go/consensus/tendermint: Use our notion of latest height

Do not let Tendermint determine the latest height as that completely ignores
ABCI processing so it can return a block for which local state does not yet
exist.

.changelog/2786.bugfix.md

@@ -0,0 +1,5 @@
+go/consensus/tendermint: Use our notion of latest height
+
+Do not let Tendermint determine the latest height as that completely ignores
+ABCI processing so it can return a block for which local state does not yet
+exist.

go/consensus/tendermint/abci/mux.go

@@ -265,6 +265,11 @@ func (a *ApplicationServer) EstimateGas(caller signature.PublicKey, tx *transact
 	return a.mux.EstimateGas(caller, tx)
 }
 
+// BlockHeight returns the last committed block height.
+func (a *ApplicationServer) BlockHeight() int64 {
+	return a.mux.state.BlockHeight()
+}
+
 // NewApplicationServer returns a new ApplicationServer, using the provided
 // directory to persist state.
 func NewApplicationServer(ctx context.Context, upgrader upgrade.Backend, cfg *ApplicationConfig) (*ApplicationServer, error) {

go/consensus/tendermint/tendermint.go

@@ -807,13 +807,16 @@ func (t *tendermintService) GetTendermintBlock(ctx context.Context, height int64
 		return nil, ctx.Err()
 	}
 
-	var tmHeight *int64
+	var tmHeight int64
 	if height == consensusAPI.HeightLatest {
-		tmHeight = nil
+		// Do not let Tendermint determine the latest height (e.g., by passing nil here) as that
+		// completely ignores ABCI processing so it can return a block for which local state does
+		// not yet exist. Use our mux notion of latest height instead.
+		tmHeight = t.mux.BlockHeight()
 	} else {
-		tmHeight = &height
+		tmHeight = height
 	}
-	result, err := t.client.Block(tmHeight)
+	result, err := t.client.Block(&tmHeight)
 	if err != nil {
 		return nil, fmt.Errorf("tendermint: block query failed: %w", err)
 	}