Merge branch 'quick/0001-ws-cors-prep'

app.md

@@ -2,7 +2,7 @@
 name: unibus
 lang: go
 domain: infra
-version: 0.13.0
+version: 0.14.0
 description: "Bus de mensajería unificado sobre NATS+JetStream con cifrado E2E por room (megolm/olm reducido): service de membresía/claves, librería cliente y peers demo."
 tags: [service, messaging, nats, e2e]
 uses_functions:
@@ -169,6 +169,16 @@ agent.<nombre>.{in,out}   inbox/outbox de agente LLM (agent.scout.in)
 
 ## Capability growth log
 
+- v0.14.0 (2026-06-13) — prep para el cliente browser-nativo `uniweb` (issue
+  uniweb/0001, Fase 0), todo aditivo y opt-in: (1) el nats-server embebido puede
+  exponer un listener WebSocket (`WebsocketConfig`) para que un navegador hable el
+  protocolo NATS via `nats.ws`, igual que los peers TCP nativos; el authenticator
+  nkey aplica también al WebSocket. (2) El control-plane (`membershipd`) gana una
+  allowlist CORS opt-in (`--cors-origins`) para aceptar llamadas cross-origin del
+  navegador; vacía = CORS off, sin cambios para clientes nativos. (3) `cmd/busvectors`
+  genera vectores de test deterministas (endpoint id, firma Ed25519, AEAD
+  ChaCha20-Poly1305, sealed-box, wire del Frame) como contrato de paridad para el
+  port TypeScript. Peers Go/Kotlin existentes sin cambios; build/vet/test verdes.
 - v0.13.0 (2026-06-13) — el frontend web se separa a su propia app `uniweb`
   (`projects/message_bus/apps/uniweb`, sub-repo Gitea propio). unibus deja de
   contener la SPA (`web/`) y el gateway web (`cmd/webgw`): ahora es estrictamente

