fix(consensus): enforce tx versions across fork eras

Co-Authored-By: Charon <charon@lethean.io>

consensus/tx.go

@@ -75,26 +75,32 @@ func ValidateTransaction(tx *types.Transaction, txBlob []byte, forks []config.Ha
 // checkTxVersion validates that the transaction version is appropriate for the
 // current hardfork era.
 //
-// After HF5: transaction version must be exactly VersionPostHF5 (3) and the
-// embedded hardfork_id must match the active hardfork version.
-// Before HF5: transaction version 3 is rejected (too early).
+// Pre-HF4: regular transactions must use version 1.
+// HF4 era: regular transactions must use version 2.
+// HF5+: transaction version must be exactly version 3 and the embedded
+// hardfork_id must match the active hardfork version.
 func checkTxVersion(tx *types.Transaction, forks []config.HardFork, height uint64) error {
 	hf5Active := config.IsHardForkActive(forks, config.HF5, height)
+	hf4Active := config.IsHardForkActive(forks, config.HF4Zarcanum, height)
 	currentFork := config.VersionAtHeight(forks, height)
 
-	if hf5Active && tx.Version != types.VersionPostHF5 {
+	var expectedVersion uint64
+	switch {
+	case hf5Active:
+		expectedVersion = types.VersionPostHF5
+	case hf4Active:
+		expectedVersion = types.VersionPostHF4
+	default:
+		expectedVersion = types.VersionPreHF4
+	}
+
+	if tx.Version != expectedVersion {
 		return coreerr.E("checkTxVersion",
-			fmt.Sprintf("version %d invalid after HF5 at height %d", tx.Version, height),
+			fmt.Sprintf("version %d invalid at height %d (expected %d)", tx.Version, height, expectedVersion),
 			ErrTxVersionInvalid)
 	}
 
-	if !hf5Active && tx.Version >= types.VersionPostHF5 {
-		return coreerr.E("checkTxVersion",
-			fmt.Sprintf("version %d not allowed before HF5 at height %d", tx.Version, height),
-			ErrTxVersionInvalid)
-	}
-
-	if hf5Active && tx.HardforkID != currentFork {
+	if tx.Version >= types.VersionPostHF5 && tx.HardforkID != currentFork {
 		return coreerr.E("checkTxVersion",
 			fmt.Sprintf("hardfork id %d does not match active fork %d at height %d", tx.HardforkID, currentFork, height),
 			ErrTxVersionInvalid)

consensus/tx_version_test.go

@@ -79,8 +79,18 @@ func TestCheckTxVersion_Bad(t *testing.T) {
 		forks  []config.HardFork
 		height uint64
 	}{
+		// v0 regular transaction before HF4 — must still be v1.
+		{"v0_before_hf4", func() *types.Transaction {
+			tx := validV1Tx()
+			tx.Version = types.VersionInitial
+			return tx
+		}(), config.MainnetForks, 5000},
+		// v1 transaction after HF4 — must be v2.
+		{"v1_after_hf4", validV1Tx(), config.TestnetForks, 150},
 		// v2 transaction after HF5 — must be v3.
 		{"v2_after_hf5", validV2Tx(), config.TestnetForks, 250},
+		// v3 transaction after HF4 but before HF5 — too early.
+		{"v3_after_hf4_before_hf5", validV3Tx(), config.TestnetForks, 150},
 		// v3 transaction after HF5 with wrong hardfork id.
 		{"v3_after_hf5_wrong_hardfork", func() *types.Transaction {
 			tx := validV3Tx()
@@ -108,9 +118,23 @@ func TestCheckTxVersion_Bad(t *testing.T) {
 }
 
 func TestCheckTxVersion_Ugly(t *testing.T) {
+	// v2 at exact HF4 activation boundary (height 101 on testnet, HF4.Height=100).
+	txHF4 := validV2Tx()
+	err := checkTxVersion(txHF4, config.TestnetForks, 101)
+	if err != nil {
+		t.Errorf("v2 at HF4 activation boundary should be valid: %v", err)
+	}
+
+	// v1 at exact HF4 activation boundary should be rejected.
+	txPreHF4 := validV1Tx()
+	err = checkTxVersion(txPreHF4, config.TestnetForks, 101)
+	if err == nil {
+		t.Error("v1 at HF4 activation boundary should be rejected")
+	}
+
 	// v3 at exact HF5 activation boundary (height 201 on testnet, HF5.Height=200).
 	tx := validV3Tx()
-	err := checkTxVersion(tx, config.TestnetForks, 201)
+	err = checkTxVersion(tx, config.TestnetForks, 201)
 	if err != nil {
 		t.Errorf("v3 at HF5 activation boundary should be valid: %v", err)
 	}