feat(multiplayer): add degraded admission mode

docs/MATCHMAKING.md

@@ -411,6 +411,12 @@ Minimum controls:
   WebSocket handshake/message/idle limits, bounded fan-out and overload
   shedding. In degraded mode reject new login/queue/allocation work while
   preserving result ingestion and all live matches.
+
+  The control-plane implements the admission portion of this policy with
+  `--degraded` at startup, `SIGUSR1` to enable it, and `SIGUSR2` to disable it.
+  The gate rejects new login, queue, and proposal mutations with `503
+  service_degraded`; assignment reads, events, server registration/results,
+  health, metrics, and other live-match paths remain available.
 - Images pinned by digest, SBOM generation, dependency/image scanning, signed
   releases, admission-time signature verification, and a critical-patch SLA.
 - Structured audit events for auth, queue transitions, allocation, roster

multiplayer-next.md

@@ -1191,7 +1191,7 @@ the local/CI/community transport, not a silent production fallback.
 | 8.9 `[D:8.4,8.7]` | **IN PROGRESS.** Pure Go join policy binds SteamID/player/match/server/team/slot/protocol/expiry, rejects duplicate roster slots, permits same-identity reclaim through backend loss and fences prior server-owned generations | `server/domain/reconnect.go` covers SteamID/server/slot binding, expiry, repeated reclaim, grace boundary and old-generation fencing; signed token issuance/verification, persistent leases, Godot `hello` transport and production integration remain |
 | 8.10 `[D:8.5,8.31]` | **IN PROGRESS.** Dependency-free workload credential policy validates an adapter-verified signature, issuer/audience/time bounds, namespace/service account, pod UID, GameServer UID, allocation ID, match ID and server ID before result submission; `server/workload` now parses projected compact JWTs, rejects unsigned/malformed/ambiguous tokens, verifies signing input through an injected trust callback, and delegates exact binding to the domain policy; the API exposes the workload-authenticated server result route. **`WorkloadVerify` is now wired for real** -- the blocker this row previously named (`cmd/control-plane/main.go` never wiring it, so `/register` and `/result` 503'd on every real request) is closed by taking a different, equally-valid approach instead of the Kubernetes-JWT one: `serverMutation` only ever compares `WorkloadBinding.ServerID`/`.MatchID` (and `AdvanceServerRegistration` only additionally needs `.AllocationID`) -- nothing downstream requires Namespace/ServiceAcct/PodUID/GameServerUID, so a Kubernetes-issued token was never actually required, just the assumption that it was. `server/workload/signed_token.go` mints and verifies a short-lived HMAC-signed token with a secret only the control plane holds (the same trust model `domain.SessionStore` already uses for player sessions), needing no cluster JWKS/TokenReview to validate -- signature and expiry are fully self-contained. The token binds only `allocation_id` (deliberately, not `match_id`/`server_id` too: it must be requestable in the same Agones request that asks for a server, before Agones has picked one) -- `store.AllocationBindingByAllocationID` resolves `match_id`/`server_id` durably from the `allocations` table at verify time, so a token can never claim a pairing that wasn't actually, durably allocated. `api.WorkloadVerifierFromSignedToken` combines both and is wired into `cmd/control-plane` (`--workload-secret`/`COSMIC_CLASH_WORKLOAD_SECRET`; a startup warning fires and the route stays 503 if it's left unset) and `cmd/testkit-api` (fixed test secret). **The delivery channel is now wired too**: `agones.Client` gains `WorkloadSecret`/`WorkloadTokenTTL` -- when set, `Allocate` mints a token for the allocation and requests it as a third `cosmic-clash.io/workload-token` annotation alongside match-id/allocation-id, wired from `cmd/allocator`'s own `--workload-secret`/`COSMIC_CLASH_WORKLOAD_SECRET` (must match the control plane's); `supervisor.Supervisor.workloadToken()` resolves the bearer credential with an explicit `--workload-token-path` (kept for a possible future Kubernetes-JWT path) always winning, otherwise falling back to that same annotation -- the same fallback pattern `matchID()` already used for `cosmic-clash.io/match-id`. `WorkloadTokenPath` is accordingly no longer required at construction time | `server/domain/workload.go`, `server/workload/jwt.go`, `server/api/service.go` and adversarial tests reject every binding mutation, missing/unverified signature, `none`/malformed JWT, ambiguous audience, server/match mismatch and time boundary; `server/testkit/pipeline_test.go` carries allocation identity through the offline result path; `cmd/control-plane` now