Add server Timeout middleware for context-based request deadlines

Wraps http.TimeoutHandler to return 503 when handlers exceed the
configured duration. Unlike http.Server.WriteTimeout, this allows
handlers to complete gracefully via context cancellation.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

server/middleware_timeout.go

@@ -0,0 +1,15 @@
+package server
+
+import (
+	"net/http"
+	"time"
+)
+
+// Timeout returns a middleware that limits request processing time.
+// If the handler does not complete within d, the client receives a
+// 503 Service Unavailable response. It wraps http.TimeoutHandler.
+func Timeout(d time.Duration) Middleware {
+	return func(next http.Handler) http.Handler {
+		return http.TimeoutHandler(next, d, "Service Unavailable\n")
+	}
+}

server/middleware_timeout_test.go

@@ -0,0 +1,49 @@
+package server_test
+
+import (
+	"net/http"
+	"net/http/httptest"
+	"testing"
+	"time"
+
+	"git.codelab.vc/pkg/httpx/server"
+)
+
+func TestTimeout(t *testing.T) {
+	t.Run("handler completes within timeout", func(t *testing.T) {
+		handler := server.Timeout(1 * time.Second)(
+			http.HandlerFunc(func(w http.ResponseWriter, _ *http.Request) {
+				w.WriteHeader(http.StatusOK)
+				w.Write([]byte("ok"))
+			}),
+		)
+
+		w := httptest.NewRecorder()
+		req := httptest.NewRequest(http.MethodGet, "/", nil)
+		handler.ServeHTTP(w, req)
+
+		if w.Code != http.StatusOK {
+			t.Fatalf("got status %d, want %d", w.Code, http.StatusOK)
+		}
+	})
+
+	t.Run("handler exceeds timeout returns 503", func(t *testing.T) {
+		handler := server.Timeout(10 * time.Millisecond)(
+			http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+				select {
+				case <-time.After(1 * time.Second):
+				case <-r.Context().Done():
+				}
+				w.WriteHeader(http.StatusOK)
+			}),
+		)
+
+		w := httptest.NewRecorder()
+		req := httptest.NewRequest(http.MethodGet, "/", nil)
+		handler.ServeHTTP(w, req)
+
+		if w.Code != http.StatusServiceUnavailable {
+			t.Fatalf("got status %d, want %d", w.Code, http.StatusServiceUnavailable)
+		}
+	})
+}