peer: read PeerManualPortKey setting alongside RADIANCE_PEER_EXTERNAL_PORT

Adds settings.PeerManualPortKey so the user-facing Advanced UI can
persist the manual port forward without an env var. Resolution order
in peer.Client.Start's NewForwarder:

  1. settings.PeerManualPortKey (Advanced UI in lantern Flutter)
  2. RADIANCE_PEER_EXTERNAL_PORT env var (developer / power-user)
  3. UPnP discovery (default)

The setting is wired through lantern-core's
PatchSettings(PeerShareEnabledKey...) path on a separate branch — the
new `setPeerManualPort` FFI export over there calls
PatchSettings({PeerManualPortKey: <int>}) which lands in radiance's
settings store and gets picked up on the next peer.Client.Start.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: 2 people

common/settings/settings.go

@@ -56,6 +56,13 @@ const (
 	AdBlockKey          _key = "ad_block"           // bool
 	AutoConnectKey      _key = "auto_connect"       // bool
 	PeerShareEnabledKey _key = "peer_share_enabled" // bool
+	// PeerManualPortKey is the TCP port number the user has manually
+	// forwarded on their router (single-port 1:1 NAT). When non-zero,
+	// peer.Client.Start uses portforward.ManualForwarder with this port
+	// instead of probing UPnP. Surfaced as an Advanced setting in the
+	// Share My Connection UI for users on networks where UPnP is
+	// disabled or unavailable.
+	PeerManualPortKey _key = "peer_manual_port" // int (0 = use UPnP)
 	SelectedServerKey   _key = "selected_server"    // [servers.Server] Server.Options is not stored
 
 	PreferredLocationKey _key = "preferred_location" // [common.PreferredLocation]

peer/peer.go

@@ -17,6 +17,7 @@ import (
 	box "github.com/getlantern/lantern-box"
 	"github.com/getlantern/lantern-box/tracker/peerconn"
 	"github.com/getlantern/radiance/common/env"
+	"github.com/getlantern/radiance/common/settings"
 	"github.com/getlantern/radiance/events"
 	"github.com/getlantern/radiance/portforward"
 )
@@ -204,9 +205,28 @@ func NewClient(cfg Config) (*Client, error) {
 	}
 	if cfg.NewForwarder == nil {
 		cfg.NewForwarder = func(ctx context.Context) (portForwarder, error) {
+			// Manual port-forward override. Use case: networks where
+			// UPnP is disabled or unavailable (router has UPnP off for
+			// security, ISP-provided gateways without IGD, networks
+			// behind double-NAT) but the user has manually configured
+			// a port forward on their router. We trust the user's
+			// config — no UPnP roundtrip — and report the configured
+			// port as both the external and internal port (the 1:1
+			// case every consumer router exposes).
+			//
+			// Resolution order:
+			//   1. settings.PeerManualPortKey (Advanced UI)
+			//   2. RADIANCE_PEER_EXTERNAL_PORT env var (developer /
+			//      power-user override)
+			//   3. fall through to UPnP discovery
+			if port := uint16(settings.GetInt(settings.PeerManualPortKey)); port != 0 {
+				slog.Info("peer client using manual port forward",
+					"port", port, "source", "setting")
+				return &manualPortForwarder{port: port}, nil
+			}
 			if p := manualPort(); p != 0 {
 				slog.Info("peer client using manual port forward",
-					"port", p, "env", env.PeerExternalPort.String())
+					"port", p, "source", env.PeerExternalPort.String())
 				return &manualPortForwarder{port: p}, nil
 			}
 			// Explicitly return a nil interface on error — `return