chore: ignore tun2socks source directory in gitignore

- Add daemon CLI subcommand (install/uninstall/status/run)
- Download tun2socks for darwin platforms in Makefile
- Export ExtractTun2Socks and add darwin embed support
- Use group-based pf filtering instead of user-based for transparent
proxying
- Install sudoers rule for passwordless sandbox-exec with _greywall
group
- Add nolint directives for gosec false positives on sudoers 0440 perms
- Fix lint issues: lowercase errors, fmt.Fprintf, nolint comments

.gitignore

@@ -32,3 +32,6 @@ mem.out
 # Embedded binaries (downloaded at build time)
 internal/sandbox/bin/tun2socks-*
 
+# tun2socks source/build directory
+/tun2socks/
+

Makefile

@@ -8,24 +8,24 @@ BINARY_UNIX=$(BINARY_NAME)_unix
 TUN2SOCKS_VERSION=v2.5.2
 TUN2SOCKS_BIN_DIR=internal/sandbox/bin
 
-.PHONY: all build build-ci build-linux test test-ci clean deps install-lint-tools setup setup-ci run fmt lint release release-minor download-tun2socks help
+.PHONY: all build build-ci build-linux build-darwin test test-ci clean deps install-lint-tools setup setup-ci run fmt lint release release-minor download-tun2socks help
 
 all: build
 
+TUN2SOCKS_PLATFORMS=linux-amd64 linux-arm64 darwin-amd64 darwin-arm64
+
 download-tun2socks:
-	@echo "Downloading tun2socks $(TUN2SOCKS_VERSION)..."
 	@mkdir -p $(TUN2SOCKS_BIN_DIR)
-	@curl -sL "https://github.com/xjasonlyu/tun2socks/releases/download/$(TUN2SOCKS_VERSION)/tun2socks-linux-amd64.zip" -o /tmp/tun2socks-linux-amd64.zip
+	@for platform in $(TUN2SOCKS_PLATFORMS); do \
-	@unzip -o -q /tmp/tun2socks-linux-amd64.zip -d /tmp/tun2socks-amd64
+		if [ ! -f $(TUN2SOCKS_BIN_DIR)/tun2socks-$$platform ]; then \
-	@mv /tmp/tun2socks-amd64/tun2socks-linux-amd64 $(TUN2SOCKS_BIN_DIR)/tun2socks-linux-amd64
+			echo "Downloading tun2socks-$$platform $(TUN2SOCKS_VERSION)..."; \
-	@chmod +x $(TUN2SOCKS_BIN_DIR)/tun2socks-linux-amd64
+			curl -sL "https://github.com/xjasonlyu/tun2socks/releases/download/$(TUN2SOCKS_VERSION)/tun2socks-$$platform.zip" -o /tmp/tun2socks-$$platform.zip; \
-	@rm -rf /tmp/tun2socks-linux-amd64.zip /tmp/tun2socks-amd64
+			unzip -o -q /tmp/tun2socks-$$platform.zip -d /tmp/tun2socks-$$platform; \
-	@curl -sL "https://github.com/xjasonlyu/tun2socks/releases/download/$(TUN2SOCKS_VERSION)/tun2socks-linux-arm64.zip" -o /tmp/tun2socks-linux-arm64.zip
+			mv /tmp/tun2socks-$$platform/tun2socks-$$platform $(TUN2SOCKS_BIN_DIR)/tun2socks-$$platform; \
-	@unzip -o -q /tmp/tun2socks-linux-arm64.zip -d /tmp/tun2socks-arm64
+			chmod +x $(TUN2SOCKS_BIN_DIR)/tun2socks-$$platform; \
-	@mv /tmp/tun2socks-arm64/tun2socks-linux-arm64 $(TUN2SOCKS_BIN_DIR)/tun2socks-linux-arm64
+			rm -rf /tmp/tun2socks-$$platform.zip /tmp/tun2socks-$$platform; \
-	@chmod +x $(TUN2SOCKS_BIN_DIR)/tun2socks-linux-arm64
+		fi; \
-	@rm -rf /tmp/tun2socks-linux-arm64.zip /tmp/tun2socks-arm64
+	done
-	@echo "tun2socks binaries downloaded to $(TUN2SOCKS_BIN_DIR)/"
 
 build: download-tun2socks
 	@echo "Building $(BINARY_NAME)..."
@@ -53,6 +53,7 @@ clean:
 	rm -f $(BINARY_UNIX)
 	rm -f coverage.out
 	rm -f $(TUN2SOCKS_BIN_DIR)/tun2socks-linux-*
+	rm -f $(TUN2SOCKS_BIN_DIR)/tun2socks-darwin-*
 
 deps:
 	@echo "Downloading dependencies..."
@@ -63,7 +64,7 @@ build-linux: download-tun2socks
 	@echo "Building for Linux..."
 	CGO_ENABLED=0 GOOS=linux GOARCH=amd64 $(GOBUILD) -o $(BINARY_UNIX) -v ./cmd/greywall
 
-build-darwin:
+build-darwin: download-tun2socks
 	@echo "Building for macOS..."
 	CGO_ENABLED=0 GOOS=darwin GOARCH=arm64 $(GOBUILD) -o $(BINARY_NAME)_darwin -v ./cmd/greywall
 

