core: fix canonicality confusion (#19514)

* core: add tests for canonicality confusion

* core: delete stale future canon number mappings during reorg to shorter+heavier chain

core/blockchain.go

@@ -1543,8 +1543,16 @@ func (bc *BlockChain) reorg(oldBlock, newBlock *types.Block) error {
 	for _, tx := range types.TxDifference(deletedTxs, addedTxs) {
 		rawdb.DeleteTxLookupEntry(batch, tx.Hash())
 	}
+	// Delete any canonical number assignments above the new head
+	number := bc.CurrentBlock().NumberU64()
+	for i := number + 1; ; i++ {
+		hash := rawdb.ReadCanonicalHash(bc.db, i)
+		if hash == (common.Hash{}) {
+			break
+		}
+		rawdb.DeleteCanonicalHash(batch, i)
+	}
 	batch.Write()
-
 	// If any logs need to be fired, do it now. In theory we could avoid creating
 	// this goroutine if there are no events to fire, but realistcally that only
 	// ever happens if we're reorging empty blocks, which will only happen on idle