Stage 12: observability & performance (OTel/OTLP, domain metrics, guest GC)

- pkg/telemetry: shared OTel provider bootstrap (none/stdout/otlp + W3C
  propagators + Go runtime metrics); backend/internal/telemetry becomes a thin
  facade keeping its gin middleware.
- Telemetry parity: gateway and the Telegram connector gain telemetry runtimes
  and config (GATEWAY_/TELEGRAM_ SERVICE_NAME + OTEL_*); otelgrpc instruments the
  backend push server, the gateway's backend+connector clients and the connector
  server. Default exporter stays none (collector/dashboards are Stage 14).
- Operational metrics (variant attribute on game-scoped ones): game_replay_duration,
  game_move_validate_duration, games_started_total, games_abandoned_total,
  game_cache_active, chat_messages_total{kind}, gateway edge_request_duration.
  Wired via the SetMetrics setter pattern (default no-op meter).
- TODO-3: account.GuestReaper deletes guests with no game seat past
  BACKEND_GUEST_RETENTION (default 30d, swept every BACKEND_GUEST_REAP_INTERVAL).
- Tests: pkg/telemetry exporter selection; game/social/edge metric recording via
  a manual reader; config (otlp accepted, guest knobs); inttest guest reaper.
- Docs: PLAN.md re-scopes Stage 12 and adds Stage 13 (alphabet-on-wire) + Stage 14
  (CI/deploy) with the agreed dictionary-versioning resolution; ARCHITECTURE 11/13,
  TESTING, the three READMEs and FUNCTIONAL(+ru) updated.

gateway/internal/connectsrv/server.go

@@ -14,6 +14,7 @@ import (
 	"time"
 
 	"connectrpc.com/connect"
+	"go.opentelemetry.io/otel/metric"
 	"go.uber.org/zap"
 	"golang.org/x/net/http2"
 	"golang.org/x/net/http2/h2c"
@@ -39,6 +40,7 @@ type Server struct {
 	heartbeat  time.Duration
 	log        *zap.Logger
 	adminProxy http.Handler
+	metrics    *serverMetrics
 
 	publicPolicy ratelimit.Policy
 	userPolicy   ratelimit.Policy
@@ -55,6 +57,7 @@ type Deps struct {
 	Heartbeat  time.Duration
 	Logger     *zap.Logger
 	AdminProxy http.Handler
+	Meter      metric.Meter
 }
 
 // NewServer constructs the edge service.
@@ -71,6 +74,7 @@ func NewServer(d Deps) *Server {
 		heartbeat:    d.Heartbeat,
 		log:          log,
 		adminProxy:   d.AdminProxy,
+		metrics:      newServerMetrics(d.Meter),
 		publicPolicy: ratelimit.PerMinute(d.RateLimit.PublicPerMinute, d.RateLimit.PublicBurst),
 		userPolicy:   ratelimit.PerMinute(d.RateLimit.UserPerMinute, d.RateLimit.UserBurst),
 		emailPolicy:  ratelimit.Per(d.RateLimit.EmailPer10Min, 10*time.Minute, d.RateLimit.EmailBurst),
@@ -95,9 +99,14 @@ func (s *Server) HTTPHandler() http.Handler {
 // (result_code != "ok", HTTP 200); only edge failures (rate limit, missing
 // session, unknown type, internal) become Connect errors.
 func (s *Server) Execute(ctx context.Context, req *connect.Request[edgev1.ExecuteRequest]) (*connect.Response[edgev1.ExecuteResponse], error) {
+	start := time.Now()
 	msgType := req.Msg.GetMessageType()
+	result := "internal"
+	defer func() { s.metrics.recordEdge(ctx, msgType, result, start) }()
+
 	op, ok := s.registry.Lookup(msgType)
 	if !ok {
+		result = "unknown_type"
 		return nil, connect.NewError(connect.CodeNotFound, errUnknownMessageType(msgType))
 	}
 	clientIP := peerIP(req.Peer().Addr, req.Header())
@@ -106,17 +115,21 @@ func (s *Server) Execute(ctx context.Context, req *connect.Request[edgev1.Execut
 	if op.Auth {
 		uid, err := s.resolve(ctx, req.Header())
 		if err != nil {
+			result = "unauthenticated"
 			return nil, err
 		}
 		if !s.limiter.Allow("user:"+uid, s.userPolicy) {
+			result = "rate_limited"
 			return nil, connect.NewError(connect.CodeResourceExhausted, errRateLimited)
 		}
 		tr.UserID = uid
 	} else {
 		if !s.limiter.Allow("ip:"+clientIP, s.publicPolicy) {
+			result = "rate_limited"
 			return nil, connect.NewError(connect.CodeResourceExhausted, errRateLimited)
 		}
 		if op.Email && !s.limiter.Allow("email:"+clientIP, s.emailPolicy) {
+			result = "rate_limited"
 			return nil, connect.NewError(connect.CodeResourceExhausted, errRateLimited)
 		}
 	}
@@ -124,6 +137,7 @@ func (s *Server) Execute(ctx context.Context, req *connect.Request[edgev1.Execut
 	payload, err := op.Handler(ctx, tr)
 	if err != nil {
 		if code, domain := transcode.DomainCode(err); domain {
+			result = "domain"
 			return connect.NewResponse(&edgev1.ExecuteResponse{
 				RequestId:  req.Msg.GetRequestId(),
 				ResultCode: code,
@@ -132,6 +146,7 @@ func (s *Server) Execute(ctx context.Context, req *connect.Request[edgev1.Execut
 		s.log.Error("execute failed", zap.String("message_type", msgType), zap.Error(err))
 		return nil, connect.NewError(connect.CodeInternal, errInternal)
 	}
+	result = "ok"
 	return connect.NewResponse(&edgev1.ExecuteResponse{
 		RequestId:  req.Msg.GetRequestId(),
 		ResultCode: "ok",