cmd/greywall/daemon.go

@@ -0,0 +1,229 @@
+package main
+
+import (
+	"bufio"
+	"fmt"
+	"os"
+	"os/signal"
+	"path/filepath"
+	"runtime"
+	"strings"
+	"syscall"
+
+	"github.com/spf13/cobra"
+
+	"gitea.app.monadical.io/monadical/greywall/internal/daemon"
+	"gitea.app.monadical.io/monadical/greywall/internal/sandbox"
+)
+
+// newDaemonCmd creates the daemon subcommand tree:
+//
+//	greywall daemon
+//	  install     - Install the LaunchDaemon (requires root)
+//	  uninstall   - Uninstall the LaunchDaemon (requires root)
+//	  run         - Run the daemon (called by LaunchDaemon plist)
+//	  status      - Show daemon status
+func newDaemonCmd() *cobra.Command {
+	cmd := &cobra.Command{
+		Use:   "daemon",
+		Short: "Manage the greywall background daemon",
+		Long: `Manage the greywall LaunchDaemon for transparent network sandboxing on macOS.
+
+The daemon runs as a system service and manages the tun2socks tunnel, DNS relay,
+and pf rules that enable transparent proxy routing for sandboxed processes.
+
+Commands:
+  sudo greywall daemon install     Install and start the daemon
+  sudo greywall daemon uninstall   Stop and remove the daemon
+  greywall daemon status           Check daemon status
+  greywall daemon run              Run the daemon (used by LaunchDaemon)`,
+	}
+
+	cmd.AddCommand(
+		newDaemonInstallCmd(),
+		newDaemonUninstallCmd(),
+		newDaemonRunCmd(),
+		newDaemonStatusCmd(),
+	)
+
+	return cmd
+}
+
+// newDaemonInstallCmd creates the "daemon install" subcommand.
+func newDaemonInstallCmd() *cobra.Command {
+	return &cobra.Command{
+		Use:   "install",
+		Short: "Install the greywall LaunchDaemon (requires root)",
+		Long: `Install greywall as a macOS LaunchDaemon. This command:
+  1. Creates a system user (_greywall) for sandboxed process isolation
+  2. Copies the greywall binary to /usr/local/bin/greywall
+  3. Extracts and installs the tun2socks binary
+  4. Installs a LaunchDaemon plist for automatic startup
+  5. Loads and starts the daemon
+
+Requires root privileges: sudo greywall daemon install`,
+		RunE: func(cmd *cobra.Command, args []string) error {
+			exePath, err := os.Executable()
+			if err != nil {
+				return fmt.Errorf("failed to determine executable path: %w", err)
+			}
+			exePath, err = filepath.EvalSymlinks(exePath)
+			if err != nil {
+				return fmt.Errorf("failed to resolve executable path: %w", err)
+			}
+
+			// Extract embedded tun2socks binary to a temp file.
+			tun2socksPath, err := sandbox.ExtractTun2Socks()
+			if err != nil {
+				return fmt.Errorf("failed to extract tun2socks: %w", err)
+			}
+			defer os.Remove(tun2socksPath) //nolint:errcheck // temp file cleanup
+
+			if err := daemon.Install(exePath, tun2socksPath, debug); err != nil {
+				return err
+			}
+
+			fmt.Println()
+			fmt.Println("To check status:   greywall daemon status")
+			fmt.Println("To uninstall:      sudo greywall daemon uninstall")
+			return nil
+		},
+	}
+}
+
+// newDaemonUninstallCmd creates the "daemon uninstall" subcommand.
+func newDaemonUninstallCmd() *cobra.Command {
+	var force bool
+
+	cmd := &cobra.Command{
+		Use:   "uninstall",
+		Short: "Uninstall the greywall LaunchDaemon (requires root)",
+		Long: `Uninstall the greywall LaunchDaemon. This command:
+  1. Stops and unloads the daemon
+  2. Removes the LaunchDaemon plist
+  3. Removes installed files
+  4. Removes the _greywall system user and group
+
+Requires root privileges: sudo greywall daemon uninstall`,
+		RunE: func(cmd *cobra.Command, args []string) error {
+			if !force {
+				fmt.Println("The following will be removed:")
+				fmt.Printf("  - LaunchDaemon plist:  %s\n", daemon.LaunchDaemonPlistPath)
+				fmt.Printf("  - Binary:              %s\n", daemon.InstallBinaryPath)
+				fmt.Printf("  - Lib directory:       %s\n", daemon.InstallLibDir)
+				fmt.Printf("  - Socket:              %s\n", daemon.DefaultSocketPath)
+				fmt.Printf("  - Sudoers file:        %s\n", daemon.SudoersFilePath)
+				fmt.Printf("  - System user/group:   %s\n", daemon.SandboxUserName)
+				fmt.Println()
+				fmt.Print("Proceed with uninstall? [y/N] ")
+
+				reader := bufio.NewReader(os.Stdin)
+				answer, _ := reader.ReadString('\n')
+				answer = strings.TrimSpace(strings.ToLower(answer))
+				if answer != "y" && answer != "yes" {
+					fmt.Println("Uninstall cancelled.")
+					return nil
+				}
+			}
+
+			if err := daemon.Uninstall(debug); err != nil {
+				return err
+			}
+
+			fmt.Println()
+			fmt.Println("The greywall daemon has been uninstalled.")
+			return nil
+		},
+	}
+
+	cmd.Flags().BoolVarP(&force, "force", "f", false, "Skip confirmation prompt")
+	return cmd
+}
+
+// newDaemonRunCmd creates the "daemon run" subcommand. This is invoked by
+// the LaunchDaemon plist and should not normally be called manually.
+func newDaemonRunCmd() *cobra.Command {
+	return &cobra.Command{
+		Use:    "run",
+		Short:  "Run the daemon process (called by LaunchDaemon)",
+		Hidden: true, // Not intended for direct user invocation.
+		RunE:   runDaemon,
+	}
+}
+
+// newDaemonStatusCmd creates the "daemon status" subcommand.
+func newDaemonStatusCmd() *cobra.Command {
+	return &cobra.Command{
+		Use:   "status",
+		Short: "Show the daemon status",
+		Long:  `Check whether the greywall daemon is installed and running. Does not require root.`,
+		RunE: func(cmd *cobra.Command, args []string) error {
+			installed := daemon.IsInstalled()
+			running := daemon.IsRunning()
+
+			fmt.Printf("Greywall daemon status:\n")
+			fmt.Printf("  Installed: %s\n", boolStatus(installed))
+			fmt.Printf("  Running:   %s\n", boolStatus(running))
+			fmt.Printf("  Plist:     %s\n", daemon.LaunchDaemonPlistPath)
+			fmt.Printf("  Binary:    %s\n", daemon.InstallBinaryPath)
+			fmt.Printf("  User:      %s\n", daemon.SandboxUserName)
+			fmt.Printf("  Group:     %s (pf routing)\n", daemon.SandboxGroupName)
+			fmt.Printf("  Sudoers:   %s\n", daemon.SudoersFilePath)
+			fmt.Printf("  Socket:    %s\n", daemon.DefaultSocketPath)
+
+			if !installed {
+				fmt.Println()
+				fmt.Println("The daemon is not installed. Run: sudo greywall daemon install")
+			} else if !running {
+				fmt.Println()
+				fmt.Println("The daemon is installed but not running.")
+				fmt.Printf("Check logs: cat /var/log/greywall.log\n")
+				fmt.Printf("Start it:   sudo launchctl load %s\n", daemon.LaunchDaemonPlistPath)
+			}
+
+			return nil
+		},
+	}
+}
+
+// runDaemon is the main entry point for the daemon process. It starts the
+// Unix socket server and blocks until a termination signal is received.
+// CLI clients connect to the server to request sessions (which create
+// utun tunnels, DNS relays, and pf rules on demand).
+func runDaemon(cmd *cobra.Command, args []string) error {
+	tun2socksPath := filepath.Join(daemon.InstallLibDir, "tun2socks-darwin-"+runtime.GOARCH)
+	if _, err := os.Stat(tun2socksPath); err != nil {
+		return fmt.Errorf("tun2socks binary not found at %s (run 'sudo greywall daemon install' first)", tun2socksPath)
+	}
+
+	daemon.Logf("Starting daemon (tun2socks=%s, socket=%s)", tun2socksPath, daemon.DefaultSocketPath)
+
+	srv := daemon.NewServer(daemon.DefaultSocketPath, tun2socksPath, debug)
+	if err := srv.Start(); err != nil {
+		return fmt.Errorf("failed to start daemon server: %w", err)
+	}
+
+	daemon.Logf("Daemon started, listening on %s", daemon.DefaultSocketPath)
+
+	// Wait for termination signal.
+	sigCh := make(chan os.Signal, 1)
+	signal.Notify(sigCh, syscall.SIGINT, syscall.SIGTERM)
+	sig := <-sigCh
+	daemon.Logf("Received signal %s, shutting down", sig)
+
+	if err := srv.Stop(); err != nil {
+		daemon.Logf("Shutdown error: %v", err)
+		return err
+	}
+
+	daemon.Logf("Daemon stopped")
+	return nil
+}
+
+// boolStatus returns a human-readable string for a boolean status value.
+func boolStatus(b bool) string {
+	if b {
+		return "yes"
+	}
+	return "no"
+}

