fix(block): fix replay logic (#3053)

* claude replay fix

* reduce comments

* prep rc.3

Author: julienrbrt

CHANGELOG.md

@@ -9,6 +9,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+## v1.0.0-rc.3
+
 ### Added
 
 - Add DA Hints for P2P transactions. This allows a catching up node to be on sync with both DA and P2P. ([#2891](https://github.com/evstack/ev-node/pull/2891))
@@ -18,6 +20,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Improve `cache.NumPendingData` to not return empty data. Automatically bumps `LastSubmittedHeight` to reflect that. ([#3046](https://github.com/evstack/ev-node/pull/3046))
 - **BREAKING** Make pending events cache and tx cache fully ephemeral. Those will be re-fetched on restart. DA Inclusion cache persists until cleared up after DA inclusion has been processed. Persist accross restart using store metadata. ([#3047](https://github.com/evstack/ev-node/pull/3047))
 - Replace LRU cache by standard mem cache with manual eviction in `store_adapter`. When P2P blocks were fetched too fast, they would be evicted before being executed [#3051](https://github.com/evstack/ev-node/pull/3051)
+- Fix replay logic leading to app hashes by verifying against the wrong block [#3053](https://github.com/evstack/ev-node/pull/3053).
 
 ## v1.0.0-rc.2
 

block/internal/common/replay.go

@@ -150,27 +150,21 @@ func (s *Replayer) replayBlock(ctx context.Context, height uint64) error {
 	// Get the previous state
 	var prevState types.State
 	if height == s.genesis.InitialHeight {
-		// For the first block, use genesis state
+		// For the first block, use genesis state.
 		prevState = types.State{
 			ChainID:         s.genesis.ChainID,
 			InitialHeight:   s.genesis.InitialHeight,
 			LastBlockHeight: s.genesis.InitialHeight - 1,
 			LastBlockTime:   s.genesis.StartTime,
-			AppHash:         header.AppHash, // This will be updated by InitChain
+			AppHash:         header.AppHash, // Genesis app hash (input to first block execution)
 		}
 	} else {
-		// Get previous state from store
+		// GetStateAtHeight(height-1) returns the state AFTER block height-1 was executed,
+		// which contains the correct AppHash to use as input for executing block at 'height'.
 		prevState, err = s.store.GetStateAtHeight(ctx, height-1)
 		if err != nil {
 			return fmt.Errorf("failed to get previous state: %w", err)
 		}
-		// We need the state at height-1, so load that block's app hash
-		prevHeader, _, err := s.store.GetBlockData(ctx, height-1)
-		if err != nil {
-			return fmt.Errorf("failed to get previous block header: %w", err)
-		}
-		prevState.AppHash = prevHeader.AppHash
-		prevState.LastBlockHeight = height - 1
 	}
 
 	// Prepare transactions
@@ -190,27 +184,39 @@ func (s *Replayer) replayBlock(ctx context.Context, height uint64) error {
 		return fmt.Errorf("failed to execute transactions: %w", err)
 	}
 
-	// DEBUG: Log comparison of expected vs actual app hash
-	s.logger.Debug().
-		Uint64("height", height).
-		Str("expected_app_hash", hex.EncodeToString(header.AppHash)).
-		Str("actual_app_hash", hex.EncodeToString(newAppHash)).
-		Bool("hashes_match", bytes.Equal(newAppHash, header.AppHash)).
-		Msg("replayBlock: ExecuteTxs completed")
-
-	// Verify the app hash matches
-	if !bytes.Equal(newAppHash, header.AppHash) {
-		err := fmt.Errorf("app hash mismatch: expected %s got %s",
-			hex.EncodeToString(header.AppHash),
-			hex.EncodeToString(newAppHash),
-		)
-		s.logger.Error().
-			Str("expected", hex.EncodeToString(header.AppHash)).
-			Str("got", hex.EncodeToString(newAppHash)).
+	// The result of ExecuteTxs (newAppHash) should match the stored state at this height.
+	// Note: header.AppHash is the PREVIOUS state's app hash (input), not the expected output.
+	// The expected output is stored in state[height].AppHash or equivalently in header[height+1].AppHash.
+
+	// For verification, we need to get the expected app hash from the stored state at this height.
+	// If this state doesn't exist (which would be unusual since we fetched the block), we skip verification.
+	expectedState, err := s.store.GetStateAtHeight(ctx, height)
+	if err == nil {
+		// State exists, verify the app hash matches
+		if !bytes.Equal(newAppHash, expectedState.AppHash) {
+			err := fmt.Errorf("app hash mismatch at height %d: expected %s got %s",
+				height,
+				hex.EncodeToString(expectedState.AppHash),
+				hex.EncodeToString(newAppHash),
+			)
+			s.logger.Error().
+				Str("expected", hex.EncodeToString(expectedState.AppHash)).
+				Str("got", hex.EncodeToString(newAppHash)).
+				Uint64("height", height).
+				Err(err).
+				Msg("app hash mismatch during replay")
+			return err
+		}
+		s.logger.Debug().
+			Uint64("height", height).
+			Str("app_hash", hex.EncodeToString(newAppHash)).
+			Msg("replayBlock: app hash verified against stored state")
+	} else {
+		// State doesn't exist yet, we trust the execution result since we're replaying validated blocks.
+		s.logger.Debug().
 			Uint64("height", height).
-			Err(err).
-			Msg("app hash mismatch during replay")
-		return err
+			Str("app_hash", hex.EncodeToString(newAppHash)).
+			Msg("replayBlock: ExecuteTxs completed (no stored state to verify against)")
 	}
 
 	// Calculate new state