V2.0.1: listen override fix, sing-box core fetch, probe settings page + fast report, spx removal, core mem env

- 0: sing-box gen overrides fragment listen/port from the inbound row
  (empty listen -> "::"), Update/Add recompute the stored fragment;
  non-loopback E2E against the real core binary.
- 1: agent fetches the sing-box core from the Gitea release when
  missing, self-checks it, and only then latches the switch.
- 2: node list shows the sing-box core version (heartbeat field,
  persisted on the node row), xray version as fallback.
- 3: public-page fallback returns 404 to anonymous visitors when the
  page is disabled.
- 4: settings restart hint bar removed, dead i18n keys cleaned.
- 5: two PUT calls missing JSON headers fixed (audit: only those two),
  batch probe-task creation endpoint + UI.
- 6: cf-probe retirement card and coverage pipeline removed.
- 7: generated vless links no longer carry spx (panel export + sub);
  parser still accepts spx; golden fixtures updated.
- probe batch: dedicated probe settings tab (public-page settings,
  tasks, per-node meta), retention_days editable, per-node traffic
  calibration + stat-interface pinning, runtime metrics split into a
  lightweight fast report (default 3s, 1-60s adjustable).
- 8: sing-box core processes start with GOMEMLIMIT=32MiB, GOGC=50.
- 9: dead /getTwoFactorEnable docs entries removed (frontend call and
  contract entry already gone at base; verified by grep).

internal/agent/singbox_fetch_test.go

@@ -0,0 +1,130 @@
+package agent
+
+import (
+	"net/http"
+	"net/http/httptest"
+	"os"
+	"path/filepath"
+	"strings"
+	"sync/atomic"
+	"testing"
+
+	"github.com/mhsanaei/3x-ui/v3/internal/config"
+)
+
+// V2.0.1 ①: a node missing its sing-box core fetches the pinned
+// release build, self-checks it, and only then reports ready. A
+// failed fetch installs nothing and backs off instead of hammering
+// the release host on every config poll.
+
+// fakeFetchedCore mimics the self-built release binary: it runs,
+// and its `version` carries no stamp ("unknown") — the shape that
+// makes telemetry fall back to the install-time version record.
+const fakeFetchedCore = "#!/bin/sh\necho 'sing-box version unknown'\n"
+
+func fakeCoreServer(t *testing.T, hits *atomic.Int32, status int) *httptest.Server {
+	t.Helper()
+	asset, err := singboxCoreAssetName()
+	if err != nil {
+		t.Skipf("no core asset for this arch: %v", err)
+	}
+	return httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		hits.Add(1)
+		if status != http.StatusOK {
+			w.WriteHeader(status)
+			return
+		}
+		if strings.HasSuffix(r.URL.Path, asset) {
+			_, _ = w.Write([]byte(fakeFetchedCore))
+			return
+		}
+		http.NotFound(w, r)
+	}))
+}
+
+func useCoreBase(t *testing.T, url string) {
+	t.Helper()
+	orig := singboxCoreBaseURL
+	singboxCoreBaseURL = url
+	t.Cleanup(func() { singboxCoreBaseURL = orig })
+}
+
+func TestFetchSingboxCoreInstallsAndSelfChecks(t *testing.T) {
+	binDir := t.TempDir()
+	t.Setenv("XUI_BIN_FOLDER", binDir)
+	var hits atomic.Int32
+	srv := fakeCoreServer(t, &hits, http.StatusOK)
+	defer srv.Close()
+	useCoreBase(t, srv.URL)
+
+	a := &Agent{httpClient: http.DefaultClient}
+	if !a.singboxCoreReady() {
+		t.Fatal("core not ready after fetch")
+	}
+	dest := filepath.Join(binDir, singboxBinaryName())
+	info, err := os.Stat(dest)
+	if err != nil {
+		t.Fatalf("core not installed: %v", err)
+	}
+	if info.Mode()&0o111 == 0 {
+		t.Errorf("installed core is not executable: %v", info.Mode())
+	}
+	if got, ok := a.cachedSingboxVersion(); !ok || got != singboxCoreVersion {
+		t.Errorf("reported core version = %q (ok %v), want %q (from the version record)", got, ok, singboxCoreVersion)
+	}
+	if config.GetBinFolderPath() != binDir {
+		t.Fatalf("bin folder override not in effect")
+	}
+	// Second call: binary present, no further download.
+	if !a.singboxCoreReady() || hits.Load() != 1 {
+		t.Errorf("ready check re-downloaded: hits = %d", hits.Load())
+	}
+}
+
+func TestFetchSingboxCoreFailureKeepsNothingAndBacksOff(t *testing.T) {
+	binDir := t.TempDir()
+	t.Setenv("XUI_BIN_FOLDER", binDir)
+	var hits atomic.Int32
+	srv := fakeCoreServer(t, &hits, http.StatusBadGateway)
+	defer srv.Close()
+	useCoreBase(t, srv.URL)
+
+	a := &Agent{httpClient: http.DefaultClient}
+	if a.singboxCoreReady() {
+		t.Fatal("core reported ready after a failed fetch")
+	}
+	if _, err := os.Stat(filepath.Join(binDir, singboxBinaryName())); !os.IsNotExist(err) {
+		t.Errorf("failed fetch left a core binary behind: %v", err)
+	}
+	// Backoff: an immediate retry must not hit the server again.
+	if err := a.fetchSingboxCoreThrottled(); err == nil {
+		t.Fatal("throttled retry returned no error")
+	}
+	if hits.Load() != 1 {
+		t.Errorf("backoff violated: server hits = %d, want 1", hits.Load())
+	}
+	// And the switch gate stays closed: ready remains false.
+	if a.singboxCoreReady() {
+		t.Error("core became ready during backoff")
+	}
+}
+
+func TestFetchSingboxCoreRejectsBrokenDownload(t *testing.T) {
+	binDir := t.TempDir()
+	t.Setenv("XUI_BIN_FOLDER", binDir)
+	var hits atomic.Int32
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		hits.Add(1)
+		_, _ = w.Write([]byte("this is not a binary at all"))
+	}))
+	defer srv.Close()
+	useCoreBase(t, srv.URL)
+
+	a := &Agent{httpClient: http.DefaultClient}
+	if err := a.fetchSingboxCore(); err == nil {
+		t.Fatal("broken download passed the self-check")
+	}
+	if _, err := os.Stat(filepath.Join(binDir, singboxBinaryName())); !os.IsNotExist(err) {
+		t.Errorf("broken download was installed: %v", err)
+	}
+}