cmd/greywall/main.go

@@ -111,6 +111,7 @@ Configuration file format:
 
 	rootCmd.AddCommand(newCompletionCmd(rootCmd))
 	rootCmd.AddCommand(newTemplatesCmd())
+	rootCmd.AddCommand(newDaemonCmd())
 
 	if err := rootCmd.Execute(); err != nil {
 		fmt.Fprintf(os.Stderr, "Error: %v\n", err)
@@ -594,12 +595,12 @@ parseCommand:
 	// Find the executable
 	execPath, err := exec.LookPath(command[0])
 	if err != nil {
-		fmt.Fprintf(os.Stderr, "[greywall:landlock-wrapper] Error: command not found: %s\n", command[0])
+		fmt.Fprintf(os.Stderr, "[greywall:landlock-wrapper] Error: command not found: %s\n", command[0]) //nolint:gosec // logging to stderr, not web output
 		os.Exit(127)
 	}
 
 	if debugMode {
-		fmt.Fprintf(os.Stderr, "[greywall:landlock-wrapper] Exec: %s %v\n", execPath, command[1:])
+		fmt.Fprintf(os.Stderr, "[greywall:landlock-wrapper] Exec: %s %v\n", execPath, command[1:]) //nolint:gosec // logging to stderr, not web output
 	}
 
 	// Sanitize environment (strips LD_PRELOAD, etc.)

internal/daemon/client.go

@@ -0,0 +1,144 @@
+package daemon
+
+import (
+	"encoding/json"
+	"fmt"
+	"net"
+	"os"
+	"time"
+)
+
+const (
+	// clientDialTimeout is the maximum time to wait when connecting to the daemon.
+	clientDialTimeout = 5 * time.Second
+
+	// clientReadTimeout is the maximum time to wait for a response from the daemon.
+	clientReadTimeout = 30 * time.Second
+)
+
+// Client communicates with the greywall daemon over a Unix socket using
+// newline-delimited JSON.
+type Client struct {
+	socketPath string
+	debug      bool
+}
+
+// NewClient creates a new daemon client that connects to the given Unix socket path.
+func NewClient(socketPath string, debug bool) *Client {
+	return &Client{
+		socketPath: socketPath,
+		debug:      debug,
+	}
+}
+
+// CreateSession asks the daemon to create a new sandbox session with the given
+// proxy URL and optional DNS address. Returns the session info on success.
+func (c *Client) CreateSession(proxyURL, dnsAddr string) (*Response, error) {
+	req := Request{
+		Action:   "create_session",
+		ProxyURL: proxyURL,
+		DNSAddr:  dnsAddr,
+	}
+
+	resp, err := c.sendRequest(req)
+	if err != nil {
+		return nil, fmt.Errorf("create session request failed: %w", err)
+	}
+
+	if !resp.OK {
+		return resp, fmt.Errorf("create session failed: %s", resp.Error)
+	}
+
+	return resp, nil
+}
+
+// DestroySession asks the daemon to tear down the session with the given ID.
+func (c *Client) DestroySession(sessionID string) error {
+	req := Request{
+		Action:    "destroy_session",
+		SessionID: sessionID,
+	}
+
+	resp, err := c.sendRequest(req)
+	if err != nil {
+		return fmt.Errorf("destroy session request failed: %w", err)
+	}
+
+	if !resp.OK {
+		return fmt.Errorf("destroy session failed: %s", resp.Error)
+	}
+
+	return nil
+}
+
+// Status queries the daemon for its current status.
+func (c *Client) Status() (*Response, error) {
+	req := Request{
+		Action: "status",
+	}
+
+	resp, err := c.sendRequest(req)
+	if err != nil {
+		return nil, fmt.Errorf("status request failed: %w", err)
+	}
+
+	if !resp.OK {
+		return resp, fmt.Errorf("status request failed: %s", resp.Error)
+	}
+
+	return resp, nil
+}
+
+// IsRunning checks whether the daemon is reachable by attempting to connect
+// to the Unix socket. Returns true if the connection succeeds.
+func (c *Client) IsRunning() bool {
+	conn, err := net.DialTimeout("unix", c.socketPath, clientDialTimeout)
+	if err != nil {
+		return false
+	}
+	_ = conn.Close()
+	return true
+}
+
+// sendRequest connects to the daemon Unix socket, sends a JSON-encoded request,
+// and reads back a JSON-encoded response.
+func (c *Client) sendRequest(req Request) (*Response, error) {
+	c.logDebug("Connecting to daemon at %s", c.socketPath)
+
+	conn, err := net.DialTimeout("unix", c.socketPath, clientDialTimeout)
+	if err != nil {
+		return nil, fmt.Errorf("failed to connect to daemon at %s: %w", c.socketPath, err)
+	}
+	defer conn.Close() //nolint:errcheck // best-effort close on request completion
+
+	// Set a read deadline for the response.
+	if err := conn.SetReadDeadline(time.Now().Add(clientReadTimeout)); err != nil {
+		return nil, fmt.Errorf("failed to set read deadline: %w", err)
+	}
+
+	// Send the request as newline-delimited JSON.
+	encoder := json.NewEncoder(conn)
+	if err := encoder.Encode(req); err != nil {
+		return nil, fmt.Errorf("failed to send request: %w", err)
+	}
+
+	c.logDebug("Sent request: action=%s", req.Action)
+
+	// Read the response.
+	decoder := json.NewDecoder(conn)
+	var resp Response
+	if err := decoder.Decode(&resp); err != nil {
+		return nil, fmt.Errorf("failed to read response: %w", err)
+	}
+
+	c.logDebug("Received response: ok=%v", resp.OK)
+
+	return &resp, nil
+}
+
+// logDebug writes a debug message to stderr with the [greywall:daemon] prefix.
+func (c *Client) logDebug(format string, args ...interface{}) {
+	if c.debug {
+		fmt.Fprintf(os.Stderr, "[greywall:daemon] "+format+"\n", args...)
+	}
+}