wires `ResultSubmitter: store.PostgresResults{DB: db}` (a ready-made adapter that had been referenced from nowhere at all, not even a test); `server/workload/signed_token_test.go` covers round-trip, tampered payload, wrong secret, malformed input and the exact expiry boundary; `server/api/workload_verifier_integration_test.go` (opt-in, real PostgreSQL) covers acceptance against a real allocation row, rejection of an unrecorded allocation, that two distinct real allocations each resolve to their own and only their own match/server pairing, and the previously-503 `Service.WorkloadVerify` field itself now succeeding -- all verified clean with `-race` across multiple runs; `cmd/control-plane/main_test.go`'s `TestServerRoutesRequireWorkloadVerifyToBeWired` now documents and pins the misconfigured-secret case specifically, not the "always unwired" case; `server/agones/allocation_test.go`'s `TestAllocateRequestsAWorkloadTokenAnnotationWhenConfigured` and `server/supervisor/supervisor_test.go`'s new annotation-fallback/fails-closed pair cover the delivery channel end to end (mint -> annotation -> supervisor read -> Authorization header) short of a live cluster. **What's still missing**: this has never run against a real Agones cluster (only HTTP-level fakes), so the exact `object_meta` JSON casing Agones actually returns remains unverified from this sandbox (see `GameServer.ObjectMeta`'s existing caveat); live duplicate/conflict alerting also remains |
 | 8.11 `[D:8.1]` | **DONE.** Write the threat model: forged clients/replay/queues/results, floods/bots, pod/insider compromise, gameplay and API DDoS, SDR signing-key theft, dependencies and denial-of-wallet | [`docs/THREAT-MODEL.md`](docs/THREAT-MODEL.md) records prevention, detection/response, owner and residual risk for every threat; it separates offline CA/online signer, client/game-server/PostgreSQL/Redis trust boundaries and recovery behavior |
-| 8.12 `[D:8.11]` | **IN PROGRESS.** Provider-neutral Kubernetes baseline enforces restricted namespace admission, non-root/read-only/no-capability workloads, separate service accounts, allocator-only RBAC, default-deny networking and explicit edge/data/DNS/Agones/metrics flows; application manifests consume externally populated Secret objects; the Go API and allocator now have bounded per-replica rate/quota boundaries and metrics endpoints | `deploy/k8s/base/` includes hardened control-plane, allocator, and game-server resources; `server/security/test_kubernetes_policies.py`, `server/api/rate_limit.go`, allocator metrics tests and adversarial checks cover static hardening, secret-reference invariants, fixed-window limits, bounded labels and bounded key memory; private-store provisioning, distributed/global quotas, edge DDoS/WAF/origin shielding, WebSocket limits, overload shedding, encrypted backups and live policy/load tests remain |
+| 8.12 `[D:8.11]` | **IN PROGRESS.** Provider-neutral Kubernetes baseline enforces restricted namespace admission, non-root/read-only/no-capability workloads, separate service accounts, allocator-only RBAC, default-deny networking and explicit edge/data/DNS/Agones/metrics flows; application manifests consume externally populated Secret objects; the Go API and allocator now have bounded per-replica rate/quota boundaries and metrics endpoints, plus an atomic operator-controlled degraded-mode gate that sheds new login/queue/proposal work while preserving live-match paths | `deploy/k8s/base/` includes hardened control-plane, allocator, and game-server resources; `server/security/test_kubernetes_policies.py`, `server/api/rate_limit.go`, `server/api/admission.go`, allocator metrics tests and adversarial checks cover static hardening, secret-reference invariants, fixed-window limits, bounded labels/key memory, route classification, concurrent toggling and degraded responses; start with control-plane `--degraded`, enable with SIGUSR1, disable with SIGUSR2; private-store provisioning, distributed/global quotas, edge DDoS/WAF/origin shielding, WebSocket limits, encrypted backups and live policy/load tests remain |
 | 8.13 `[D:8.12]` | **IN PROGRESS.** Docker/Kubernetes references are digest-pinned, a dependency-free checker rejects mutable tags/plaintext credentials and concrete release overlays can reject template digests; release documentation defines SBOM, dependency/image scanning, signing, admission verification and a 24-hour critical-fix SLA | `scripts/verify_supply_chain.py`, `server/security/test_supply_chain.py`, `docs/SUPPLY-CHAIN.md` and `.github/workflows/supply-chain.yml` cover repository policy and provenance requirements; registry SBOM/scan/sign/admission execution and a concrete production overlay remain |
 