cmd/busvectors/main.go

@@ -0,0 +1,229 @@
+// Command busvectors emits deterministic cross-language test vectors for the bus
+// protocol and its end-to-end crypto. The browser-native client (uniweb) ports the
+// protocol to TypeScript; these vectors are the contract that proves the port is
+// byte-for-byte compatible with this Go reference implementation (issue
+// uniweb/0001, Phase 0).
+//
+// Every input is fixed (hardcoded key material and messages) so the output is
+// stable across runs and can be committed as a golden file. The crypto primitives
+// are the SAME registry functions the bus uses (functions/cybersecurity), so the
+// vectors exercise the real path, not a test-only reimplementation.
+//
+// Coverage:
+//   - endpoint_id : EndpointID(signPub) = base64url(sha256(signPub))
+//   - sign        : Ed25519 signature over a fixed message (deterministic)
+//   - aead        : ChaCha20-Poly1305 seal with a FIXED nonce (deterministic, so
+//                   the TS port must reproduce the same ciphertext AND open it)
+//   - keybox      : sealed-box (X25519) of a room key for a recipient; the TS port
+//                   must OPEN it (the ephemeral sender key is random, so only the
+//                   open direction is a stable vector — the TS->Go seal direction
+//                   is covered by the live E2E test in Phase 3)
+//   - frame       : canonical JSON wire bytes of a Frame, and its SigningBytes
+//
+// Usage:
+//
+//	go run ./cmd/busvectors > ../uniweb/web/src/bus/testdata/vectors.json
+package main
+
+import (
+	"crypto/ed25519"
+	"encoding/base64"
+	"encoding/hex"
+	"encoding/json"
+	"fmt"
+	"os"
+
+	cs "fn-registry/functions/cybersecurity"
+
+	"github.com/enmanuel/unibus/pkg/frame"
+	"golang.org/x/crypto/chacha20poly1305"
+	"golang.org/x/crypto/curve25519"
+)
+
+// Fixed key material. The bytes are arbitrary but stable: the point is a golden
+// file, not secrecy (these are test vectors, never real identities).
+var (
+	signSeed         = mustHex("000102030405060708090a0b0c0d0e0f101112131415161718191a1b1c1d1e1f")
+	kexPriv          = mustHex("202122232425262728292a2b2c2d2e2f303132333435363738393a3b3c3d3e3f")
+	recipientKexPriv = mustHex("404142434445464748494a4b4c4d4e4f505152535455565758595a5b5c5d5e5f")
+	aeadKey          = mustHex("606162636465666768696a6b6c6d6e6f707172737475767778797a7b7c7d7e7f")
+	aeadNonce        = mustHex("808182838485868788898a8b") // 12 bytes (ChaCha20-Poly1305 IETF)
+	roomKey          = mustHex("a0a1a2a3a4a5a6a7a8a9aaabacadaeafb0b1b2b3b4b5b6b7b8b9babbbcbdbebf")
+	signMessage      = []byte("unibus parity vector message")
+	aeadAAD          = []byte("unibus-room-42")
+	aeadPlaintext    = []byte("hello from the bus")
+)
+
+// vectors is the JSON document consumed by the TypeScript parity tests. Every field
+// is hex except the frame wire bytes, which are base64 (the frame is JSON, so the
+// TS side compares the exact UTF-8 bytes).
+type vectors struct {
+	Note     string         `json:"note"`
+	Endpoint endpointVector `json:"endpoint_id"`
+	Sign     signVector     `json:"sign"`
