feat(email): PWA login sends code only; drop admin link from alert emails

Two email changes, per the owner:

1. Code-only login from an installed PWA. A login requested while running as a
   standalone PWA now omits the one-tap confirm link from the email — the link
   would open in a separate browser whose minted session cannot reach the PWA,
   stranding the login. The code is typed in the same window instead. The client
   sends a `pwa` flag (isStandalone) on the email-code request (a new FBS field,
   threaded through the gateway); the backend omits the deeplink when it is set,
   reusing the existing deletion-code link-omission path. Non-PWA browser logins
   keep the one-tap link. No polling, no migration.

2. Security: the operator alert digest no longer embeds the admin-console (/_gm)
   URL. An admin link must never travel in an email, where a mail provider could
   cache or index it; the operator opens the console directly.

Tests: an inttest asserting the PWA login email omits the link (and a browser one
keeps it); a codec round-trip of the new pwa field; the alert-digest test flipped
to guard the admin link is absent. Docs: ARCHITECTURE + FUNCTIONAL (+ru).

backend/cmd/backend/main.go

@@ -12,7 +12,6 @@ import (
 	"fmt"
 	"log"
 	"os/signal"
-	"strings"
 	"syscall"
 	"time"
 
@@ -216,11 +215,9 @@ func run(ctx context.Context, cfg config.Config, logger *zap.Logger) error {
 	// Operator alert emails on new feedback / word complaints, coalesced into one digest
 	// per interval. Inert unless a distinct admin sender and recipient are configured.
 	if cfg.SMTP.AdminFrom != "" && cfg.SMTP.AdminTo != "" {
-		consoleURL := ""
-		if cfg.PublicBaseURL != "" {
-			consoleURL = strings.TrimRight(cfg.PublicBaseURL, "/") + "/_gm"
-		}
-		alerts := adminalert.New(mailer, feedbackSvc, games, cfg.SMTP.AdminFrom, cfg.SMTP.AdminTo, consoleURL, logger)
+		// The alert digest carries no admin-console link on purpose — an admin URL must not
+		// travel in an email (a mail provider could cache or index it); see adminalert.New.
+		alerts := adminalert.New(mailer, feedbackSvc, games, cfg.SMTP.AdminFrom, cfg.SMTP.AdminTo, logger)
 		go alerts.Run(ctx, adminAlertInterval)
 		logger.Info("admin alert worker started", zap.Duration("interval", adminAlertInterval))
 	}

backend/internal/account/email.go

@@ -105,9 +105,10 @@ func (s *EmailService) allowSend(email string) bool {
 
 // issueCode generates a fresh confirm-code and one-tap deeplink token for (accountID,
 // email), replaces any prior pending confirmation, and mails the branded code in
-// locale; purpose selects the email wording and what verifying does. Only the SHA-256
-// hashes of the code and token are stored.
-func (s *EmailService) issueCode(ctx context.Context, accountID uuid.UUID, email, purpose, locale string) error {
+// locale; purpose selects the email wording and what verifying does. omitLink drops the
+// one-tap deeplink from the email (account deletion, or a login requested from an installed
+// PWA). Only the SHA-256 hashes of the code and token are stored.
+func (s *EmailService) issueCode(ctx context.Context, accountID uuid.UUID, email, purpose, locale string, omitLink bool) error {
 	code, codeHash, err := generateCode()
 	if err != nil {
 		return err
@@ -119,11 +120,12 @@ func (s *EmailService) issueCode(ctx context.Context, accountID uuid.UUID, email
 	if err := s.store.replacePendingConfirmation(ctx, accountID, email, codeHash, tokenHash, purpose, s.now().Add(emailCodeTTL)); err != nil {
 		return err
 	}
-	// Account deletion is never a one-tap link (a prefetch or a stray click must not delete
-	// an account): the delete code is entered in the app only, so the email omits the
-	// deeplink and ConfirmByToken refuses a delete token.
+	// Omit the one-tap deeplink when asked: for a login from an installed PWA (the link would
+	// open in a separate browser whose minted session cannot reach the PWA), or for account
+	// deletion (a prefetch or stray click must not delete an account — the delete code is entered
+	// in the app only, and ConfirmByToken refuses a delete token).
 	deeplink := s.confirmURL(token, locale)
-	if purpose == purposeDelete {
+	if purpose == purposeDelete || omitLink {
 		deeplink = ""
 	}
 	msg, err := renderConfirmationEmail(purpose, code, deeplink, s.baseURL, locale)
@@ -175,7 +177,7 @@ func (s *EmailService) RequestCode(ctx context.Context, accountID uuid.UUID, ema
 		}
 		return ErrEmailTaken
 	}
-	return s.issueCode(ctx, accountID, addr, purposeLink, s.accountLocale(ctx, accountID))
+	return s.issueCode(ctx, accountID, addr, purposeLink, s.accountLocale(ctx, accountID), false)
 }
 