internal/daemon/dns.go

@@ -0,0 +1,186 @@
+//go:build darwin || linux
+
+package daemon
+
+import (
+	"fmt"
+	"net"
+	"os"
+	"sync"
+	"time"
+)
+
+const (
+	// maxDNSPacketSize is the maximum UDP packet size we accept.
+	// DNS can theoretically be up to 65535 bytes, but practically much smaller.
+	maxDNSPacketSize = 4096
+
+	// upstreamTimeout is the time we wait for a response from the upstream DNS server.
+	upstreamTimeout = 5 * time.Second
+)
+
+// DNSRelay is a UDP DNS relay that forwards DNS queries from sandboxed processes
+// to a configured upstream DNS server. It operates as a simple packet relay without
+// parsing DNS protocol contents.
+type DNSRelay struct {
+	udpConn    *net.UDPConn
+	targetAddr string // upstream DNS server address (host:port)
+	listenAddr string // address we're listening on
+	wg         sync.WaitGroup
+	done       chan struct{}
+	debug      bool
+}
+
+// NewDNSRelay creates a new DNS relay that listens on listenAddr and forwards
+// queries to dnsAddr. The listenAddr will typically be "127.0.0.2:53" (loopback alias).
+// The dnsAddr must be in "host:port" format (e.g. "1.1.1.1:53").
+func NewDNSRelay(listenAddr, dnsAddr string, debug bool) (*DNSRelay, error) {
+	// Validate the upstream DNS address is parseable as host:port.
+	targetHost, targetPort, err := net.SplitHostPort(dnsAddr)
+	if err != nil {
+		return nil, fmt.Errorf("invalid DNS address %q: %w", dnsAddr, err)
+	}
+	if targetHost == "" {
+		return nil, fmt.Errorf("invalid DNS address %q: empty host", dnsAddr)
+	}
+	if targetPort == "" {
+		return nil, fmt.Errorf("invalid DNS address %q: empty port", dnsAddr)
+	}
+
+	// Resolve and bind the listen address.
+	udpAddr, err := net.ResolveUDPAddr("udp", listenAddr)
+	if err != nil {
+		return nil, fmt.Errorf("failed to resolve listen address %q: %w", listenAddr, err)
+	}
+
+	conn, err := net.ListenUDP("udp", udpAddr)
+	if err != nil {
+		return nil, fmt.Errorf("failed to bind UDP socket on %q: %w", listenAddr, err)
+	}
+
+	return &DNSRelay{
+		udpConn:    conn,
+		targetAddr: dnsAddr,
+		listenAddr: conn.LocalAddr().String(),
+		done:       make(chan struct{}),
+		debug:      debug,
+	}, nil
+}
+
+// ListenAddr returns the actual address the relay is listening on.
+// This is useful when port 0 was used to get an ephemeral port.
+func (d *DNSRelay) ListenAddr() string {
+	return d.listenAddr
+}
+
+// Start begins the DNS relay loop. It reads incoming UDP packets from the
+// listening socket and spawns a goroutine per query to forward it to the
+// upstream DNS server and relay the response back.
+func (d *DNSRelay) Start() error {
+	if d.debug {
+		fmt.Fprintf(os.Stderr, "[greywall:dns-relay] Listening on %s, forwarding to %s\n", d.listenAddr, d.targetAddr)
+	}
+
+	d.wg.Add(1)
+	go d.readLoop()
+
+	return nil
+}
+
+// Stop shuts down the DNS relay. It signals the read loop to stop, closes the
+// listening socket, and waits for all in-flight queries to complete.
+func (d *DNSRelay) Stop() {
+	close(d.done)
+	_ = d.udpConn.Close()
+	d.wg.Wait()
+
+	if d.debug {
+		fmt.Fprintf(os.Stderr, "[greywall:dns-relay] Stopped\n")
+	}
+}
+
+// readLoop is the main loop that reads incoming DNS queries from the listening socket.
+func (d *DNSRelay) readLoop() {
+	defer d.wg.Done()
+
+	buf := make([]byte, maxDNSPacketSize)
+	for {
+		n, clientAddr, err := d.udpConn.ReadFromUDP(buf)
+		if err != nil {
+			select {
+			case <-d.done:
+				// Shutting down, expected error from closed socket.
+				return
+			default:
+				fmt.Fprintf(os.Stderr, "[greywall:dns-relay] Read error: %v\n", err)
+				continue
+			}
+		}
+
+		if n == 0 {
+			continue
+		}
+
+		// Copy the packet data so the buffer can be reused immediately.
+		query := make([]byte, n)
+		copy(query, buf[:n])
+
+		d.wg.Add(1)
+		go d.handleQuery(query, clientAddr)
+	}
+}
+
+// handleQuery forwards a single DNS query to the upstream server and relays
+// the response back to the original client. It creates a dedicated UDP connection
+// to the upstream server to avoid multiplexing complexity.
+func (d *DNSRelay) handleQuery(query []byte, clientAddr *net.UDPAddr) {
+	defer d.wg.Done()
+
+	if d.debug {
+		fmt.Fprintf(os.Stderr, "[greywall:dns-relay] Query from %s (%d bytes)\n", clientAddr, len(query))
+	}
+
+	// Create a dedicated UDP connection to the upstream DNS server.
+	upstreamConn, err := net.Dial("udp", d.targetAddr)
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "[greywall:dns-relay] Failed to connect to upstream %s: %v\n", d.targetAddr, err)
+		return
+	}
+	defer upstreamConn.Close() //nolint:errcheck // best-effort cleanup of per-query UDP connection
+
+	// Send the query to the upstream server.
+	if _, err := upstreamConn.Write(query); err != nil {
+		fmt.Fprintf(os.Stderr, "[greywall:dns-relay] Failed to send query to upstream: %v\n", err)
+		return
+	}
+
+	// Wait for the response with a timeout.
+	if err := upstreamConn.SetReadDeadline(time.Now().Add(upstreamTimeout)); err != nil {
+		fmt.Fprintf(os.Stderr, "[greywall:dns-relay] Failed to set read deadline: %v\n", err)
+		return
+	}
+
+	resp := make([]byte, maxDNSPacketSize)
+	n, err := upstreamConn.Read(resp)
+	if err != nil {
+		if d.debug {
+			fmt.Fprintf(os.Stderr, "[greywall:dns-relay] Upstream response error: %v\n", err)
+		}
+		return
+	}
+
+	// Send the response back to the original client.
+	if _, err := d.udpConn.WriteToUDP(resp[:n], clientAddr); err != nil {
+		// The listening socket may have been closed during shutdown.
+		select {
+		case <-d.done:
+			return
+		default:
+			fmt.Fprintf(os.Stderr, "[greywall:dns-relay] Failed to send response to %s: %v\n", clientAddr, err)
+		}
+	}
+
+	if d.debug {
+		fmt.Fprintf(os.Stderr, "[greywall:dns-relay] Response to %s (%d bytes)\n", clientAddr, n)
+	}
+}

