test(config): cover RegisterChannelSettings hook

Unit tests prove an out-of-tree channel type becomes valid and decodable after
RegisterChannelSettings, including the full InitChannelList -> GetDecoded path that
previously failed with "unknown type".

pkg/config/register_channel_settings_test.go

@@ -0,0 +1,54 @@
+package config
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+// customChannelSettings stands in for an out-of-tree channel's settings struct.
+type customChannelSettings struct {
+	Token string `json:"token"`
+}
+
+// TestRegisterChannelSettings verifies the public registration hook makes a
+// previously-unknown channel type valid and decodable — the behavior out-of-tree
+// channels rely on (they call RegisterChannelSettings from init()).
+func TestRegisterChannelSettings(t *testing.T) {
+	const typ = "custom_test_channel"
+
+	assert.False(t, isValidChannelType(typ), "type should be unknown before registration")
+
+	RegisterChannelSettings(typ, customChannelSettings{})
+
+	assert.True(t, isValidChannelType(typ), "type should be valid after registration")
+
+	got := newChannelSettings(typ)
+	_, ok := got.(*customChannelSettings)
+	assert.Truef(t, ok, "newChannelSettings(%q) = %T, want *customChannelSettings", typ, got)
+}
+
+// TestRegisterChannelSettings_InitChannelList verifies that a config carrying a
+// registered out-of-tree channel type passes InitChannelList and decodes its
+// settings — the full path that previously errored with "unknown type".
+func TestRegisterChannelSettings_InitChannelList(t *testing.T) {
+	const typ = "custom_initlist_channel"
+	RegisterChannelSettings(typ, customChannelSettings{})
+
+	channels := ChannelsConfig{
+		"mychan": {
+			Type:     typ,
+			Enabled:  true,
+			Settings: RawNode(`{"token":"secret-123"}`),
+		},
+	}
+
+	require.NoError(t, InitChannelList(channels))
+
+	decoded, err := channels["mychan"].GetDecoded()
+	require.NoError(t, err)
+	cfg, ok := decoded.(*customChannelSettings)
+	require.True(t, ok)
+	assert.Equal(t, "secret-123", cfg.Token)
+}