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/protocol3_test.go

@@ -41,6 +41,7 @@ func configWithDir(t testing.TB, host string, port int, callsign, authKey string
 		"callsign":       callsign,
 		"authKey":        authKey,
 		"talkGroup":      talkGroup,
+		"protocol":       "v3",
 		"certificateDir": certDir,
 		"enableLogging":  false,
 		"logFile":        logPath,
@@ -509,7 +510,7 @@ func TestCADigestMismatchIsLoggedAndKept(t *testing.T) {
 	}
 	body, err := jsonv2.Marshal(map[string]any{
 		"host": "127.0.0.1", "port": refl.port, "callsign": "DL1ABC", "authKey": "key",
-		"talkGroup": 20, "certificateDir": certDir, "enableLogging": true, "logFile": logPath,
+		"talkGroup": 20, "protocol": "v3", "certificateDir": certDir, "enableLogging": true, "logFile": logPath,
 	})
 	if err != nil {
 		t.Fatal(err)