internal/daemon/dns_test.go

@@ -0,0 +1,296 @@
+//go:build darwin || linux
+
+package daemon
+
+import (
+	"bytes"
+	"net"
+	"sync"
+	"testing"
+	"time"
+)
+
+// startMockDNSServer starts a UDP server that echoes back whatever it receives,
+// prefixed with "RESP:" to distinguish responses from queries.
+// Returns the server's address and a cleanup function.
+func startMockDNSServer(t *testing.T) (string, func()) {
+	t.Helper()
+
+	addr, err := net.ResolveUDPAddr("udp", "127.0.0.1:0")
+	if err != nil {
+		t.Fatalf("Failed to resolve address: %v", err)
+	}
+
+	conn, err := net.ListenUDP("udp", addr)
+	if err != nil {
+		t.Fatalf("Failed to start mock DNS server: %v", err)
+	}
+
+	done := make(chan struct{})
+	go func() {
+		buf := make([]byte, maxDNSPacketSize)
+		for {
+			n, remoteAddr, err := conn.ReadFromUDP(buf)
+			if err != nil {
+				select {
+				case <-done:
+					return
+				default:
+					continue
+				}
+			}
+			// Echo back with "RESP:" prefix.
+			resp := append([]byte("RESP:"), buf[:n]...)
+			_, _ = conn.WriteToUDP(resp, remoteAddr) // best-effort in test
+		}
+	}()
+
+	cleanup := func() {
+		close(done)
+		_ = conn.Close()
+	}
+
+	return conn.LocalAddr().String(), cleanup
+}
+
+// startSilentDNSServer starts a UDP server that accepts connections but never
+// responds, simulating an upstream timeout.
+func startSilentDNSServer(t *testing.T) (string, func()) {
+	t.Helper()
+
+	addr, err := net.ResolveUDPAddr("udp", "127.0.0.1:0")
+	if err != nil {
+		t.Fatalf("Failed to resolve address: %v", err)
+	}
+
+	conn, err := net.ListenUDP("udp", addr)
+	if err != nil {
+		t.Fatalf("Failed to start silent DNS server: %v", err)
+	}
+
+	cleanup := func() {
+		_ = conn.Close()
+	}
+
+	return conn.LocalAddr().String(), cleanup
+}
+
+func TestDNSRelay_ForwardPacket(t *testing.T) {
+	// Start a mock upstream DNS server.
+	upstreamAddr, cleanupUpstream := startMockDNSServer(t)
+	defer cleanupUpstream()
+
+	// Create and start the relay.
+	relay, err := NewDNSRelay("127.0.0.1:0", upstreamAddr, true)
+	if err != nil {
+		t.Fatalf("Failed to create DNS relay: %v", err)
+	}
+
+	if err := relay.Start(); err != nil {
+		t.Fatalf("Failed to start DNS relay: %v", err)
+	}
+	defer relay.Stop()
+
+	// Send a query through the relay.
+	clientConn, err := net.Dial("udp", relay.ListenAddr())
+	if err != nil {
+		t.Fatalf("Failed to connect to relay: %v", err)
+	}
+	defer clientConn.Close() //nolint:errcheck // test cleanup
+
+	query := []byte("test-dns-query")
+	if _, err := clientConn.Write(query); err != nil {
+		t.Fatalf("Failed to send query: %v", err)
+	}
+
+	// Read the response.
+	if err := clientConn.SetReadDeadline(time.Now().Add(5 * time.Second)); err != nil {
+		t.Fatalf("Failed to set read deadline: %v", err)
+	}
+
+	buf := make([]byte, maxDNSPacketSize)
+	n, err := clientConn.Read(buf)
+	if err != nil {
+		t.Fatalf("Failed to read response: %v", err)
+	}
+
+	expected := append([]byte("RESP:"), query...)
+	if !bytes.Equal(buf[:n], expected) {
+		t.Errorf("Unexpected response: got %q, want %q", buf[:n], expected)
+	}
+}
+
+func TestDNSRelay_UpstreamTimeout(t *testing.T) {
+	// Start a silent upstream server that never responds.
+	upstreamAddr, cleanupUpstream := startSilentDNSServer(t)
+	defer cleanupUpstream()
+
+	// Create and start the relay.
+	relay, err := NewDNSRelay("127.0.0.1:0", upstreamAddr, false)
+	if err != nil {
+		t.Fatalf("Failed to create DNS relay: %v", err)
+	}
+
+	if err := relay.Start(); err != nil {
+		t.Fatalf("Failed to start DNS relay: %v", err)
+	}
+	defer relay.Stop()
+
+	// Send a query through the relay.
+	clientConn, err := net.Dial("udp", relay.ListenAddr())
+	if err != nil {
+		t.Fatalf("Failed to connect to relay: %v", err)
+	}
+	defer clientConn.Close() //nolint:errcheck // test cleanup
+
+	query := []byte("test-dns-timeout")
+	if _, err := clientConn.Write(query); err != nil {
