db/state: fix data race between buildFiles and recalcVisibleFiles

buildFiles() calls BeginFilesRo() on Domain and InvertedIndex without
holding visibleFilesLock, racing with recalcVisibleFiles() which writes
_visible/_visibleFiles under the same lock. Wrap the BeginFilesRo()
calls in buildFiles() with visibleFilesLock.RLock() to synchronize
with the writer, matching the pattern already used in
Aggregator.BeginFilesRo().

Fixes TestHistoryVerification_WithUserTransactions DATA RACE.

Co-Authored-By: Claude Opus 4.6 <[email protected]>

Author: Giulio2002

db/state/aggregator.go

@@ -687,6 +687,10 @@ func (a *Aggregator) buildFiles(ctx context.Context, step kv.Step) error {
 
 	g, ctx := errgroup.WithContext(ctx)
 	g.SetLimit(a.collateAndBuildWorkers)
+
+	// Acquire read lock to protect BeginFilesRo() calls from concurrent writes
+	// by recalcVisibleFiles() in BuildMissedAccessorsInBackground.
+	a.visibleFilesLock.RLock()
 	for _, d := range a.d {
 		if d.Disable {
 			continue
@@ -768,6 +772,7 @@ func (a *Aggregator) buildFiles(ctx context.Context, step kv.Step) error {
 			return nil
 		})
 	}
+	a.visibleFilesLock.RUnlock()
 	if err := g.Wait(); err != nil {
 		static.CleanupOnError()
 		return fmt.Errorf("domain collate-build: %w", err)