 // ConfirmCode verifies code for accountID and email. On success it attaches a
@@ -221,8 +223,11 @@ func (s *EmailService) ConfirmCode(ctx context.Context, accountID uuid.UUID, ema
 // the ordinary returning-user login. The code is mailed to the address, so only its
 // real owner can complete the login. On first contact browserTZ (the client's
 // detected "±HH:MM" UTC offset) seeds the new account's time zone and language its UI
-// language. It returns the target account id for the subsequent LoginWithCode.
-func (s *EmailService) RequestLoginCode(ctx context.Context, email, browserTZ, language string) (uuid.UUID, error) {
+// language. When pwa is set (the request came from an installed PWA) the login email omits the
+// one-tap confirm link — it would open in a separate browser, out of the PWA's reach — so the
+// code is entered in the same window. It returns the target account id for the subsequent
+// LoginWithCode.
+func (s *EmailService) RequestLoginCode(ctx context.Context, email, browserTZ, language string, pwa bool) (uuid.UUID, error) {
 	addr, err := normalizeEmail(email)
 	if err != nil {
 		return uuid.UUID{}, err
@@ -234,7 +239,7 @@ func (s *EmailService) RequestLoginCode(ctx context.Context, email, browserTZ, l
 	if err != nil {
 		return uuid.UUID{}, err
 	}
-	if err := s.issueCode(ctx, acc.ID, addr, purposeLogin, language); err != nil {
+	if err := s.issueCode(ctx, acc.ID, addr, purposeLogin, language, pwa); err != nil {
 		return uuid.UUID{}, err
 	}
 	return acc.ID, nil

backend/internal/account/link.go

@@ -92,7 +92,7 @@ func (s *EmailService) RequestLinkCode(ctx context.Context, accountID uuid.UUID,
 	if !s.allowSend(addr) {
 		return ErrTooManyRequests
 	}
-	return s.issueCode(ctx, accountID, addr, purposeLink, s.accountLocale(ctx, accountID))
+	return s.issueCode(ctx, accountID, addr, purposeLink, s.accountLocale(ctx, accountID), false)
 }
 
 // ConfirmLink verifies code for (accountID, email) and reports the address's
@@ -140,7 +140,7 @@ func (s *EmailService) RequestChangeCode(ctx context.Context, accountID uuid.UUI
 	if !s.allowSend(addr) {
 		return ErrTooManyRequests
 	}
-	return s.issueCode(ctx, accountID, addr, purposeChange, s.accountLocale(ctx, accountID))
+	return s.issueCode(ctx, accountID, addr, purposeChange, s.accountLocale(ctx, accountID), false)
 }
 
 // ConfirmChange verifies code for (accountID, newEmail) and atomically replaces the
@@ -199,7 +199,7 @@ func (s *EmailService) RequestDeleteCode(ctx context.Context, accountID uuid.UUI
 	if !s.allowSend(addr) {
 		return ErrTooManyRequests
 	}
-	return s.issueCode(ctx, accountID, addr, purposeDelete, s.accountLocale(ctx, accountID))
+	return s.issueCode(ctx, accountID, addr, purposeDelete, s.accountLocale(ctx, accountID), false)
 }
 
 // VerifyDeleteCode verifies the account-deletion code against the account's own email and

backend/internal/adminalert/notify.go

@@ -33,21 +33,21 @@ type Notifier struct {
 	complaints ComplaintCounter
 	from       string
 	to         string
-	consoleURL string
 	clock      func() time.Time
 	log        *zap.Logger
 	last       time.Time
 }
 
