime
+			}
 			continue
 		}
 		// R-689 (v0.136.0): … OF A GUEST THAT STILL EXISTS here. Measured on demo-hp 2026-09-27 right after
@@ -420,6 +434,9 @@ func (r *BackupRunner) PickSettledRestoreCandidateOn(ctx context.Context, target
 			bestCTime, best = e.CTime, e.VolID
 		}
 	}
+	if r.foreign != nil {
+		r.foreign.set(target, foreignN, foreignMin, foreignMax)
+	}
 	if best == "" {
 		return "", time.Time{}, nil
 	}