 #### 8C — Queueing, matchmaking, playlists and rating

server/api/admission.go

@@ -0,0 +1,70 @@
+package api
+
+import (
+	"strings"
+	"sync/atomic"
+)
+
+// AdmissionController decides whether a classified public operation may
+// start. Implementations must be safe for concurrent requests.
+type AdmissionController interface {
+	Allow(operation string) bool
+}
+
+// AdmissionGate is the operator-controlled overload gate for new matchmaking
+// work. Degraded mode is deliberately narrow: existing matches can continue
+// to report results and clients can still use read/recovery/event endpoints.
+type AdmissionGate struct {
+	degraded atomic.Bool
+}
+
+func NewAdmissionGate(degraded bool) *AdmissionGate {
+	gate := &AdmissionGate{}
+	gate.degraded.Store(degraded)
+	return gate
+}
+
+func (g *AdmissionGate) SetDegraded(value bool) {
+	if g != nil {
+		g.degraded.Store(value)
+	}
+}
+
+func (g *AdmissionGate) Degraded() bool {
+	return g != nil && g.degraded.Load()
+}
+
+func (g *AdmissionGate) Allow(operation string) bool {
+	if !g.Degraded() {
+		return true
+	}
+	switch operation {
+	case "login", "queue", "proposal", "allocation":
+		return false
+	default:
+		return true
+	}
+}
+
+func admissionOperation(path, method string) string {
+	if method == "GET" || method == "HEAD" || method == "OPTIONS" {
+		return ""
+	}
+	path = strings.TrimSuffix(path, "/")
+	switch {
+	case path == "/v1/session/steam" || path == "/api/v1/session/steam":
+		return "login"
+	case path == "/v1/queue" || path == "/api/v1/queue/tickets":
+		return "queue"
+	case underPath(path, "/v1/queue/") || underPath(path, "/api/v1/queue/tickets/"):
+		return "queue"
+	case underPath(path, "/v1/proposals/") || underPath(path, "/api/v1/proposals/"):
+		return "proposal"
+	default:
+		return ""
+	}
+}
+
+func underPath(path, prefix string) bool {
+	return strings.HasPrefix(path, prefix) && len(path) > len(prefix)
+}

server/api/admission_test.go

@@ -0,0 +1,90 @@
+package api
+
+import (
+	"net/http"
+	"net/http/httptest"
+	"strings"
+	"sync"
+	"testing"
+)
+
+func TestAdmissionGateDefaultsToAllowAndBlocksOnlyNewWork(t *testing.T) {
+	gate := NewAdmissionGate(false)
+	for _, operation := range []string{"login", "queue", "proposal", "allocation", "result", "events"} {
+		if !gate.Allow(operation) {
+			t.Fatalf("normal mode rejected %q", operation)
+		}
+	}
+	gate.SetDegraded(true)
+	for _, operation := range []string{"login", "queue", "proposal", "allocation"} {
+		if gate.Allow(operation) {
+			t.Fatalf("degraded mode allowed %q", operation)
+		}
+	}
+	for _, operation := range []string{"result", "events", "read", ""} {
+		if !gate.Allow(operation) {
+			t.Fatalf("degraded mode rejected live-safe operation %q", operation)
+		}
+	}
+}
+
+func TestAdmissionOperationClassifiesOnlyMutations(t *testing.T) {
+	tests := []struct {
+		path, method, want string
+	}{
+		{"/v1/session/steam", http.MethodPost, "login"},
+		{"/api/v1/session/steam/", http.MethodPost, "login"},
+		{"/v1/queue", http.MethodPost, "queue"},
+		{"/api/v1/queue/tickets/abc/heartbeat", http.MethodPost, "queue"},
+		{"/v1/proposals/abc/accept", http.MethodPost, "proposal"},
+		{"/api/v1/proposals/abc", http.MethodDelete, "proposal"},
+		{"/v1/queue", http.MethodGet, ""},
+		{"/v1/queue-not-a-route", http.MethodPost, ""},
+		{"/v1/servers/abc/result", http.MethodPost, ""},
+		{"/v1/events", http.MethodPost, ""},
+	}
+	for _, test := range tests {
+		if got := admissionOperation(test.path, test.method); got != test.want {
+			t.Errorf("admissionOperation(%q, %q) = %q, want %q", test.path, test.method, got, test.want)
+		}
+	}
+}
+
+func TestAdmissionGateConcurrentToggle(t *testing.T) {
+	gate := NewAdmissionGate(false)
+	var wg sync.WaitGroup
+	for i := 0; i < 8; i++ {
+		wg.Add(1)
+		go func() {
+			defer wg.Done()
+			for j := 0; j < 1000; j++ {
+				gate.SetDegraded(j%2 == 0)
+				_ = gate.Allow("queue")
+			}
+		}()
+	}
+	wg.Wait()
+}
+
+func TestHandlerReturnsDegradedOnlyForNewMatchmakingMutations(t *testing.T) {
+	service := &Service{Admission: NewAdmissionGate(true)}
+	tests := []struct {
+		path, want string
+	}{
+		{"/v1/queue", "service_degraded"},
+		{"/api/v1/proposals/proposal-1/accept", "service_degraded"},
+		{"/v1/servers/server-1/result", "server_unavailable"},
+		{"/v1/events", ""},
+	}
+	for _, test := range tests {
+		req := httptest.NewRequest(http.MethodPost, test.path, strings.NewReader(`{}`))
+		rec := httptest.NewRecorder()
+		service.Handler().ServeHTTP(rec, req)
+		if test.want != "" && !strings.Contains(rec.Body.String(), test.want) {
+			t.Errorf("%s body = %q, want %q", test.path, rec.Body.String(), test.want)
+		}
+		if test.want == "service_degraded" && rec.Code != http.StatusServiceUnavailable {
+			t.Errorf("%s status = %d, want 503", test.path, rec.Code)
+		}
+	}
+}

