feat(payments): Telegram Stars payment rail

Accept real money via Telegram Stars (XTR) — the third intake rail
alongside Robokassa (direct) and VK Votes.

Only the bot reaches Telegram, so the rail funnels through the reverse
mTLS bot-link:
- the gateway mints the invoice on a CreateInvoice command (the bot
  calls createInvoiceLink, XTR; the link goes to WebApp.openInvoice);
- the bot gates each pre_checkout_query via a ValidatePreCheckout unary
  (the order must exist, be still creditable and not already paid — the
  reusable-invoice double-pay guard; the decline reason is localised to
  the order account's language);
- a completed successful_payment is queued in a durable pure-Go SQLite
  outbox and forwarded via a ForwardPayment unary, credited once
  (idempotent on telegram_payment_charge_id, honours an expired order),
  re-driven on restart and every 30s.

The rail is wired by TELEGRAM_STARS_OUTBOX_DIR (default /data) but stays
inert until a chip pack carries an XTR price, so seeding a Stars price in
the admin is the go-live.

Tests: backend integration (order->forward->credit once, duplicate,
pre_checkout gate) + bot outbox unit (idempotent, restart re-drive) +
executor createInvoice. Docs: PAYMENTS(+ru) §9, ARCHITECTURE, the
platform/telegram README, PLAN.

platform/telegram/internal/botlink/executor_test.go

@@ -13,11 +13,13 @@ import (
 
 // fakeSender records the delivery calls the executor makes.
 type fakeSender struct {
-	notify  []notifyCall
-	text    []textCall
-	gate    []gateCall
-	applied bool // ApplyChatGate's reported result
-	err     error
+	notify      []notifyCall
+	text        []textCall
+	gate        []gateCall
+	invoice     []invoiceCall
+	invoiceLink string // CreateInvoiceLink's returned link
+	applied     bool   // ApplyChatGate's reported result
+	err         error
 }
 
 type notifyCall struct {
@@ -32,6 +34,10 @@ type gateCall struct {
 	userID int64
 	allow  bool
 }
+type invoiceCall struct {
+	title, description, payload string
+	amount                      int64
+}
 
 func (f *fakeSender) Notify(_ context.Context, chatID int64, text, buttonText, startParam string) error {
 	f.notify = append(f.notify, notifyCall{chatID, text, buttonText, startParam})
@@ -48,6 +54,11 @@ func (f *fakeSender) ApplyChatGate(_ context.Context, userID int64, allow bool)
 	return f.applied, f.err
 }
 
+func (f *fakeSender) CreateInvoiceLink(_ context.Context, title, description, payload string, amountStars int64) (string, error) {
+	f.invoice = append(f.invoice, invoiceCall{title, description, payload, amountStars})
+	return f.invoiceLink, f.err
+}
+
 func yourTurnPayload(gameID string) []byte {
 	b := flatbuffers.NewBuilder(0)
 	gid := b.CreateString(gameID)
@@ -67,7 +78,7 @@ func TestExecutorNotifyDelivers(t *testing.T) {
 	const gameID = "7c9e6679-7425-40de-944b-e07fc1f90ae7"
 	sender := &fakeSender{}
 	exec := NewExecutor(sender, 0, nil)
-	delivered, err := exec.Handle(context.Background(), notifyCmd("12345", "your_turn", yourTurnPayload(gameID), "en"))
+	delivered, _, err := exec.Handle(context.Background(), notifyCmd("12345", "your_turn", yourTurnPayload(gameID), "en"))
 	if err != nil {
 		t.Fatalf("handle: %v", err)
 	}
@@ -85,7 +96,7 @@ func TestExecutorNotifyDelivers(t *testing.T) {
 func TestExecutorNotifySkipsUnrenderedKind(t *testing.T) {
 	sender := &fakeSender{}
 	exec := NewExecutor(sender, 0, nil)
-	delivered, err := exec.Handle(context.Background(), notifyCmd("12345", "opponent_moved", nil, "en"))
+	delivered, _, err := exec.Handle(context.Background(), notifyCmd("12345", "opponent_moved", nil, "en"))
 	if err != nil {
 		t.Fatalf("handle: %v", err)
 	}
@@ -99,7 +110,7 @@ func TestExecutorNotifySkipsUnrenderedKind(t *testing.T) {
 