+		t.Fatalf("Failed to send query: %v", err)
+	}
+
+	// The relay should not send back a response because upstream timed out.
+	// Set a short deadline on the client side; we expect no data.
+	if err := clientConn.SetReadDeadline(time.Now().Add(6 * time.Second)); err != nil {
+		t.Fatalf("Failed to set read deadline: %v", err)
+	}
+
+	buf := make([]byte, maxDNSPacketSize)
+	_, err = clientConn.Read(buf)
+	if err == nil {
+		t.Fatal("Expected timeout error reading from relay, but got a response")
+	}
+
+	// Verify it was a timeout error.
+	netErr, ok := err.(net.Error)
+	if !ok || !netErr.Timeout() {
+		t.Fatalf("Expected timeout error, got: %v", err)
+	}
+}
+
+func TestDNSRelay_ConcurrentQueries(t *testing.T) {
+	// Start a mock upstream DNS server.
+	upstreamAddr, cleanupUpstream := startMockDNSServer(t)
+	defer cleanupUpstream()
+
+	// Create and start the relay.
+	relay, err := NewDNSRelay("127.0.0.1:0", upstreamAddr, false)
+	if err != nil {
+		t.Fatalf("Failed to create DNS relay: %v", err)
+	}
+
+	if err := relay.Start(); err != nil {
+		t.Fatalf("Failed to start DNS relay: %v", err)
+	}
+	defer relay.Stop()
+
+	const numQueries = 20
+	var wg sync.WaitGroup
+	errors := make(chan error, numQueries)
+
+	for i := range numQueries {
+		wg.Add(1)
+		go func(id int) {
+			defer wg.Done()
+
+			clientConn, err := net.Dial("udp", relay.ListenAddr())
+			if err != nil {
+				errors <- err
+				return
+			}
+			defer clientConn.Close() //nolint:errcheck // test cleanup
+
+			query := []byte("concurrent-query-" + string(rune('A'+id))) //nolint:gosec // test uses small range 0-19, no overflow
+			if _, err := clientConn.Write(query); err != nil {
+				errors <- err
+				return
+			}
+
+			if err := clientConn.SetReadDeadline(time.Now().Add(5 * time.Second)); err != nil {
+				errors <- err
+				return
+			}
+
+			buf := make([]byte, maxDNSPacketSize)
+			n, err := clientConn.Read(buf)
+			if err != nil {
+				errors <- err
+				return
+			}
+
+			expected := append([]byte("RESP:"), query...)
+			if !bytes.Equal(buf[:n], expected) {
+				errors <- &unexpectedResponseError{got: buf[:n], want: expected}
+			}
+		}(i)
+	}
+
+	wg.Wait()
+	close(errors)
+
+	for err := range errors {
+		t.Errorf("Concurrent query error: %v", err)
+	}
+}
+
+func TestDNSRelay_ListenAddr(t *testing.T) {
+	// Use port 0 to get an ephemeral port.
+	relay, err := NewDNSRelay("127.0.0.1:0", "1.1.1.1:53", false)
+	if err != nil {
+		t.Fatalf("Failed to create DNS relay: %v", err)
+	}
+	defer relay.Stop()
+
+	addr := relay.ListenAddr()
+	if addr == "" {
+		t.Fatal("ListenAddr returned empty string")
+	}
+
+	host, port, err := net.SplitHostPort(addr)
+	if err != nil {
+		t.Fatalf("ListenAddr returned invalid address %q: %v", addr, err)
+	}
+	if host != "127.0.0.1" {
+		t.Errorf("Expected host 127.0.0.1, got %q", host)
+	}
+	if port == "0" {
+		t.Error("Expected assigned port, got 0")
+	}
+}
+
+func TestNewDNSRelay_InvalidDNSAddr(t *testing.T) {
+	tests := []struct {
+		name    string
+		dnsAddr string
+	}{
+		{"missing port", "1.1.1.1"},
+		{"empty string", ""},
+		{"empty host", ":53"},
+		{"empty port", "1.1.1.1:"},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			_, err := NewDNSRelay("127.0.0.1:0", tt.dnsAddr, false)
+			if err == nil {
+				t.Errorf("Expected error for DNS address %q, got nil", tt.dnsAddr)
+			}
+		})
+	}
+}
+
+func TestNewDNSRelay_InvalidListenAddr(t *testing.T) {
+	_, err := NewDNSRelay("invalid-addr", "1.1.1.1:53", false)
+	if err == nil {
+		t.Error("Expected error for invalid listen address, got nil")
+	}
+}
+
+// unexpectedResponseError is used to report mismatched responses in concurrent tests.
+type unexpectedResponseError struct {
+	got  []byte
+	want []byte
+}
+
+func (e *unexpectedResponseError) Error() string {
+	return "unexpected response: got " + string(e.got) + ", want " + string(e.want)
+}