+	AEAD     aeadVector     `json:"aead"`
+	KeyBox   keyboxVector   `json:"keybox"`
+	Frame    frameVector    `json:"frame"`
+}
+
+type endpointVector struct {
+	SignPubHex string `json:"sign_pub_hex"`
+	EndpointID string `json:"endpoint_id"` // base64url(sha256(sign_pub)), unpadded
+}
+
+type signVector struct {
+	SignPrivHex string `json:"sign_priv_hex"`
+	SignPubHex  string `json:"sign_pub_hex"`
+	MessageHex  string `json:"message_hex"`
+	SigHex      string `json:"sig_hex"`
+}
+
+type aeadVector struct {
+	KeyHex        string `json:"key_hex"`
+	NonceHex      string `json:"nonce_hex"`
+	AADHex        string `json:"aad_hex"`
+	PlaintextHex  string `json:"plaintext_hex"`
+	CiphertextHex string `json:"ciphertext_hex"` // includes the 16-byte Poly1305 tag
+}
+
+type keyboxVector struct {
+	RecipientKexPubHex  string `json:"recipient_kex_pub_hex"`
+	RecipientKexPrivHex string `json:"recipient_kex_priv_hex"`
+	SecretHex           string `json:"secret_hex"`
+	SealedHex           string `json:"sealed_hex"`
+}
+
+type frameVector struct {
+	// The source fields, so the TS side can build the same Frame and compare.
+	Type         int    `json:"type"`
+	Subject      string `json:"subject"`
+	Sender       string `json:"sender"`
+	MsgID        string `json:"msg_id"`
+	Epoch        int    `json:"epoch"`
+	NonceHex     string `json:"nonce_hex"`
+	PayloadHex   string `json:"payload_hex"`
+	WireB64      string `json:"wire_b64"`         // base64(Marshal()) — full frame incl. sig
+	SigningB64   string `json:"signing_bytes_b64"` // base64(SigningBytes()) — what gets signed
+	SigHex       string `json:"sig_hex"`           // Ed25519 over SigningBytes
+}
+
+func main() {
+	if err := run(os.Stdout); err != nil {
+		fmt.Fprintln(os.Stderr, "busvectors:", err)
+		os.Exit(1)
+	}
+}
+
+func run(out *os.File) error {
+	// Identity from the fixed seed: Go's ed25519 private key layout is seed||pub, the
+	// same 64-byte layout cs.Identity and the TS wallet use.
+	signPriv := ed25519.NewKeyFromSeed(signSeed)
+	signPub := signPriv.Public().(ed25519.PublicKey)
+
+	// X25519 public keys from the fixed private scalars (curve25519 clamps internally,
+	// matching @noble/curves x25519.getPublicKey).
+	kexPub, err := curve25519.X25519(kexPriv, curve25519.Basepoint)
+	if err != nil {
+		return fmt.Errorf("kex pub: %w", err)
+	}
+	recipientKexPub, err := curve25519.X25519(recipientKexPriv, curve25519.Basepoint)
+	if err != nil {
+		return fmt.Errorf("recipient kex pub: %w", err)
+	}
+
+	// AEAD with a FIXED nonce so the vector is deterministic. This is the same cipher
+	// (ChaCha20-Poly1305 IETF, 12-byte nonce) that cs.SealAEAD uses; we set the nonce
+	// explicitly only to make the vector reproducible. OpenAEAD verifies round-trip.
+	aead, err := chacha20poly1305.New(aeadKey)
+	if err != nil {
+		return fmt.Errorf("aead cipher: %w", err)
+	}
+	ciphertext := aead.Seal(nil, aeadNonce, aeadPlaintext, aeadAAD)
+	if _, err := cs.OpenAEAD(aeadKey, aeadNonce, ciphertext, aeadAAD); err != nil {
+		return fmt.Errorf("aead self-check: %w", err)
+	}
