Take the chat client's port from Run's caller (closes #4)

The test that runs the whole bot started its stand-in chat client on
5225, the port a real simplex-chat uses, so on a machine where one
listens there the test would have sent it the bot's set-up commands.
Run now takes the chat client's port: the run command passes
bot.ChatPort (5225), and the test a port it found free.

Model: opus-5-5

internal/bot/run_test.go

@@ -52,9 +52,7 @@ func TestMain(m *testing.M) {
 // port it is given, on localhost, and answers the commands the bot
 // sends. SIGTERM ends it, as it ends the real client. Unlike the real
 // client, it also exits when the bot hangs up, so that it never
-// outlives a test run that was cut short. It takes port 5225, the chat
-// client's fixed port, so this test cannot run twice at once on one
-// machine.
+// outlives a test run that was cut short.
 func standIn() {
 	arg := func(name string) string {
 		return os.Args[slices.Index(os.Args, name)+1]
@@ -142,6 +140,8 @@ func TestStopDuringRequest(t *testing.T) {
 	t.Setenv("PATH", bin)
 
 	cfg := &config.Config{DataDir: t.TempDir(), Port: freePort(t), APIToken: credential}
+	// Never bot.ChatPort: a real chat client may be listening there.
+	chatPort := freePort(t)
 	ctx, stop := context.WithCancel(t.Context())
 	done := make(chan struct{})
 
@@ -150,7 +150,7 @@ func TestStopDuringRequest(t *testing.T) {
 	go func() {
 		defer close(done)
 
-		runErr = bot.Run(ctx, slog.New(slog.DiscardHandler), cfg)
+		runErr = bot.Run(ctx, slog.New(slog.DiscardHandler), cfg, chatPort)
 	}()
 
 	t.Cleanup(func() {