internal/daemon/launchd.go

@@ -0,0 +1,554 @@
+//go:build darwin
+
+package daemon
+
+import (
+	"fmt"
+	"io"
+	"net"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"runtime"
+	"strconv"
+	"strings"
+	"time"
+)
+
+const (
+	LaunchDaemonLabel     = "co.greyhaven.greywall"
+	LaunchDaemonPlistPath = "/Library/LaunchDaemons/co.greyhaven.greywall.plist"
+	InstallBinaryPath     = "/usr/local/bin/greywall"
+	InstallLibDir         = "/usr/local/lib/greywall"
+	SandboxUserName       = "_greywall"
+	SandboxUserUID        = "399"       // System user range on macOS
+	SandboxGroupName      = "_greywall" // Group used for pf routing (same name as user)
+	SudoersFilePath       = "/etc/sudoers.d/greywall"
+	DefaultSocketPath     = "/var/run/greywall.sock"
+)
+
+// Install performs the full LaunchDaemon installation flow:
+//  1. Verify running as root
+//  2. Create system user _greywall
+//  3. Create /usr/local/lib/greywall/ directory and copy tun2socks
+//  4. Copy the current binary to /usr/local/bin/greywall
+//  5. Generate and write the LaunchDaemon plist
+//  6. Set proper permissions, load the daemon, and verify it starts
+func Install(currentBinaryPath, tun2socksPath string, debug bool) error {
+	if os.Getuid() != 0 {
+		return fmt.Errorf("daemon install must be run as root (use sudo)")
+	}
+
+	// Step 1: Create system user and group.
+	if err := createSandboxUser(debug); err != nil {
+		return fmt.Errorf("failed to create sandbox user: %w", err)
+	}
+
+	// Step 1b: Install sudoers rule for group-based sandbox-exec.
+	if err := installSudoersRule(debug); err != nil {
+		return fmt.Errorf("failed to install sudoers rule: %w", err)
+	}
+
+	// Step 1c: Add invoking user to _greywall group.
+	addInvokingUserToGroup(debug)
+
+	// Step 2: Create lib directory and copy tun2socks.
+	logDebug(debug, "Creating directory %s", InstallLibDir)
+	if err := os.MkdirAll(InstallLibDir, 0o755); err != nil { //nolint:gosec // system lib directory needs 0755 for daemon access
+		return fmt.Errorf("failed to create %s: %w", InstallLibDir, err)
+	}
+	tun2socksDst := filepath.Join(InstallLibDir, "tun2socks-darwin-"+runtime.GOARCH)
+	logDebug(debug, "Copying tun2socks to %s", tun2socksDst)
+	if err := copyFile(tun2socksPath, tun2socksDst, 0o755); err != nil {
+		return fmt.Errorf("failed to install tun2socks: %w", err)
+	}
+
+	// Step 3: Copy binary to install path.
+	if err := os.MkdirAll(filepath.Dir(InstallBinaryPath), 0o755); err != nil { //nolint:gosec // /usr/local/bin needs 0755
+		return fmt.Errorf("failed to create %s: %w", filepath.Dir(InstallBinaryPath), err)
+	}
+	logDebug(debug, "Copying binary from %s to %s", currentBinaryPath, InstallBinaryPath)
+	if err := copyFile(currentBinaryPath, InstallBinaryPath, 0o755); err != nil {
+		return fmt.Errorf("failed to install binary: %w", err)
+	}
+
+	// Step 4: Generate and write plist.
+	plist := generatePlist()
+	logDebug(debug, "Writing plist to %s", LaunchDaemonPlistPath)
+	if err := os.WriteFile(LaunchDaemonPlistPath, []byte(plist), 0o644); err != nil { //nolint:gosec // LaunchDaemon plist requires 0644 per macOS convention
+		return fmt.Errorf("failed to write plist: %w", err)
+	}
+
+	// Step 5: Set ownership to root:wheel.
+	logDebug(debug, "Setting ownership on %s to root:wheel", LaunchDaemonPlistPath)
+	if err := runCmd(debug, "chown", "root:wheel", LaunchDaemonPlistPath); err != nil {
+		return fmt.Errorf("failed to set plist ownership: %w", err)
+	}
+
+	// Step 6: Load the daemon.
+	logDebug(debug, "Loading LaunchDaemon")
+	if err := runCmd(debug, "launchctl", "load", LaunchDaemonPlistPath); err != nil {
+		return fmt.Errorf("failed to load daemon: %w", err)
+	}
+
+	// Step 7: Verify the daemon actually started.
+	running := false
+	for range 10 {
+		time.Sleep(500 * time.Millisecond)
+		if IsRunning() {
+			running = true
+			break
+		}
+	}
+
+	Logf("Daemon installed successfully.")
+	Logf("  Plist:     %s", LaunchDaemonPlistPath)
+	Logf("  Binary:    %s", InstallBinaryPath)
+	Logf("  Tun2socks: %s", tun2socksDst)
+	actualUID := readDsclAttr(SandboxUserName, "UniqueID", true)
+	actualGID := readDsclAttr(SandboxGroupName, "PrimaryGroupID", false)
+	Logf("  User:      %s (UID %s)", SandboxUserName, actualUID)
+	Logf("  Group:     %s (GID %s, pf routing)", SandboxGroupName, actualGID)
+	Logf("  Sudoers:   %s", SudoersFilePath)
+	Logf("  Log:       /var/log/greywall.log")
+
+	if !running {
+		Logf("  Status:    NOT RUNNING (check /var/log/greywall.log)")
+		return fmt.Errorf("daemon was loaded but failed to start; check /var/log/greywall.log")
+	}
+
+	Logf("  Status:    running")
+	return nil
+}
+
+// Uninstall performs the full LaunchDaemon uninstallation flow. It attempts
+// every cleanup step even if individual steps fail, collecting errors along
+// the way.
+func Uninstall(debug bool) error {
+	if os.Getuid() != 0 {
+		return fmt.Errorf("daemon uninstall must be run as root (use sudo)")
+	}
+
+	var errs []string
+
+	// Step 1: Unload daemon (best effort).
+	logDebug(debug, "Unloading LaunchDaemon")
+	if err := runCmd(debug, "launchctl", "unload", LaunchDaemonPlistPath); err != nil {
+		errs = append(errs, fmt.Sprintf("unload daemon: %v", err))
+	}
+
+	// Step 2: Remove plist file.
+	logDebug(debug, "Removing plist %s", LaunchDaemonPlistPath)
+	if err := os.Remove(LaunchDaemonPlistPath); err != nil && !os.IsNotExist(err) {
+		errs = append(errs, fmt.Sprintf("remove plist: %v", err))
+	}
+
+	// Step 3: Remove lib directory.
+	logDebug(debug, "Removing directory %s", InstallLibDir)
+	if err := os.RemoveAll(InstallLibDir); err != nil {
+		errs = append(errs, fmt.Sprintf("remove lib dir: %v", err))
+	}
+
+	// Step 4: Remove installed binary, but only if it differs from the
+	// currently running executable.
+	currentExe, exeErr := os.Executable()
+	if exeErr != nil {
+		currentExe = ""
+	}
+	resolvedCurrent, _ := filepath.EvalSymlinks(currentExe)
+	resolvedInstall, _ := filepath.EvalSymlinks(InstallBinaryPath)
+	if resolvedCurrent != resolvedInstall {
+		logDebug(debug, "Removing binary %s", InstallBinaryPath)
+		if err := os.Remove(InstallBinaryPath); err != nil && !os.IsNotExist(err) {
+			errs = append(errs, fmt.Sprintf("remove binary: %v", err))
+		}
+	} else {
+		logDebug(debug, "Skipping binary removal (currently running from %s)", InstallBinaryPath)