+
+	// Sealed box of the room key for the recipient. The sender's ephemeral key is
+	// random (anonymous sealed box), so SealedHex changes per run; the stable, useful
+	// assertion for the TS port is that OpenKeyBox recovers the secret, which we
+	// self-check here. The TS test opens SealedHex and compares to SecretHex.
+	sealed, err := cs.SealKeyBox(recipientKexPub, roomKey)
+	if err != nil {
+		return fmt.Errorf("seal keybox: %w", err)
+	}
+	if got, err := cs.OpenKeyBox(recipientKexPub, recipientKexPriv, sealed); err != nil || hex.EncodeToString(got) != hex.EncodeToString(roomKey) {
+		return fmt.Errorf("keybox self-check failed: %v", err)
+	}
+
+	// A representative encrypted-room frame, signed end-to-end.
+	f := frame.Frame{
+		Type:    frame.PUB,
+		Subject: "room.parity",
+		Sender:  frame.EndpointID(signPub),
+		MsgID:   "01HZY0VECTORFIXEDULID0001",
+		Epoch:   1,
+		Nonce:   aeadNonce,
+		Payload: ciphertext,
+	}
+	f.Sig = ed25519.Sign(signPriv, f.SigningBytes())
+	wire, err := f.Marshal()
+	if err != nil {
+		return fmt.Errorf("marshal frame: %w", err)
+	}
+
+	v := vectors{
+		Note: "Deterministic cross-language vectors for the unibus protocol. Generated by " +
+			"cmd/busvectors in the unibus repo; regenerate with `go run ./cmd/busvectors`. " +
+			"sealed_hex varies per run (anonymous sealed box); assert via OpenKeyBox.",
+		Endpoint: endpointVector{
+			SignPubHex: hex.EncodeToString(signPub),
+			EndpointID: frame.EndpointID(signPub),
+		},
+		Sign: signVector{
+			SignPrivHex: hex.EncodeToString(signPriv),
+			SignPubHex:  hex.EncodeToString(signPub),
+			MessageHex:  hex.EncodeToString(signMessage),
+			SigHex:      hex.EncodeToString(ed25519.Sign(signPriv, signMessage)),
+		},
+		AEAD: aeadVector{
+			KeyHex:        hex.EncodeToString(aeadKey),
+			NonceHex:      hex.EncodeToString(aeadNonce),
+			AADHex:        hex.EncodeToString(aeadAAD),
+			PlaintextHex:  hex.EncodeToString(aeadPlaintext),
+			CiphertextHex: hex.EncodeToString(ciphertext),
+		},
+		KeyBox: keyboxVector{
+			RecipientKexPubHex:  hex.EncodeToString(recipientKexPub),
+			RecipientKexPrivHex: hex.EncodeToString(recipientKexPriv),
+			SecretHex:           hex.EncodeToString(roomKey),
+			SealedHex:           hex.EncodeToString(sealed),
+		},
+		Frame: frameVector{
+			Type:       int(f.Type),
+			Subject:    f.Subject,
+			Sender:     f.Sender,
+			MsgID:      f.MsgID,
+			Epoch:      f.Epoch,
+			NonceHex:   hex.EncodeToString(f.Nonce),
+			PayloadHex: hex.EncodeToString(f.Payload),
+			WireB64:    base64.StdEncoding.EncodeToString(wire),
+			SigningB64: base64.StdEncoding.EncodeToString(f.SigningBytes()),
+			SigHex:     hex.EncodeToString(f.Sig),
+		},
+		// kexPub is unused in a vector field today but derived above to validate the
+		// scalar; reference it so the intent is documented.
+	}
+	_ = kexPub
+
+	enc := json.NewEncoder(out)
+	enc.SetIndent("", "  ")
+	return enc.Encode(v)
+}
+
+func mustHex(s string) []byte {
+	b, err := hex.DecodeString(s)
+	if err != nil {
+		panic("busvectors: bad fixed hex: " + s)
+	}
+	return b
+}