-// New constructs a Notifier. from and to are the alert sender and recipient(s); consoleURL,
-// when non-empty, is the admin-console link included in the email. log may be nil. The
-// watermark starts at "now", so only items arriving after start-up are reported.
-func New(mailer account.Mailer, fb FeedbackCounter, cp ComplaintCounter, from, to, consoleURL string, log *zap.Logger) *Notifier {
+// New constructs a Notifier. from and to are the alert sender and recipient(s); log may be
+// nil. The watermark starts at "now", so only items arriving after start-up are reported. The
+// digest deliberately carries no admin-console link — an admin URL must never travel in an
+// email, where a mail provider could cache or index it.
+func New(mailer account.Mailer, fb FeedbackCounter, cp ComplaintCounter, from, to string, log *zap.Logger) *Notifier {
 	if log == nil {
 		log = zap.NewNop()
 	}
 	return &Notifier{
-		mailer: mailer, feedback: fb, complaints: cp, from: from, to: to, consoleURL: consoleURL,
+		mailer: mailer, feedback: fb, complaints: cp, from: from, to: to,
 		clock: func() time.Time { return time.Now().UTC() }, log: log, last: time.Now().UTC(),
 	}
 }
@@ -103,10 +103,9 @@ func (n *Notifier) digest(fb, cp int) account.Message {
 		parts = append(parts, fmt.Sprintf("%d new word complaint(s)", cp))
 	}
 	summary := strings.Join(parts, ", ")
+	// No admin-console link in the body: an admin URL must never travel in an email (a mail
+	// provider could cache or index it). The operator opens the console directly.
 	text := summary + "."
-	if n.consoleURL != "" {
-		text += "\n\nOpen the admin console: " + n.consoleURL
-	}
 	return account.Message{
 		From:    n.from,
 		To:      n.to,

backend/internal/adminalert/notify_test.go

@@ -28,7 +28,7 @@ func (m *recordingMailer) Send(_ context.Context, msg account.Message) error {
 
 func TestNotifierSkipsWhenNothingNew(t *testing.T) {
 	mailer := &recordingMailer{}
-	n := New(mailer, fbCounter{0}, cpCounter{0}, "alerts@erudit-game.ru", "op@x.ru", "", nil)
+	n := New(mailer, fbCounter{0}, cpCounter{0}, "alerts@erudit-game.ru", "op@x.ru", nil)
 	n.tick(context.Background())
 	if len(mailer.sent) != 0 {
 		t.Fatalf("sent %d emails, want 0 when nothing is new", len(mailer.sent))
@@ -37,7 +37,7 @@ func TestNotifierSkipsWhenNothingNew(t *testing.T) {
 
 func TestNotifierDigestsNewItems(t *testing.T) {
 	mailer := &recordingMailer{}
-	n := New(mailer, fbCounter{2}, cpCounter{1}, "alerts@erudit-game.ru", "op@x.ru, two@x.ru", "https://erudit-game.ru/_gm", nil)
+	n := New(mailer, fbCounter{2}, cpCounter{1}, "alerts@erudit-game.ru", "op@x.ru, two@x.ru", nil)
 	n.tick(context.Background())
 	if len(mailer.sent) != 1 {
 		t.Fatalf("sent %d emails, want 1 digest", len(mailer.sent))
@@ -49,7 +49,9 @@ func TestNotifierDigestsNewItems(t *testing.T) {
 	if !strings.Contains(msg.Subject, "2 new feedback") || !strings.Contains(msg.Subject, "1 new word complaint") {
 		t.Errorf("digest subject = %q, want the feedback + complaint counts", msg.Subject)
 	}
-	if !strings.Contains(msg.Text, "/_gm") {
-		t.Errorf("digest body = %q, want the console link", msg.Text)
+	// The digest must never carry an admin-console link — an admin URL in an email is a leak
+	// (mail providers cache/index it).
+	if strings.Contains(msg.Text, "/_gm") || strings.Contains(strings.ToLower(msg.Text), "admin console") {
+		t.Errorf("digest body = %q, must not carry an admin-console link", msg.Text)
 	}
 }

backend/internal/inttest/email_test.go

@@ -206,7 +206,7 @@ func TestEmailLoginFlow(t *testing.T) {
 	svc := account.NewEmailService(account.NewStore(testDB), mailer, "https://erudit-game.ru")
 	email := "login-" + uuid.NewString() + "@example.com"
 
-	accountID, err := svc.RequestLoginCode(ctx, email, "+02:00", "en")
+	accountID, err := svc.RequestLoginCode(ctx, email, "+02:00", "en", false)
 	if err != nil {
 		t.Fatalf("request login code: %v", err)
 	}
@@ -233,7 +233,7 @@ func TestEmailLoginFlow(t *testing.T) {
 	}
 
 	// A second login for the same email is the returning user: same account.
-	if _, err := svc.RequestLoginCode(ctx, email, "", "ru"); err != nil {
+	if _, err := svc.RequestLoginCode(ctx, email, "", "ru", false); err != nil {
 		t.Fatalf("second request: %v", err)
 	}
 	acc2, err := svc.LoginWithCode(ctx, email, sixDigit.FindString(mailer.lastBody))
@@ -255,7 +255,7 @@ func TestEmailLoginProvisionsGuestUntilConfirmed(t *testing.T) {
 	svc := account.NewEmailService(store, mailer, "https://erudit-game.ru")
 	email := "squat-" + uuid.NewString() + "@example.com"
 
