fix(worker): key rate limiter on peer IP, not forged headers

The rate limiter trusted X-Real-IP, so a client could dodge its limit by
sending a new header value on each request. It must key on the connection
peer address. The key also strips the port, so one client shares one bucket.

internal/worker/ratelimit.go

@@ -2,6 +2,7 @@
 package worker
 
 import (
+	"net"
 	"net/http"
 	"sync"
 	"time"
@@ -206,14 +207,13 @@ func (pcrl *PerClientRateLimiter) Stats() map[string]any {
 }
 
 // PerClientRateLimitMiddleware creates middleware that applies per-client rate limiting.
-// Uses X-Forwarded-For or RemoteAddr to identify clients.
+// Identifies clients by the peer IP of the connection; forwarding headers are spoofable and ignored.
 func PerClientRateLimitMiddleware(limiter *PerClientRateLimiter) func(http.Handler) http.Handler {
 	return func(next http.Handler) http.Handler {
 		return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
-			// Get client identifier (prefer X-Real-IP from RealIP middleware)
 			clientKey := r.RemoteAddr
-			if xff := r.Header.Get("X-Real-IP"); xff != "" {
-				clientKey = xff
+			if host, _, err := net.SplitHostPort(clientKey); err == nil {
+				clientKey = host
 			}
 
 			if !limiter.Allow(clientKey) {

internal/worker/ratelimit_test.go

@@ -0,0 +1,35 @@
+package worker
+
+import (
+	"net/http"
+	"net/http/httptest"
+	"testing"
+)
+
+func TestPerClientRateLimitMiddleware_KeysOnPeerIP(t *testing.T) {
+	h := PerClientRateLimitMiddleware(NewPerClientRateLimiter(0.001, 1))(
+		http.HandlerFunc(func(w http.ResponseWriter, _ *http.Request) { w.WriteHeader(http.StatusOK) }))
+
+	do := func(remote, realIP string) int {
+		req := httptest.NewRequest(http.MethodGet, "/", nil)
+		req.RemoteAddr = remote
+		if realIP != "" {
+			req.Header.Set("X-Real-IP", realIP)
+		}
+		rec := httptest.NewRecorder()
+		h.ServeHTTP(rec, req)
+		return rec.Code
+	}
+
+	if got := do("10.0.0.1:1111", "1.1.1.1"); got != http.StatusOK {
+		t.Fatalf("first request: got %d", got)
+	}
+	// Same peer, new port and forged header: must share the exhausted bucket.
+	if got := do("10.0.0.1:2222", "2.2.2.2"); got != http.StatusTooManyRequests {
+		t.Fatalf("spoofed header/new port bypassed limit: got %d", got)
+	}
+	// Different peer is unaffected.
+	if got := do("10.0.0.2:1111", ""); got != http.StatusOK {
+		t.Fatalf("other peer: got %d", got)
+	}
+}

internal/worker/service.go

@@ -1226,7 +1226,7 @@ func (s *Service) setupMiddleware() {
 	// Add gzip compression for responses >1KB (reduces bandwidth ~70% for JSON)
 	s.router.Use(middleware.Compress(5)) // Level 5 = good balance of speed vs compression
 
-	// Apply per-client rate limiting (after RealIP so we get the real client IP)
+	// Apply per-client rate limiting (keyed on the socket peer address; forwarding headers are untrusted)
 	if s.rateLimiter != nil {
 		s.router.Use(PerClientRateLimitMiddleware(s.rateLimiter))
 	}