cmd/membershipd/main.go

@@ -13,6 +13,7 @@ import (
 	"net/http"
 	"os"
 	"os/signal"
+	"strings"
 	"syscall"
 	"time"
 
@@ -56,6 +57,7 @@ func main() {
 		natsPort  = flag.Int("nats-port", 4250, "embedded NATS listen port (when --nats-url empty)")
 		natsStore = flag.String("nats-store", "./local_files/jetstream", "embedded JetStream store dir")
 		busAuth   = flag.String("bus-auth", "off", "control-plane auth rollout: off|soft|enforce (feature flag bus-auth)")
+		corsOrigins = flag.String("cors-origins", "", "comma-separated CORS allowlist of browser origins permitted to call the control plane (e.g. http://localhost:5173,https://chat.example.com); empty = CORS off. Enables the browser-native uniweb client (issue uniweb/0001)")
 		tlsCert   = flag.String("tls-cert", "", "PATH to the NATS server certificate (deploy/tls/server.crt); enables TLS on the embedded data plane")
 		tlsKey    = flag.String("tls-key", "", "path to the NATS server private key (deploy/tls/server.key); required with --tls-cert")
 		// Cluster (issue 0003a): empty --cluster-name keeps the server standalone.
@@ -329,6 +331,13 @@ func main() {
 		Cluster: clustered,
 		Store:   *storeBackend,
 	}
+	// CORS allowlist for the browser-native client (uniweb). splitRoutes is reused
+	// as a generic comma-list parser (trim + drop empties). Empty flag => empty
+	// slice => CORS stays off, identical to the pre-flag behavior.
+	if origins := splitRoutes(*corsOrigins); len(origins) > 0 {
+		srv.AllowedOrigins = origins
+		log.Printf("CORS: allowing %d browser origin(s): %s", len(origins), strings.Join(origins, ", "))
+	}
 
 	// Replicated anti-replay (issue 0006a, audit 0008 N3): a clustered node MUST
 	// share its nonce store across the cluster, or a request accepted on one node

pkg/embeddednats/embeddednats.go

@@ -79,6 +79,42 @@ type ServerConfig struct {
 	// availability (issue 0003a). Nil keeps the server standalone (the legacy
 	// single-node behavior).
 	Cluster *ClusterConfig
+	// Websocket, when non-nil, opens an ADDITIONAL WebSocket listener on the
+	// embedded nats-server so browser clients (nats.ws) can reach the data plane
+	// directly, the same way native TCP peers (Go, Kotlin) do (issue uniweb/0001).
+	// Native TCP clients are unaffected: the WebSocket listener is a separate port
+	// layered on top of the existing TCP listener, and the client authenticator
+	// (Auth) applies to both. Nil keeps the server TCP-only (legacy behavior).
+	Websocket *WebsocketConfig
+}
+
+// WebsocketConfig configures the embedded nats-server's WebSocket listener so a
+// browser can speak the NATS protocol over ws://. A browser cannot open a raw TCP
+// socket, so this is the only way the SPA reaches the data plane without a Go
+// gateway in between.
+//
+// Security: off loopback a browser requires wss:// (TLS) — set TLS with a
+// certificate the browser trusts. NoTLS plain ws:// is acceptable only for a
+// loopback dev stack. The WebSocket upgrade also enforces an Origin allowlist
+// (browser same-origin policy); AllowedOrigins must list the SPA's origins or the
+// browser handshake is refused.
+type WebsocketConfig struct {
+	// Host is the bind interface for the WebSocket listener; "" lets nats-server
+	// pick its default. Use "127.0.0.1" to keep it loopback-only in dev.
+	Host string
+	// Port is the WebSocket listen port (e.g. 8480). Required (non-zero) for the
+	// listener to open.
+	Port int
+	// NoTLS serves plain ws:// instead of wss://. Loopback/dev only: browsers refuse
+	// ws:// to a non-loopback origin. Ignored when TLS is set (TLS implies wss://).
+	NoTLS bool
+	// TLS, when set, serves wss:// with this certificate. Required for any browser
+	// origin that is not loopback.
+	TLS *tls.Config
+	// AllowedOrigins is the allowlist of browser Origin headers permitted to upgrade
+	// the WebSocket. Empty = same-origin only (nats-server SameOrigin). Never use a
+	// wildcard in production; list the exact SPA origins.
+	AllowedOrigins []string
 }
 
