fix(buzz): restore relay-driven NIP-42 subscription

pkg/channels/buzz/buzz.go

@@ -24,6 +24,8 @@ import (
 // kindStreamMessage is the Buzz chat message kind (NIP-29 style).
 const kindStreamMessage = 9
 
+const subscribeTimeout = 15 * time.Second
+
 // BuzzChannel implements the Channel interface for a Buzz relay.
 type BuzzChannel struct {
 	*channels.BaseChannel
@@ -169,6 +171,60 @@ func (c *BuzzChannel) Start(ctx context.Context) error {
 	return nil
 }
 
+// subscribeAuthed subscribes, performing the NIP-42 handshake if the relay
+// demands it. The relay rejection establishes that its challenge has been
+// received by go-nostr before Auth signs the response.
+func (c *BuzzChannel) subscribeAuthed(
+	ctx context.Context,
+	filters nostr.Filters,
+) (*nostr.Subscription, error) {
+	sub, err := c.relay.Subscribe(ctx, filters)
+	if err != nil {
+		return nil, fmt.Errorf("buzz subscribe failed: %w", err)
+	}
+
+	select {
+	case <-ctx.Done():
+		return nil, ctx.Err()
+	case <-sub.EndOfStoredEvents:
+		return sub, nil
+	case reason := <-sub.ClosedReason:
+		if !strings.HasPrefix(reason, "auth-required") {
+			return nil, fmt.Errorf("buzz relay closed subscription: %s", reason)
+		}
+		sub.Unsub()
+		if err := c.relay.Auth(ctx, func(evt *nostr.Event) error {
+			return evt.Sign(c.secretKey)
+		}); err != nil {
+			return nil, fmt.Errorf("buzz NIP-42 auth failed: %w", err)
+		}
+		logger.InfoCF("buzz", "Authenticated to relay", map[string]any{
+			"relay": c.config.RelayURL, "pubkey": c.publicKey,
+		})
+
+		authed, err := c.relay.Subscribe(ctx, filters)
+		if err != nil {
+			return nil, fmt.Errorf("buzz subscribe after auth failed: %w", err)
+		}
+		const postAuthGrace = 3 * time.Second
+		select {
+		case <-ctx.Done():
+			return nil, ctx.Err()
+		case <-authed.EndOfStoredEvents:
+			return authed, nil
+		case reason := <-authed.ClosedReason:
+			return nil, fmt.Errorf("buzz relay rejected subscription after auth: %s", reason)
+		case <-time.After(postAuthGrace):
+			logger.InfoCF("buzz", "Subscription accepted after auth (no EOSE)", map[string]any{
+				"relay": c.config.RelayURL,
+			})
+			return authed, nil
+		}
+	case <-time.After(subscribeTimeout):
+		return nil, fmt.Errorf("buzz timed out waiting for relay to accept subscription")
+	}
+}
+
 // Stop closes the subscription and disconnects from the relay.
 func (c *BuzzChannel) Stop(ctx context.Context) error {
 	logger.InfoC("buzz", "Stopping Buzz channel")