[client] categorize root/system-mutating tests behind a privileged build tag

Tests that need root or mutate host state (nftables/iptables/DNS, TUN/WireGuard
interfaces, routes, eBPF, SSH/service install) are now gated behind a
//go:build privileged tag. The default `go test ./client/...` runs as a non-root
user with no sudo and leaves host networking untouched; mixed files were split so
pure-logic tests stay in the default suite.

A self-hosting ory/dockertest/v4 harness (client/testutil/privileged) runs the
privileged suite inside a --privileged --cap-add=NET_ADMIN container via
`make test-privileged`; a DOCKER_CI=true guard skips the spawn when already inside
the container. Added `make test-unit` for the host-safe run.

client/testutil/privileged/runner_test.go

@@ -0,0 +1,155 @@
+//go:build privileged && linux
+
+// Package privileged provides a self-hosting harness that runs the repo's
+// privileged-tagged test suite inside a --privileged --cap-add=NET_ADMIN
+// container, so developers can exercise the root/system-mutating tests on a
+// non-root host with a single `go test` invocation.
+package privileged
+
+import (
+	"bytes"
+	"context"
+	"fmt"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"strings"
+	"testing"
+	"time"
+
+	"github.com/moby/moby/api/types/container"
+	"github.com/ory/dockertest/v4"
+)
+
+// containerImage / containerTag match the image used by the CI privileged job
+// (.github/workflows/golang-test-linux.yml, test_client_on_docker).
+const (
+	containerImage = "golang"
+	containerTag   = "1.25-alpine"
+)
+
+const (
+	containerWorkdir   = "/app"
+	containerGoCache   = "/root/.cache/go-build"
+	containerGoModache = "/go/pkg/mod"
+)
+
+// alpinePackages are the build/runtime deps the privileged tests need, mirroring
+// the CI container setup.
+const alpinePackages = "ca-certificates iptables ip6tables dbus dbus-dev libpcap-dev build-base"
+
+// privilegedTestPackages is the package list the suite runs, excluding the
+// server-side trees and UI/upload helpers, matching the CI Docker job's filter.
+const privilegedTestPackages = `go list -buildvcs=false ./... | grep -v -e /management -e /signal -e /relay -e /proxy -e /combined -e /client/ui -e /upload-server`
+
+// testWriter forwards container output to the test log line by line.
+type testWriter struct{ t *testing.T }
+
+func (w testWriter) Write(p []byte) (int, error) {
+	for _, line := range strings.Split(strings.TrimRight(string(p), "\n"), "\n") {
+		w.t.Log(line)
+	}
+	return len(p), nil
+}
+
+// TestRunPrivilegedSuiteInDocker spins up a privileged container, mounts the repo,
+// and runs `go test -tags 'devcert privileged'` inside it. When already running
+// inside that container (DOCKER_CI=true) it returns immediately so the real
+// privileged tests in the suite execute in place instead of recursing.
+func TestRunPrivilegedSuiteInDocker(t *testing.T) {
+	if os.Getenv("DOCKER_CI") == "true" {
+		t.Skip("inside privileged container, skipping container spawn; privileged tests run in place")
+	}
+
+	repoRoot, err := findRepoRoot()
+	if err != nil {
+		t.Fatalf("locate repo root: %v", err)
+	}
+	goCache, goModCache := hostGoCaches(t)
+
+	// NewPoolT registers container cleanup via t.Cleanup automatically.
+	pool := dockertest.NewPoolT(t, "", dockertest.WithMaxWait(30*time.Minute))
+
+	// Keep the container alive so the suite runs via Exec, which yields a clean
+	// exit code (the v4 Resource API exposes no container wait/exit-code).
+	resource := pool.RunT(t, containerImage,
+		dockertest.WithTag(containerTag),
+		dockertest.WithWorkingDir(containerWorkdir),
+		dockertest.WithMounts([]string{
+			repoRoot + ":" + containerWorkdir,
+			goCache + ":" + containerGoCache,
+			goModCache + ":" + containerGoModache,
+		}),
+		dockertest.WithEnv([]string{
+			"CGO_ENABLED=1",
+			"CI=true",
+			"DOCKER_CI=true",
+			"CONTAINER=true",
+			"GOCACHE=" + containerGoCache,
+			"GOMODCACHE=" + containerGoModache,
+		}),
+		dockertest.WithCmd([]string{"sleep", "infinity"}),
+		dockertest.WithHostConfig(func(hc *container.HostConfig) {
+			hc.Privileged = true
+			hc.CapAdd = []string{"NET_ADMIN"}
+		}),
+		dockertest.WithoutReuse(),
+	)
+
+	ctx, cancel := context.WithTimeout(context.Background(), 30*time.Minute)
+	defer cancel()
+
+	script := fmt.Sprintf(
+		"apk update >/dev/null && apk add --no-cache %s >/dev/null && %s | xargs go test -buildvcs=false -tags 'devcert privileged' -v -timeout 20m -p 1",
+		alpinePackages, privilegedTestPackages,
+	)
+
+	result, err := resource.Exec(ctx, []string{"sh", "-c", script})
+	if err != nil {
+		t.Fatalf("run privileged suite in container: %v", err)
+	}
+
+	w := testWriter{t}
+	_, _ = w.Write([]byte(result.StdOut))
+	_, _ = w.Write([]byte(result.StdErr))
+
+	if result.ExitCode != 0 {
+		t.Fatalf("privileged test suite failed in container (exit code %d)", result.ExitCode)
+	}
+}
+
+// findRepoRoot walks up from the test's working directory to the module root.
+func findRepoRoot() (string, error) {
+	dir, err := os.Getwd()
+	if err != nil {
+		return "", err
+	}
+	for {
+		if _, statErr := os.Stat(filepath.Join(dir, "go.mod")); statErr == nil {
+			return dir, nil
+		}
+		parent := filepath.Dir(dir)
+		if parent == dir {
+			return "", fmt.Errorf("go.mod not found above %s", dir)
+		}
+		dir = parent
+	}
+}
+
+// hostGoCaches resolves the host GOCACHE/GOMODCACHE so the container reuses the
+// existing build/module cache for speed.
+func hostGoCaches(t *testing.T) (string, string) {
+	t.Helper()
+	return goEnv(t, "GOCACHE"), goEnv(t, "GOMODCACHE")
+}
+
+func goEnv(t *testing.T, key string) string {
+	t.Helper()
+	var out bytes.Buffer
+	cmd := exec.Command("go", "env", key)
+	cmd.Stdout = &out
+	if err := cmd.Run(); err != nil {
+		t.Fatalf("go env %s: %v", key, err)
+	}
+	return strings.TrimSpace(out.String())
+}