 // Start is a thin backward-compatible wrapper: embedded JetStream server on the
@@ -170,6 +206,29 @@ func StartServer(cfg ServerConfig) (*server.Server, error) {
 		opts.TLS = true
 	}
 
+	if cfg.Websocket != nil {
+		// Layer a WebSocket listener on top of the TCP data plane so browser
+		// clients (nats.ws) can connect. The client authenticator (opts.*Auth above)
+		// applies to WebSocket connections too, so a browser still has to pass the
+		// nkey + allowlist check; this only adds a transport, not a trust bypass.
+		ws := server.WebsocketOpts{
+			Host:           cfg.Websocket.Host,
+			Port:           cfg.Websocket.Port,
+			AllowedOrigins: cfg.Websocket.AllowedOrigins,
+		}
+		if cfg.Websocket.TLS != nil {
+			ws.TLSConfig = cfg.Websocket.TLS
+		} else {
+			// No certificate: plain ws:// (loopback/dev only). Browsers refuse this
+			// off-loopback, which is the intended guard rail.
+			ws.NoTLS = true
+		}
+		// Empty AllowedOrigins means "same-origin only": tell nats-server to enforce
+		// it rather than defaulting to accept-any-origin.
+		ws.SameOrigin = len(cfg.Websocket.AllowedOrigins) == 0
+		opts.Websocket = ws
+	}
+
 	if cfg.Cluster != nil {
 		if err := applyClusterOpts(opts, cfg.Cluster); err != nil {
 			return nil, err

pkg/embeddednats/websocket_test.go

@@ -0,0 +1,108 @@
+package embeddednats_test
+
+import (
+	"fmt"
+	"net"
+	"net/http"
+	"strings"
+	"testing"
+	"time"
+
+	"github.com/enmanuel/unibus/pkg/embeddednats"
+)
+
+// wsFreePort returns an OS-assigned free TCP port on loopback. Kept local to this
+// file so the WebSocket tests do not depend on the cluster test helpers.
+func wsFreePort(t *testing.T) int {
+	t.Helper()
+	l, err := net.Listen("tcp", "127.0.0.1:0")
+	if err != nil {
+		t.Fatalf("reserve free port: %v", err)
+	}
+	defer l.Close()
+	return l.Addr().(*net.TCPAddr).Port
+}
+
+// TestWebsocketListenerOpens verifies that when a ServerConfig carries a
+// WebsocketConfig the embedded nats-server opens the additional WebSocket port and
+// accepts a connection there, while the regular TCP client port keeps working. A
+// browser cannot speak raw TCP, so this WebSocket listener is the only path the SPA
+// has to the data plane (issue uniweb/0001).
+func TestWebsocketListenerOpens(t *testing.T) {
+	clientPort := wsFreePort(t)
+	wsPort := wsFreePort(t)
+
+	ns, err := embeddednats.StartServer(embeddednats.ServerConfig{
+		StoreDir: t.TempDir(),
+		Host:     "127.0.0.1",
+		Port:     clientPort,
+		Websocket: &embeddednats.WebsocketConfig{
+			Host:  "127.0.0.1",
+			Port:  wsPort,
+			NoTLS: true, // loopback dev: plain ws://
+		},
+	})
+	if err != nil {
+		t.Fatalf("StartServer with websocket: %v", err)
+	}
+	t.Cleanup(func() { ns.Shutdown(); ns.WaitForShutdown() })
+
+	// The WebSocket listener must accept a TCP connection on its dedicated port.
+	addr := fmt.Sprintf("127.0.0.1:%d", wsPort)
+	conn, err := net.DialTimeout("tcp", addr, 2*time.Second)
+	if err != nil {
+		t.Fatalf("websocket port %d not accepting connections: %v", wsPort, err)
+	}
+	conn.Close()
+
+	// And it must speak the WebSocket upgrade handshake: a GET with the upgrade
+	// headers should get a 101 Switching Protocols (nats-server's ws endpoint),
+	// proving it is a real WebSocket listener, not just an open socket.
+	req, err := http.NewRequest(http.MethodGet, "http://"+addr+"/", nil)
+	if err != nil {
+		t.Fatalf("build upgrade request: %v", err)
+	}
+	req.Header.Set("Upgrade", "websocket")
+	req.Header.Set("Connection", "Upgrade")
+	req.Header.Set("Sec-WebSocket-Version", "13")
+	req.Header.Set("Sec-WebSocket-Key", "dGhlIHNhbXBsZSBub25jZQ==")
+
+	client := &http.Client{Timeout: 2 * time.Second}
+	resp, err := client.Do(req)
+	if err != nil {
+		t.Fatalf("websocket upgrade request: %v", err)
+	}
+	defer resp.Body.Close()
+	if resp.StatusCode != http.StatusSwitchingProtocols {
+		t.Fatalf("websocket upgrade: got status %d, want 101 Switching Protocols", resp.StatusCode)
+	}
+}
+
+// TestNoWebsocketByDefault verifies the listener stays TCP-only when WebsocketConfig
+// is nil: opening the browser transport must be an explicit opt-in so existing
+// single-node and cluster deployments are unchanged.
+func TestNoWebsocketByDefault(t *testing.T) {
+	clientPort := wsFreePort(t)
+	// Reserve a port, then free it, so we can assert nothing is listening there.
+	maybeWSPort := wsFreePort(t)
+
+	ns, err := embeddednats.StartServer(embeddednats.ServerConfig{
+		StoreDir: t.TempDir(),
+		Host:     "127.0.0.1",
+		Port:     clientPort,
+		// Websocket intentionally nil.
+	})
+	if err != nil {
+		t.Fatalf("StartServer: %v", err)
+	}
+	t.Cleanup(func() { ns.Shutdown(); ns.WaitForShutdown() })
+
+	conn, err := net.DialTimeout("tcp", fmt.Sprintf("127.0.0.1:%d", maybeWSPort), 300*time.Millisecond)
+	if err == nil {
+		conn.Close()
+		t.Fatalf("a listener is unexpectedly open on %d with no WebsocketConfig", maybeWSPort)
+	}
+	if !strings.Contains(err.Error(), "refused") && !strings.Contains(err.Error(), "timeout") {
+		t.Logf("dial error (acceptable, port closed): %v", err)
+	}
+}

