test(listener): cover ListenerQUIC::Port()

ShouldReportListenerPortQUIC: a listener on port 0 reports a nonzero
port and a client reaches it there; a second listener on port 0 gets a
different port; a fixed port reads back as itself; the port is still
there after Stop() and moves with the listener. It binds no fixed port of
its own: the fixed-port check reuses the ephemeral port a listener just
let go of.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/ShouldReportListenerPortQUIC/main.cpp

@@ -0,0 +1,107 @@
+//SPDX-License-Identifier: LGPL-3.0-only
+//SPDX-FileCopyrightText: Copyright (C) 2026 Catcrafts®
+
+// ListenerQUIC::Port() says which UDP port the listener is bound to, so port
+// 0 (let msquic pick a free one) is usable. Before, nothing read it back: a
+// server had to pick a fixed port and hope nothing else held it, and this
+// suite hands every QUIC test a port of its own by hand.
+//
+// Also: two listeners on port 0 get different ports, a fixed port reads back
+// as itself, and the port is still there after Stop() and gone from a
+// moved-from listener.
+
+#include <cstdio>
+
+import Crafter.Network;
+import Crafter.Thread;
+import std;
+using namespace Crafter;
+
+namespace {
+
+int failures = 0;
+
+void Check(bool ok, std::string_view what) {
+    std::println("{}  {}", ok ? "PASS" : "FAIL", what);
+    if (!ok) ++failures;
+}
+
+std::string Text(const std::vector<char>& bytes) {
+    return std::string(bytes.begin(), bytes.end());
+}
+
+} // namespace
+
+int main() {
+    ThreadPool::Start();
+
+    // A connect that never completes would otherwise sit out the handshake
+    // timeout and the runner's 60 s; fail well before that instead.
+    std::thread([] {
+        std::this_thread::sleep_for(std::chrono::seconds(30));
+        std::println("FAIL  timed out");
+        std::fflush(stdout);
+        std::_Exit(1);
+    }).detach();
+
+    const std::string alpn = "crafter/test-listener-port";
+    QUICServerCredentials serverCreds;
+    serverCreds.selfSigned = true;
+    QUICClientCredentials clientCreds;
+    clientCreds.insecureNoServerValidation = true;
+
+    try {
+        // ── Port 0: msquic picks, Port() says what it picked ─────────────────
+        ListenerQUIC listener(0, alpn, serverCreds, [](ClientQUIC* peer) {
+            peer->OnStream([](QUICStream stream) {
+                try {
+                    std::vector<char> got = stream.RecieveUntilCloseSync();
+                    stream.SendSync(got.data(), static_cast<std::uint32_t>(got.size()), true);
+                } catch (...) {}
+            });
+        });
+        listener.ListenAsyncAsync();
+        const std::uint16_t port = listener.Port();
+        Check(port != 0, std::format("a listener on port 0 reports the port it got ({})", port));
+
+        {
+            ClientQUIC client("localhost", port, alpn, clientCreds);
+            QUICStream stream = client.OpenStream();
+            stream.SendSync("ping", 4, true);
+            const std::string echoed = Text(stream.RecieveUntilCloseSync());
+            Check(echoed == "ping", std::format("a client reaches it at that port ({})", echoed));
+        }
+
+        // ── Another listener on port 0 gets another port ─────────────────────
+        std::uint16_t freed = 0;
+        {
+            ListenerQUIC other(0, alpn, serverCreds, [](ClientQUIC* peer) { delete peer; });
+            freed = other.Port();
+            Check(freed != 0 && freed != port,
+                  std::format("a second listener on port 0 gets a port of its own ({} and {})", port, freed));
+
+            ListenerQUIC moved(std::move(other));
+            Check(moved.Port() == freed && other.Port() == 0,
+                  "moving a listener moves its port; the moved-from one reports 0");
+        }
+
+        // ── A fixed port reads back as itself ────────────────────────────────
+        // The port the listener above let go of: free again, and not one any
+        // other test in the suite binds.
+        {
+            ListenerQUIC fixed(freed, alpn, serverCreds, [](ClientQUIC* peer) { delete peer; });
+            Check(fixed.Port() == freed, std::format("a listener on a fixed port reports that port ({})", fixed.Port()));
+        }
+
+        listener.Stop();
+        Check(listener.Port() == port, "Port() still answers after Stop()");
+    } catch (const std::exception& e) {
+        Check(false, std::format("threw: {}", e.what()));
+    }
+
+    std::println("{}", failures == 0 ? "all checks passed" : "check(s) failed");
+    // As the other QUIC tests: skip the static teardown, which waits for the
+    // accepted peer's idle timeout. _Exit doesn't flush.
+    std::fflush(stdout);
+    std::_Exit(failures == 0 ? 0 : 1);
+}