 func TestExecutorNotifyInvalidExternalID(t *testing.T) {
 	exec := NewExecutor(&fakeSender{}, 0, nil)
-	if _, err := exec.Handle(context.Background(), notifyCmd("not-a-number", "your_turn", yourTurnPayload("g"), "en")); err == nil {
+	if _, _, err := exec.Handle(context.Background(), notifyCmd("not-a-number", "your_turn", yourTurnPayload("g"), "en")); err == nil {
 		t.Error("expected an error for a non-numeric external_id")
 	}
 }
@@ -108,7 +119,7 @@ func TestExecutorSendToUser(t *testing.T) {
 	sender := &fakeSender{}
 	exec := NewExecutor(sender, 0, nil)
 	cmd := &botlinkv1.Command{Payload: &botlinkv1.Command_SendToUser{SendToUser: &telegramv1.SendToUserRequest{ExternalId: "999", Text: "hi"}}}
-	delivered, err := exec.Handle(context.Background(), cmd)
+	delivered, _, err := exec.Handle(context.Background(), cmd)
 	if err != nil {
 		t.Fatalf("handle: %v", err)
 	}
@@ -126,7 +137,7 @@ func chatGateCmd(externalID string, allow bool) *botlinkv1.Command {
 func TestExecutorChatGateApplied(t *testing.T) {
 	sender := &fakeSender{applied: true}
 	exec := NewExecutor(sender, 0, nil)
-	delivered, err := exec.Handle(context.Background(), chatGateCmd("777", true))
+	delivered, _, err := exec.Handle(context.Background(), chatGateCmd("777", true))
 	if err != nil {
 		t.Fatalf("handle: %v", err)
 	}
@@ -138,7 +149,7 @@ func TestExecutorChatGateApplied(t *testing.T) {
 func TestExecutorChatGateNotInChat(t *testing.T) {
 	sender := &fakeSender{applied: false} // user not in the chat
 	exec := NewExecutor(sender, 0, nil)
-	delivered, err := exec.Handle(context.Background(), chatGateCmd("888", false))
+	delivered, _, err := exec.Handle(context.Background(), chatGateCmd("888", false))
 	if err != nil {
 		t.Fatalf("handle: %v", err)
 	}
@@ -152,24 +163,53 @@ func TestExecutorChatGateNotInChat(t *testing.T) {
 
 func TestExecutorChatGateInvalidExternalID(t *testing.T) {
 	exec := NewExecutor(&fakeSender{}, 0, nil)
-	if _, err := exec.Handle(context.Background(), chatGateCmd("not-a-number", true)); err == nil {
+	if _, _, err := exec.Handle(context.Background(), chatGateCmd("not-a-number", true)); err == nil {
 		t.Error("expected an error for a non-numeric external_id")
 	}
 }
 
+func TestExecutorCreateInvoice(t *testing.T) {
+	sender := &fakeSender{invoiceLink: "https://t.me/$abc"}
+	exec := NewExecutor(sender, 0, nil)
+	cmd := &botlinkv1.Command{Payload: &botlinkv1.Command_CreateInvoice{CreateInvoice: &botlinkv1.CreateInvoiceCommand{
+		Title: "50 chips", Description: "50 chips", Payload: "order-1", Amount: 40,
+	}}}
+	delivered, result, err := exec.Handle(context.Background(), cmd)
+	if err != nil {
+		t.Fatalf("handle: %v", err)
+	}
+	if !delivered || result != "https://t.me/$abc" {
+		t.Errorf("create invoice = %v / %q, want true / the link", delivered, result)
+	}
+	if len(sender.invoice) != 1 || sender.invoice[0].payload != "order-1" || sender.invoice[0].amount != 40 {
+		t.Errorf("invoice calls = %+v", sender.invoice)
+	}
+}
+
+func TestExecutorCreateInvoiceError(t *testing.T) {
+	sender := &fakeSender{err: context.DeadlineExceeded}
+	exec := NewExecutor(sender, 0, nil)
+	cmd := &botlinkv1.Command{Payload: &botlinkv1.Command_CreateInvoice{CreateInvoice: &botlinkv1.CreateInvoiceCommand{
+		Title: "x", Description: "x", Payload: "order-2", Amount: 10,
+	}}}
+	if _, _, err := exec.Handle(context.Background(), cmd); err == nil {
+		t.Error("expected an error when minting the invoice fails")
+	}
+}
+
 func TestExecutorSendToChannel(t *testing.T) {
 	channelCmd := &botlinkv1.Command{Payload: &botlinkv1.Command_SendToChannel{SendToChannel: &telegramv1.SendToGameChannelRequest{Text: "news"}}}
 
 	t.Run("unconfigured", func(t *testing.T) {
 		exec := NewExecutor(&fakeSender{}, 0, nil)
-		if _, err := exec.Handle(context.Background(), channelCmd); err == nil {
+		if _, _, err := exec.Handle(context.Background(), channelCmd); err == nil {
 			t.Error("expected an error when no channel is configured")
 		}
 	})
 	t.Run("configured", func(t *testing.T) {
 		sender := &fakeSender{}
 		exec := NewExecutor(sender, 555, nil)
-		delivered, err := exec.Handle(context.Background(), channelCmd)
+		delivered, _, err := exec.Handle(context.Background(), channelCmd)
 		if err != nil {
 			t.Fatalf("handle: %v", err)
 		}