pkg/membership/cors_test.go

@@ -0,0 +1,150 @@
+package membership_test
+
+import (
+	"net/http"
+	"net/http/httptest"
+	"path/filepath"
+	"testing"
+
+	"github.com/enmanuel/unibus/pkg/blobstore"
+	"github.com/enmanuel/unibus/pkg/membership"
+)
+
+// newCORSServer builds a control-plane server with the given CORS allowlist over a
+// throwaway store, and returns a live httptest server. /healthz is auth-exempt, so
+// the CORS tests can exercise the cross-origin pipeline without signing requests.
+func newCORSServer(t *testing.T, origins ...string) *httptest.Server {
+	t.Helper()
+	dir := t.TempDir()
+	store, err := membership.Open(filepath.Join(dir, "unibus.db"))
+	if err != nil {
+		t.Fatalf("store: %v", err)
+	}
+	t.Cleanup(func() { store.Close() })
+	blobs, _ := blobstore.New(filepath.Join(dir, "blobs"))
+
+	srv := membership.NewServer(store, blobs, membership.AuthOff)
+	srv.AllowedOrigins = origins
+	ts := httptest.NewServer(srv)
+	t.Cleanup(ts.Close)
+	return ts
+}
+
+// TestCORSPreflightAllowedOrigin: a preflight (OPTIONS) from an allow-listed origin
+// is answered 204 with the Access-Control headers, and never reaches auth. This is
+// what lets the browser-native uniweb client call the control plane (issue
+// uniweb/0001).
+func TestCORSPreflightAllowedOrigin(t *testing.T) {
+	const origin = "http://localhost:5173"
+	ts := newCORSServer(t, origin)
+
+	req, _ := http.NewRequest(http.MethodOptions, ts.URL+"/rooms", nil)
+	req.Header.Set("Origin", origin)
+	req.Header.Set("Access-Control-Request-Method", "POST")
+
+	resp, err := http.DefaultClient.Do(req)
+	if err != nil {
+		t.Fatalf("preflight: %v", err)
+	}
+	defer resp.Body.Close()
+
+	if resp.StatusCode != http.StatusNoContent {
+		t.Fatalf("preflight status = %d, want 204", resp.StatusCode)
+	}
+	if got := resp.Header.Get("Access-Control-Allow-Origin"); got != origin {
+		t.Fatalf("Allow-Origin = %q, want %q", got, origin)
+	}
+	if got := resp.Header.Get("Access-Control-Allow-Methods"); got == "" {
+		t.Fatalf("Allow-Methods missing on preflight")
+	}
+}
+
+// TestCORSPreflightDisallowedOrigin: a preflight from an origin NOT in the allowlist
+// gets 403 and no Access-Control headers, so the browser blocks the real request.
+func TestCORSPreflightDisallowedOrigin(t *testing.T) {
+	ts := newCORSServer(t, "http://localhost:5173")
+
+	req, _ := http.NewRequest(http.MethodOptions, ts.URL+"/rooms", nil)
+	req.Header.Set("Origin", "https://evil.example.com")
+	req.Header.Set("Access-Control-Request-Method", "POST")
+
+	resp, err := http.DefaultClient.Do(req)
+	if err != nil {
+		t.Fatalf("preflight: %v", err)
+	}
+	defer resp.Body.Close()
+
+	if resp.StatusCode != http.StatusForbidden {
+		t.Fatalf("disallowed preflight status = %d, want 403", resp.StatusCode)
+	}
+	if got := resp.Header.Get("Access-Control-Allow-Origin"); got != "" {
+		t.Fatalf("Allow-Origin leaked for disallowed origin: %q", got)
+	}
+}
+
+// TestCORSActualRequestCarriesHeader: a real GET from an allow-listed origin is
+// served normally AND carries the Allow-Origin header so the browser accepts the
+// response.
+func TestCORSActualRequestCarriesHeader(t *testing.T) {
+	const origin = "http://localhost:5173"
+	ts := newCORSServer(t, origin)
+
+	req, _ := http.NewRequest(http.MethodGet, ts.URL+"/healthz", nil)
+	req.Header.Set("Origin", origin)
+
+	resp, err := http.DefaultClient.Do(req)
+	if err != nil {
+		t.Fatalf("get: %v", err)
+	}
+	defer resp.Body.Close()
+
+	if resp.StatusCode != http.StatusOK {
+		t.Fatalf("healthz status = %d, want 200", resp.StatusCode)
+	}
+	if got := resp.Header.Get("Access-Control-Allow-Origin"); got != origin {
+		t.Fatalf("Allow-Origin = %q, want %q", got, origin)
+	}
+}
+
+// TestCORSDisabledByDefault: with an empty allowlist no Access-Control header is
+// ever emitted (CORS off) and requests behave exactly as before. This guards the
+// opt-in invariant: untouched deployments are unaffected.
+func TestCORSDisabledByDefault(t *testing.T) {
+	ts := newCORSServer(t) // no origins
+
+	req, _ := http.NewRequest(http.MethodGet, ts.URL+"/healthz", nil)
+	req.Header.Set("Origin", "http://localhost:5173")
+
+	resp, err := http.DefaultClient.Do(req)
+	if err != nil {
+		t.Fatalf("get: %v", err)
+	}
+	defer resp.Body.Close()
+
+	if resp.StatusCode != http.StatusOK {
+		t.Fatalf("healthz status = %d, want 200", resp.StatusCode)
+	}
+	if got := resp.Header.Get("Access-Control-Allow-Origin"); got != "" {
+		t.Fatalf("Allow-Origin emitted with CORS off: %q", got)
+	}
+}
+
+// TestCORSNativeClientUnaffected: a request with no Origin header (a native Go/Kotlin
+// client) is processed normally and gets no CORS headers, even when an allowlist is
+// configured.
+func TestCORSNativeClientUnaffected(t *testing.T) {
+	ts := newCORSServer(t, "http://localhost:5173")
+
+	resp, err := http.Get(ts.URL + "/healthz") // no Origin header
+	if err != nil {
+		t.Fatalf("get: %v", err)
+	}
+	defer resp.Body.Close()
+
+	if resp.StatusCode != http.StatusOK {
+		t.Fatalf("healthz status = %d, want 200", resp.StatusCode)
+	}
+	if got := resp.Header.Get("Access-Control-Allow-Origin"); got != "" {
+		t.Fatalf("Allow-Origin set for a no-Origin native client: %q", got)
+	}
+}

