Let the config choose protocol 2 or 3, and fall back for one session only.

The default stays v2. A reflector that refuses that version and names the other gets one session of it, then the station announces the configured protocol again.

Co-authored-by: Cursor <cursoragent@cursor.com>

station/behavior_test.go

@@ -49,7 +49,7 @@ func loginLog(t *testing.T, callsign, key string, tg int, id uint16, codecs []st
 		_ = st.Run(ctx)
 	}()
 	refl.accept(t)
-	declineTo2(t, refl)
+	expectVersion(t, refl, 2, 0)
 	challenge := make([]byte, 20)
 	for i := range challenge {
 		challenge[i] = byte(i + 1)
@@ -98,6 +98,14 @@ func loginLog(t *testing.T, callsign, key string, tg int, id uint16, codecs []st
 	return loggedIn{st: st, clock: clock, refl: refl, cancel: cancel, id: id, path: path}
 }
 
+func expectVersion(t *testing.T, refl *reflector, major, minor uint16) {
+	t.Helper()
+	typ, body := refl.readFrame(t)
+	if typ != 5 || !versionIs(body, major, minor) {
+		t.Fatalf("version type %d body %v, want %d.%d", typ, body, major, minor)
+	}
+}
+
 func declineTo2(t *testing.T, refl *reflector) {
 	t.Helper()
 	typ, body := refl.readFrame(t)
@@ -163,8 +171,8 @@ func TestDropRetriesUntilQuit(t *testing.T) {
 	in.clock.Advance(2 * time.Second)
 	in.refl.accept(t)
 	typ, body := in.refl.readFrame(t)
-	if typ != 5 || !versionIs(body, 3, 0) {
-		t.Fatalf("retry protocol type %d body %v, want 3.0", typ, body)
+	if typ != 5 || !versionIs(body, 2, 0) {
+		t.Fatalf("retry protocol type %d body %v, want 2.0", typ, body)
 	}
 	in.cancel()
 	in.clock.Advance(2 * time.Second)
@@ -281,7 +289,7 @@ func TestMissingOpusStopsRetries(t *testing.T) {
 		_ = st.Run(ctx)
 	}()
 	refl.accept(t)
-	declineTo2(t, refl)
+	expectVersion(t, refl, 2, 0)
 	challenge := make([]byte, 20)
 	refl.writeFrame(t, 10, appendBytes(nil, challenge))
 	refl.readFrame(t)