cmd/era: fix iterator error source handling in checkAccumulator (ethereum#32698)

This change replaces wrapping a stale outer err with the iterator’s own error after Next(), and switches the post-BlockAndReceipts() check to use the returned err. According to internal/era iterator contract, Error() should be consulted immediately after Next() to surface iteration errors, while decoding errors from Block/Receipts are returned directly. The previous code could hide the real failure (using nil or unrelated err), leading to misleading diagnostics and missed iteration errors. --------- Co-authored-by: lightclient <lightclient@protonmail.com>

Author: MozirDmitriy

cmd/era/main.go

@@ -274,10 +274,10 @@ func checkAccumulator(e *era.Era) error {
 for it.Next() {
 // 1) next() walks the block index, so we're able to implicitly verify it.
 if it.Error() != nil {
-return fmt.Errorf("error reading block %d: %w", it.Number(), err)
+return fmt.Errorf("error reading block %d: %w", it.Number(), it.Error())
 }
 block, receipts, err := it.BlockAndReceipts()
-if it.Error() != nil {
+if err != nil {
 return fmt.Errorf("error reading block %d: %w", it.Number(), err)
 }
 // 2) recompute tx root and verify against header.
@@ -294,6 +294,9 @@ func checkAccumulator(e *era.Era) error {
 td.Add(td, block.Difficulty())
 tds = append(tds, new(big.Int).Set(td))
 }
+if it.Error() != nil {
+return fmt.Errorf("error reading block %d: %w", it.Number(), it.Error())
+}
 // 4+5) Verify accumulator and total difficulty.
 got, err := era.ComputeAccumulator(hashes, tds)
 if err != nil {