fix catchup height check

Author: julienrbrt

block/internal/syncing/syncer.go

@@ -786,33 +786,33 @@ func (s *Syncer) TrySyncNextBlock(ctx context.Context, event *common.DAHeightEve
 	// instead of the next forced-inclusion epoch), causing valid catch-up blocks
 	// to be incorrectly flagged as malicious.
 	//
-	// To handle this, when the gap exceeds one DA epoch, we advance DAHeight by
-	// exactly one epoch per block. This lets the forced inclusion verifier check
-	// the correct epoch for each catch-up block. Once the sequencer finishes
-	// catching up and the gap closes, DAHeight converges to event.DaHeight.
+	// To handle this, when the gap exceeds one DA epoch, we compute the epoch
+	// start that contains event.DaHeight and set DAHeight to that epoch start.
+	// This ensures all blocks from the same DA epoch verify against the same
+	// epoch. Once the sequencer finishes catching up and the gap closes,
+	// DAHeight converges to event.DaHeight.
 	if event.DaHeight > newState.DAHeight {
 		epochSize := s.genesis.DAEpochForcedInclusion
 		gap := event.DaHeight - newState.DAHeight
 
 		if epochSize > 0 && gap > epochSize {
 			// Large gap detected — likely catch-up blocks from a restarted sequencer.
-			// Advance DAHeight by one epoch to keep forced inclusion verification
-			// aligned with the epoch the sequencer is replaying.
-			_, epochEnd, _ := types.CalculateEpochBoundaries(
-				newState.DAHeight, s.genesis.DAStartHeight, epochSize,
+			// Compute the epoch start that contains event.DaHeight so all blocks
+			// from the same epoch verify against the same DA epoch.
+			epochStart, _, _ := types.CalculateEpochBoundaries(
+				event.DaHeight, s.genesis.DAStartHeight, epochSize,
 			)
-			nextEpochStart := epochEnd + 1
-			if nextEpochStart > event.DaHeight {
+			if epochStart > event.DaHeight {
 				// Shouldn't happen, but clamp to event.DaHeight as a safety net.
-				nextEpochStart = event.DaHeight
+				epochStart = event.DaHeight
 			}
 			s.logger.Debug().
 				Uint64("current_da_height", newState.DAHeight).
 				Uint64("event_da_height", event.DaHeight).
-				Uint64("advancing_to", nextEpochStart).
+				Uint64("epoch_start", epochStart).
 				Uint64("gap", gap).
-				Msg("large DA height gap detected (sequencer catch-up), advancing DA height by one epoch")
-			newState.DAHeight = nextEpochStart
+				Msg("large DA height gap detected (sequencer catch-up), setting DA height to epoch start")
+			newState.DAHeight = epochStart
 		} else {
 			newState.DAHeight = event.DaHeight
 		}