feat(config): add HardforkActivationHeight helper

Returns the raw activation height for a given hardfork version.
Needed by the pre-hardfork transaction freeze logic.

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

config/hardfork.go

@@ -93,3 +93,15 @@ func IsHardForkActive(forks []HardFork, version uint8, height uint64) bool {
 	}
 	return false
 }
+
+// HardforkActivationHeight returns the activation height for the given
+// hardfork version. The fork becomes active at heights strictly greater
+// than the returned value. Returns (0, false) if the version is not found.
+func HardforkActivationHeight(forks []HardFork, version uint8) (uint64, bool) {
+	for _, hf := range forks {
+		if hf.Version == version {
+			return hf.Height, true
+		}
+	}
+	return 0, false
+}

config/hardfork_activation_test.go

@@ -0,0 +1,49 @@
+// Copyright (c) 2017-2026 Lethean (https://lt.hn)
+//
+// Licensed under the European Union Public Licence (EUPL) version 1.2.
+// SPDX-License-Identifier: EUPL-1.2
+
+package config
+
+import "testing"
+
+func TestHardforkActivationHeight_Good(t *testing.T) {
+	tests := []struct {
+		name    string
+		forks   []HardFork
+		version uint8
+		want    uint64
+		wantOK  bool
+	}{
+		{"mainnet_hf5", MainnetForks, HF5, 999999999, true},
+		{"testnet_hf5", TestnetForks, HF5, 200, true},
+		{"testnet_hf4", TestnetForks, HF4Zarcanum, 100, true},
+		{"mainnet_hf0", MainnetForks, HF0Initial, 0, true},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got, ok := HardforkActivationHeight(tt.forks, tt.version)
+			if ok != tt.wantOK {
+				t.Fatalf("HardforkActivationHeight ok = %v, want %v", ok, tt.wantOK)
+			}
+			if got != tt.want {
+				t.Errorf("HardforkActivationHeight = %d, want %d", got, tt.want)
+			}
+		})
+	}
+}
+
+func TestHardforkActivationHeight_Bad(t *testing.T) {
+	_, ok := HardforkActivationHeight(MainnetForks, 99)
+	if ok {
+		t.Error("HardforkActivationHeight with unknown version should return false")
+	}
+}
+
+func TestHardforkActivationHeight_Ugly(t *testing.T) {
+	_, ok := HardforkActivationHeight(nil, HF5)
+	if ok {
+		t.Error("HardforkActivationHeight with nil forks should return false")
+	}
+}