-	id, err := svc.RequestLoginCode(ctx, email, "", "en")
+	id, err := svc.RequestLoginCode(ctx, email, "", "en", false)
 	if err != nil {
 		t.Fatalf("request login code: %v", err)
 	}
@@ -279,6 +279,34 @@ func TestEmailLoginProvisionsGuestUntilConfirmed(t *testing.T) {
 	}
 }
 
+// TestEmailLoginPWAOmitsLink: a login requested from an installed PWA (pwa=true) mails only the
+// code — no one-tap confirm link, which would otherwise open in a separate browser out of the
+// PWA's reach. A non-PWA request keeps the link.
+func TestEmailLoginPWAOmitsLink(t *testing.T) {
+	ctx := context.Background()
+	mailer := &capturingMailer{}
+	svc := account.NewEmailService(account.NewStore(testDB), mailer, "https://erudit-game.ru")
+
+	pwaEmail := "pwa-login-" + uuid.NewString() + "@example.com"
+	if _, err := svc.RequestLoginCode(ctx, pwaEmail, "", "en", true); err != nil {
+		t.Fatalf("pwa request login: %v", err)
+	}
+	if sixDigit.FindString(mailer.lastBody) == "" {
+		t.Errorf("pwa login mail must still carry the code, body %q", mailer.lastBody)
+	}
+	if confirmToken.MatchString(mailer.lastBody) {
+		t.Errorf("pwa login mail must omit the one-tap confirm link, body %q", mailer.lastBody)
+	}
+
+	webEmail := "web-login-" + uuid.NewString() + "@example.com"
+	if _, err := svc.RequestLoginCode(ctx, webEmail, "", "en", false); err != nil {
+		t.Fatalf("web request login: %v", err)
+	}
+	if !confirmToken.MatchString(mailer.lastBody) {
+		t.Errorf("non-pwa login mail must keep the one-tap confirm link, body %q", mailer.lastBody)
+	}
+}
+
 // confirmToken extracts the one-tap deeplink token from the /app/#/confirm/<token> link
 // the branded email carries.
 var confirmToken = regexp.MustCompile(`/confirm/([A-Za-z0-9_-]+)`)
@@ -301,7 +329,7 @@ func TestConfirmByTokenLogin(t *testing.T) {
 	svc := account.NewEmailService(store, mailer, "https://erudit-game.ru")
 	email := "tok-login-" + uuid.NewString() + "@example.com"
 
-	id, err := svc.RequestLoginCode(ctx, email, "", "en")
+	id, err := svc.RequestLoginCode(ctx, email, "", "en", false)
 	if err != nil {
 		t.Fatalf("request login: %v", err)
 	}
@@ -382,7 +410,7 @@ func TestEmailAccountSeedsDisplayName(t *testing.T) {
 	svc := account.NewEmailService(store, &capturingMailer{}, "https://erudit-game.ru")
 	local := "kaya-" + uuid.NewString()[:8]
 
-	id, err := svc.RequestLoginCode(ctx, local+"@example.com", "", "en")
+	id, err := svc.RequestLoginCode(ctx, local+"@example.com", "", "en", false)
 	if err != nil {
 		t.Fatalf("request login: %v", err)
 	}

backend/internal/server/handlers_auth.go

@@ -174,6 +174,10 @@ type emailRequest struct {
 	Email     string `json:"email"`
 	BrowserTZ string `json:"browser_tz"`
 	Language  string `json:"language"`
+	// Pwa marks a request from an installed PWA (standalone display mode): the login email then
+	// omits the one-tap confirm link so the code is typed in the same window (the link would open
+	// in a separate browser whose session cannot reach the PWA). See EmailService.RequestLoginCode.
+	Pwa bool `json:"pwa"`
 }
 
 // handleEmailRequest issues a login confirm-code to the email. It always reports
@@ -185,7 +189,7 @@ func (s *Server) handleEmailRequest(c *gin.Context) {
 		abortBadRequest(c, "email is required")
 		return
 	}
-	if _, err := s.emails.RequestLoginCode(c.Request.Context(), req.Email, req.BrowserTZ, req.Language); err != nil {
+	if _, err := s.emails.RequestLoginCode(c.Request.Context(), req.Email, req.BrowserTZ, req.Language, req.Pwa); err != nil {
 		s.abortErr(c, err)
 		return
 	}