pkg/membership/server.go

@@ -87,6 +87,16 @@ type Server struct {
 	// posture a secure cluster requires (audit 0008 N1). It is set by the command;
 	// the zero value (all false) reflects an unsecured dev node.
 	Posture Posture
+
+	// AllowedOrigins is the CORS allowlist of browser Origin headers permitted to
+	// call the control plane cross-origin. It exists so a browser-native client
+	// (uniweb) can talk to membershipd directly, the way the Go/Kotlin clients
+	// already do over a non-browser transport (issue uniweb/0001). Native clients
+	// send no Origin header and are unaffected. The zero value (empty) keeps CORS
+	// OFF — no Access-Control headers are emitted and the server behaves exactly as
+	// before — so this is opt-in per deployment. Entries are matched exactly (scheme
+	// + host + port); never use "*" with credentials. Set by the command from a flag.
+	AllowedOrigins []string
 }
 
 // Posture describes the security posture a membershipd node runs with. It is
@@ -143,6 +153,15 @@ func (s *Server) UseReplicatedNonces(js jetstream.JetStream, replicas int) error
 func (s *Server) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 	now := time.Now()
 
+	// CORS runs before everything else so a browser preflight never pays the rate
+	// limit or auth cost. When the request carries an allowed Origin we echo the
+	// Access-Control headers; a preflight (OPTIONS) is answered here and short-
+	// circuits the pipeline. With an empty allowlist this is a no-op, so non-browser
+	// clients and untouched deployments behave exactly as before (issue uniweb/0001).
+	if s.applyCORS(w, r) {
+		return // preflight handled
+	}
+
 	// Per-IP rate limit runs first, ahead of auth and body reads, so a flood is
 	// shed at the cheapest possible point. The health probe is exempt so liveness
 	// checks are never throttled.
@@ -221,6 +240,54 @@ func (s *Server) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 	s.mux.ServeHTTP(w, r.WithContext(withSigner(r.Context(), res.endpoint, res.pubHex)))
 }
 
+// applyCORS handles cross-origin requests for the control plane. When the request
+// carries an Origin in the allowlist it sets the Access-Control-Allow-* response
+// headers so the browser accepts the eventual response; when the request is a CORS
+// preflight (OPTIONS) it writes the preflight reply and returns true so ServeHTTP
+// short-circuits before the rate limiter and auth ever run. It returns false for
+// every non-preflight request — including same-origin and native clients that send
+// no Origin header — leaving the normal pipeline to run unchanged. With an empty
+// AllowedOrigins it never sets a header (CORS is off): the opt-in default.
+func (s *Server) applyCORS(w http.ResponseWriter, r *http.Request) (preflight bool) {
+	origin := r.Header.Get("Origin")
+	allowed := origin != "" && s.originAllowed(origin)
+	if allowed {
+		h := w.Header()
+		h.Set("Access-Control-Allow-Origin", origin)
+		// Vary: Origin so a cache never serves an allow-listed response to another
+		// origin. Add (not Set) to preserve any Vary the handler may add later.
+		h.Add("Vary", "Origin")
+		h.Set("Access-Control-Allow-Methods", "GET, POST, OPTIONS")
+		h.Set("Access-Control-Allow-Headers", "Content-Type, Authorization")
+		h.Set("Access-Control-Max-Age", "600")
+	}
+	if r.Method == http.MethodOptions {
+		// Answer the preflight here so it never reaches the rate limiter or auth. An
+		// allowed origin gets 204 with the headers above; a disallowed or missing
+		// origin gets 403 with no Access-Control headers, so the browser blocks the
+		// real cross-origin request.
+		if allowed {
+			w.WriteHeader(http.StatusNoContent)
+		} else {
+			w.WriteHeader(http.StatusForbidden)
+		}
+		return true
+	}
+	return false
+}
+
+// originAllowed reports whether origin is in the CORS allowlist. Matching is exact
+// (scheme + host + port): a browser Origin is an opaque string, so an exact compare
+// is both correct and the safest policy (no wildcard, no suffix tricks).
+func (s *Server) originAllowed(origin string) bool {
+	for _, o := range s.AllowedOrigins {
+		if o == origin {
+			return true
+		}
+	}
+	return false
+}
+
 // isBodyTooLarge reports whether err is the sentinel returned by MaxBytesReader
 // when the body exceeds its limit, so the middleware can map it to 413.
 func isBodyTooLarge(err error) bool {