Add test that shows parsing issue

It's meant to show the pipelining issue. I guess we'll solve the
newly-discovered parsing issue first.

src/connection.hpp

@@ -128,7 +128,7 @@ struct Connection : MessageSender {
    * ```
    */
   void append_message(std::span<std::string_view> data_parts, Arena arena,
-                      bool close_after_send = false) override;
+                      bool close_after_send) override;
 
   /**
    * @brief Get a WeakRef to this connection for async operations.

src/http_handler.cpp

@@ -426,7 +426,7 @@ void HttpHandler::handle_get_metrics(Connection &conn,
   for (auto sv : metrics_span) {
     *out++ = sv;
   }
-  conn.append_message(result, std::move(state.arena));
+  conn.append_message(result, std::move(state.arena), state.connection_close);
   state.reset();
 }
 

tests/test_http_handler.cpp

@@ -4,8 +4,107 @@
 #include "server.hpp"
 
 #include <doctest/doctest.h>
+#include <fcntl.h>
+#include <poll.h>
 #include <string>
 #include <thread>
+#include <unistd.h>
+
+TEST_CASE("HTTP pipelined responses out of order") {
+  weaseldb::Config config;
+  HttpHandler handler(config);
+  auto server = Server::create(config, handler, {});
+  int fd = server->create_local_connection();
+
+  auto runThread = std::thread{[&]() { server->run(); }};
+
+  // Send /ok and /metrics in one write call
+  std::string pipelined_requests = "GET /ok HTTP/1.1\r\n"
+                                   "Host: localhost\r\n"
+                                   "Connection: keep-alive\r\n"
+                                   "\r\n"
+                                   "GET /metrics HTTP/1.1\r\n"
+                                   "Host: localhost\r\n"
+                                   "Connection: keep-alive\r\n"
+                                   "\r\n";
+
+  int w = write(fd, pipelined_requests.c_str(), pipelined_requests.size());
+  REQUIRE(w == static_cast<int>(pipelined_requests.size()));
+
+  // Set socket to non-blocking
+  int flags = fcntl(fd, F_GETFL, 0);
+  fcntl(fd, F_SETFL, flags | O_NONBLOCK);
+
+  // Read all responses with non-blocking I/O and poll
+  char buf[8192];
+  int total_read = 0;
+
+  bool found_ok = false;
+  bool found_http_response = false;
+
+  std::string ok_response_header = "Content-Length: 2";
+
+  while (true) {
+    // Use poll to wait for data availability
+    struct pollfd pfd = {fd, POLLIN, 0};
+    int poll_result = poll(&pfd, 1, -1); // Block indefinitely
+
+    if (poll_result > 0 && (pfd.revents & POLLIN)) {
+      int r = read(fd, buf + total_read, sizeof(buf) - total_read - 1);
+      if (r > 0) {
+        printf("%.*s", r, buf + total_read);
+        total_read += r;
+
+        // Check if we have what we need after each read
+        buf[total_read] = '\0';
+        std::string current_data(buf, total_read);
+
+        found_http_response =
+            current_data.find("HTTP/1.1") != std::string::npos;
+        found_ok = current_data.find(ok_response_header) != std::string::npos;
+
+        // If we have both HTTP response and ok_response_header, we can proceed
+        // with the test
+        if (found_http_response && found_ok) {
+          break;
+        }
+      } else if (r == 0) {
+        REQUIRE(false);
+        break; // EOF
+      } else if (errno != EAGAIN && errno != EWOULDBLOCK) {
+        REQUIRE(false);
+      }
+    }
+  }
+
+  buf[total_read] = '\0';
+  std::string response_data(buf, total_read);
+
+  // Ensure we found both HTTP response and ok_response_header
+  REQUIRE(found_http_response);
+  REQUIRE(found_ok);
+
+  // Find first occurrence of ok_response_header in response body
+  std::size_t ok_pos = response_data.find(ok_response_header);
+  REQUIRE(ok_pos != std::string::npos);
+
+  // Count HTTP response status lines before the ok_response_header
+  std::string before_ok = response_data.substr(0, ok_pos);
+  int http_response_count = 0;
+  std::size_t pos = 0;
+  while ((pos = before_ok.find("HTTP/1.1", pos)) != std::string::npos) {
+    http_response_count++;
+    pos += 8;
+  }
+
+  // Assert there's exactly one HTTP response line before ok_response_header
+  // This would fail if /metrics response comes before /ok response
+  CHECK(http_response_count == 1);
+
+  close(fd);
+  server->shutdown();
+  runThread.join();
+}
 
 TEST_CASE("HTTP pipelined POST requests race condition") {
   weaseldb::Config config;