server/api/service.go

@@ -127,6 +127,7 @@ type Service struct {
 	RankedProfileProvider RankedProfileProvider
 	TierPolicy            domain.TierPolicy
 	RateLimiter           *RateLimiter
+	Admission             AdmissionController
 	// Log receives a credential-safe structured event for lifecycle-relevant
 	// reads and mutations. Nil
 	// is a valid, silent no-op -- every call site must stay optional so
@@ -213,6 +214,16 @@ func (s *Service) Handler() http.Handler {
 			mux.ServeHTTP(w, r)
 		})
 	}
+	if s.Admission != nil {
+		admissionHandler := handler
+		handler = http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+			if operation := admissionOperation(r.URL.Path, r.Method); operation != "" && !s.Admission.Allow(operation) {
+				writeError(w, http.StatusServiceUnavailable, "service_degraded")
+				return
+			}
+			admissionHandler.ServeHTTP(w, r)
+		})
+	}
 	if s.Metrics == nil {
 		return handler
 	}

server/cmd/control-plane/main.go

@@ -29,6 +29,7 @@ func main() {
 	redisPrefix := flag.String("redis-prefix", envOrDefault("COSMIC_CLASH_REDIS_PREFIX", "cosmic-clash"), "Redis key prefix")
 	redisTTL := flag.Duration("redis-ttl", 60*time.Second, "TTL for transient candidate projection entries")
 	workloadSecret := flag.String("workload-secret", os.Getenv("COSMIC_CLASH_WORKLOAD_SECRET"), "HMAC secret for control-plane-issued workload tokens (see workload/signed_token.go); server registration/result submission return 503 until this is set")
+	degraded := flag.Bool("degraded", false, "start with new login, queue, and proposal mutations rejected; SIGUSR1 enables and SIGUSR2 disables this mode")
 	flag.Parse()
 	if *role != "api" {
 		fatalf("unsupported role %q (only api is implemented)", *role)
@@ -63,11 +64,28 @@ func main() {
 		fmt.Fprintln(os.Stderr, "control-plane: warning: --workload-secret / COSMIC_CLASH_WORKLOAD_SECRET is unset; server registration and result submission will return 503")
 	}
 	service := newAPIService(db, *workloadSecret, candidateIndex)
+	admission := api.NewAdmissionGate(*degraded)
+	service.Admission = admission
 	server := &http.Server{Addr: *listen, Handler: service.Handler(), ReadHeaderTimeout: 5 * time.Second}
 	serveErr := make(chan error, 1)
 	go func() { serveErr <- server.ListenAndServe() }()
 	ctx, stop := signal.NotifyContext(context.Background(), os.Interrupt, syscall.SIGTERM)
 	defer stop()
+	operatorSignals := make(chan os.Signal, 2)
+	signal.Notify(operatorSignals, syscall.SIGUSR1, syscall.SIGUSR2)
+	defer signal.Stop(operatorSignals)
+	go func() {
+		for sig := range operatorSignals {
+			switch sig {
+			case syscall.SIGUSR1:
+				admission.SetDegraded(true)
+				fmt.Fprintln(os.Stderr, "control-plane: degraded admission enabled")
+			case syscall.SIGUSR2:
+				admission.SetDegraded(false)
+				fmt.Fprintln(os.Stderr, "control-plane: degraded admission disabled")
+			}
+		}
+	}()
 	go api.RunProposalOutboxDispatcher(ctx, db, service)
 	go api.RunResultOutboxDispatcher(ctx, db, service)
 	go api.RunStateOutboxDispatcher(ctx, db, service)