feat: skip log collector on hot path when admin API is disabled

changes/unreleased/Changed-20260725-000001.yaml

@@ -0,0 +1,5 @@
+kind: Changed
+body: Skip request log collection on the AWS request hot path when the admin API is disabled (the default). The log collector is now built only when `admin.enabled` is true, avoiding a per-request mutex lock and ring-buffer write that no consumer could read.
+time: 2026-07-25T00:00:01.000000+09:00
+custom:
+    Issue: "112"

cmd/devcloud/main.go

@@ -104,9 +104,13 @@ func main() {
 	// opted in via admin.enabled. Otherwise expose a 404 handler so the admin
 	// routes don't leak service internals. This binary serves no web UI; the
 	// dashboard frontend lives in a separate repository and talks to this API.
-	logCollector := admin.NewLogCollector(1000)
+	// The log collector is only built when admin is enabled; otherwise no
+	// consumer can ever read it, so a nil collector keeps Add off the request
+	// hot path (see gateway.New).
+	var logCollector *admin.LogCollector
 	adminHandler := http.NotFoundHandler()
 	if cfg.Admin.Enabled {
+		logCollector = admin.NewLogCollector(1000)
 		adminAPI := admin.NewAPI(registry, logCollector)
 		hub := admin.NewHub(eventbus.New())
 		go hub.Start()

internal/gateway/gateway.go

@@ -26,27 +26,33 @@ type Gateway struct {
 //   - Requests starting with /devcloud/api/ → adminAPI handler
 //   - Everything else → service router (AWS API)
 //
-// A logging middleware wraps the service router and records each request to
-// logCollector after the response has been written.
+// When logCollector is non-nil, a logging middleware wraps the service router
+// and records each request after the response has been written. A nil
+// collector (admin API disabled) skips that wrapper entirely, keeping the
+// mutex lock + ring-buffer write off the request hot path.
 func New(port int, registry *plugin.Registry, adminAPI http.Handler, logCollector *admin.LogCollector) *Gateway {
 	router := NewServiceRouter(registry)
 
-	// Logging middleware: records AWS API requests to logCollector.
-	loggedRouter := http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
-		start := time.Now()
-		rec := newStatusRecorder(w)
-		router.ServeHTTP(rec, r)
-		logCollector.Add(admin.RequestLog{
-			Method:    r.Method,
-			Path:      r.URL.Path,
-			Status:    rec.statusCode,
-			Duration:  time.Since(start).String(),
-			Timestamp: start,
-			Service:   detectService(r.URL.Path),
+	// Logging middleware: records AWS API requests to logCollector. Only
+	// installed when there is a collector to read them.
+	var serviceHandler http.Handler = router
+	if logCollector != nil {
+		serviceHandler = http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+			start := time.Now()
+			rec := newStatusRecorder(w)
+			router.ServeHTTP(rec, r)
+			logCollector.Add(admin.RequestLog{
+				Method:    r.Method,
+				Path:      r.URL.Path,
+				Status:    rec.statusCode,
+				Duration:  time.Since(start).String(),
+				Timestamp: start,
+				Service:   detectService(r.URL.Path),
+			})
 		})
-	})
+	}
 
-	awsHandler := ChainMiddleware(loggedRouter,
+	awsHandler := ChainMiddleware(serviceHandler,
 		ErrorRecoveryMiddleware,
 		BodyLimitMiddleware,
 		CORSMiddleware,

internal/gateway/gateway_test.go

@@ -46,6 +46,26 @@ func TestGateway_Integration(t *testing.T) {
 	assert.Equal(t, "*", res.Header.Get("Access-Control-Allow-Origin"), "CORS middleware must set Access-Control-Allow-Origin")
 }
 
+func TestGateway_NilLogCollector(t *testing.T) {
+	resp := &plugin.Response{
+		StatusCode:  http.StatusOK,
+		Headers:     map[string]string{},
+		Body:        []byte("<ListBucketResult/>"),
+		ContentType: "application/xml",
+	}
+	reg := newRegistryWithStub("s3", resp)
+
+	// admin disabled → nil collector: the request must succeed without the
+	// logging middleware (no panic, no Add).
+	gw := New(0, reg, http.NotFoundHandler(), nil)
+
+	rec := httptest.NewRecorder()
+	req := httptest.NewRequest(http.MethodGet, "/", nil)
+	gw.server.Handler.ServeHTTP(rec, req)
+
+	assert.Equal(t, http.StatusOK, rec.Code)
+}
+
 func TestGateway_StartShutdown(t *testing.T) {
 	reg := plugin.NewRegistry()
 	lc := admin.NewLogCollector(100)