fix(cleanup): resolve CHECK constraint failure and add tombstone pruning

- Fix bd-tnsq: executeDelete now sets closed_at=NULL when creating
  tombstones, satisfying the CHECK constraint that requires
  closed_at IS NULL when status != 'closed'

- Fix bd-08ea: cleanup command now also prunes expired tombstones
  (older than 30 days) after converting closed issues to tombstones

- Add regression test for batch deletion of closed issues

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

cmd/bd/compact.go

@@ -1076,6 +1076,58 @@ func pruneExpiredTombstones() (*TombstonePruneResult, error) {
 	}, nil
 }
 
+// previewPruneTombstones checks what tombstones would be pruned without modifying files.
+// Used for dry-run mode in cleanup command (bd-08ea).
+func previewPruneTombstones() (*TombstonePruneResult, error) {
+	beadsDir := filepath.Dir(dbPath)
+	issuesPath := filepath.Join(beadsDir, "issues.jsonl")
+
+	// Check if issues.jsonl exists
+	if _, err := os.Stat(issuesPath); os.IsNotExist(err) {
+		return &TombstonePruneResult{}, nil
+	}
+
+	// Read all issues
+	// nolint:gosec // G304: issuesPath is controlled from beadsDir
+	file, err := os.Open(issuesPath)
+	if err != nil {
+		return nil, fmt.Errorf("failed to open issues.jsonl: %w", err)
+	}
+	defer file.Close()
+
+	var allIssues []*types.Issue
+	decoder := json.NewDecoder(file)
+	for {
+		var issue types.Issue
+		if err := decoder.Decode(&issue); err != nil {
+			if err.Error() == "EOF" {
+				break
+			}
+			// Skip corrupt lines
+			continue
+		}
+		allIssues = append(allIssues, &issue)
+	}
+
+	// Determine TTL
+	ttl := types.DefaultTombstoneTTL
+	ttlDays := int(ttl.Hours() / 24)
+
+	// Count expired tombstones
+	var prunedIDs []string
+	for _, issue := range allIssues {
+		if issue.IsExpired(ttl) {
+			prunedIDs = append(prunedIDs, issue.ID)
+		}
+	}
+
+	return &TombstonePruneResult{
+		PrunedCount: len(prunedIDs),
+		PrunedIDs:   prunedIDs,
+		TTLDays:     ttlDays,
+	}, nil
+}
+
 func init() {
 	compactCmd.Flags().BoolVar(&compactDryRun, "dry-run", false, "Preview without compacting")
 	compactCmd.Flags().IntVar(&compactTier, "tier", 1, "Compaction tier (1 or 2)")