+	}
+
+	// Step 5: Remove system user and group.
+	if err := removeSandboxUser(debug); err != nil {
+		errs = append(errs, fmt.Sprintf("remove sandbox user: %v", err))
+	}
+
+	// Step 6: Remove socket file if it exists.
+	logDebug(debug, "Removing socket %s", DefaultSocketPath)
+	if err := os.Remove(DefaultSocketPath); err != nil && !os.IsNotExist(err) {
+		errs = append(errs, fmt.Sprintf("remove socket: %v", err))
+	}
+
+	// Step 6b: Remove sudoers file.
+	logDebug(debug, "Removing sudoers file %s", SudoersFilePath)
+	if err := os.Remove(SudoersFilePath); err != nil && !os.IsNotExist(err) {
+		errs = append(errs, fmt.Sprintf("remove sudoers file: %v", err))
+	}
+
+	// Step 7: Remove pf anchor lines from /etc/pf.conf.
+	if err := removeAnchorFromPFConf(debug); err != nil {
+		errs = append(errs, fmt.Sprintf("remove pf anchor: %v", err))
+	}
+
+	if len(errs) > 0 {
+		Logf("Uninstall completed with warnings:")
+		for _, e := range errs {
+			Logf("  - %s", e)
+		}
+		return nil // partial cleanup is not a fatal error
+	}
+
+	Logf("Daemon uninstalled successfully.")
+	return nil
+}
+
+// generatePlist returns the LaunchDaemon plist XML content.
+func generatePlist() string {
+	return `<?xml version="1.0" encoding="UTF-8"?>
+<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN"
+  "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
+<plist version="1.0">
+<dict>
+  <key>Label</key>
+  <string>` + LaunchDaemonLabel + `</string>
+  <key>ProgramArguments</key>
+  <array>
+    <string>` + InstallBinaryPath + `</string>
+    <string>daemon</string>
+    <string>run</string>
+  </array>
+  <key>RunAtLoad</key><true/>
+  <key>KeepAlive</key><true/>
+  <key>StandardOutPath</key>
+  <string>/var/log/greywall.log</string>
+  <key>StandardErrorPath</key>
+  <string>/var/log/greywall.log</string>
+</dict>
+</plist>
+`
+}
+
+// IsInstalled returns true if the LaunchDaemon plist file exists.
+func IsInstalled() bool {
+	_, err := os.Stat(LaunchDaemonPlistPath)
+	return err == nil
+}
+
+// IsRunning returns true if the daemon is currently running. It first tries
+// connecting to the Unix socket (works without root), then falls back to
+// launchctl print which can inspect the system domain without root.
+func IsRunning() bool {
+	// Primary check: try to connect to the daemon socket. This proves the
+	// daemon is actually running and accepting connections.
+	conn, err := net.DialTimeout("unix", DefaultSocketPath, 2*time.Second)
+	if err == nil {
+		_ = conn.Close()
+		return true
+	}
+
+	// Fallback: launchctl print system/<label> works without root on modern
+	// macOS (unlike launchctl list which only shows the caller's domain).
+	//nolint:gosec // LaunchDaemonLabel is a constant
+	out, err := exec.Command("launchctl", "print", "system/"+LaunchDaemonLabel).CombinedOutput()
+	if err != nil {
+		return false
+	}
+	return strings.Contains(string(out), "state = running")
+}
+
+// createSandboxUser creates the _greywall system user and group on macOS
+// using dscl (Directory Service command line utility).
+//
+// If the user/group already exist with valid IDs, they are reused. Otherwise
+// a free UID/GID is found dynamically (the hardcoded SandboxUserUID is only
+// a preferred default — macOS system groups like com.apple.access_ssh may
+// already claim it).
+func createSandboxUser(debug bool) error {
+	userPath := "/Users/" + SandboxUserName
+	groupPath := "/Groups/" + SandboxUserName
+
+	// Check if user already exists with a valid UniqueID.
+	existingUID := readDsclAttr(SandboxUserName, "UniqueID", true)
+	existingGID := readDsclAttr(SandboxGroupName, "PrimaryGroupID", false)
+
+	if existingUID != "" && existingGID != "" {
+		logDebug(debug, "System user %s (UID %s) and group (GID %s) already exist",
+			SandboxUserName, existingUID, existingGID)
+		return nil
+	}
+
+	// Find a free ID. Try the preferred default first, then scan.
+	id := SandboxUserUID
+	if !isIDFree(id, debug) {
+		var err error
+		id, err = findFreeSystemID(debug)
+		if err != nil {
+			return fmt.Errorf("failed to find free UID/GID: %w", err)
+		}
+		logDebug(debug, "Preferred ID %s is taken, using %s instead", SandboxUserUID, id)
+	}
+
+	// Create the group record FIRST (so the GID exists before the user references it).
+	logDebug(debug, "Ensuring system group %s (GID %s)", SandboxGroupName, id)
+	if existingGID == "" {
+		groupCmds := [][]string{
+			{"dscl", ".", "-create", groupPath},
+			{"dscl", ".", "-create", groupPath, "PrimaryGroupID", id},
+			{"dscl", ".", "-create", groupPath, "RealName", "Greywall Sandbox"},
+		}
+		for _, args := range groupCmds {
+			if err := runDsclCreate(debug, args); err != nil {
+				return err
+			}
+		}
+		// Verify the GID was actually set (runDsclCreate may have skipped it).
+		actualGID := readDsclAttr(SandboxGroupName, "PrimaryGroupID", false)
+		if actualGID == "" {
+			return fmt.Errorf("failed to set PrimaryGroupID on group %s (GID %s may be taken)", SandboxGroupName, id)
+		}
+	}
+
+	// Create the user record.
+	logDebug(debug, "Ensuring system user %s (UID %s)", SandboxUserName, id)
+	if existingUID == "" {
+		userCmds := [][]string{
+			{"dscl", ".", "-create", userPath},
+			{"dscl", ".", "-create", userPath, "UniqueID", id},
+			{"dscl", ".", "-create", userPath, "PrimaryGroupID", id},
+			{"dscl", ".", "-create", userPath, "UserShell", "/usr/bin/false"},
+			{"dscl", ".", "-create", userPath, "RealName", "Greywall Sandbox"},
+			{"dscl", ".", "-create", userPath, "NFSHomeDirectory", "/var/empty"},
+		}
+		for _, args := range userCmds {
+			if err := runDsclCreate(debug, args); err != nil {
+				return err
+			}
+		}
+	}
+
+	logDebug(debug, "System user and group %s ready (ID %s)", SandboxUserName, id)
+	return nil
+}
+
+// readDsclAttr reads a single attribute from a user or group record.
+// Returns empty string if the record or attribute does not exist.
+func readDsclAttr(name, attr string, isUser bool) string {
+	recordType := "/Groups/"
+	if isUser {
+		recordType = "/Users/"
+	}
+	//nolint:gosec // name and attr are controlled constants
+	out, err := exec.Command("dscl", ".", "-read", recordType+name, attr).Output()
+	if err != nil {
+		return ""
+	}
+	// Output format: "AttrName: value"
+	parts := strings.SplitN(strings.TrimSpace(string(out)), ": ", 2)
+	if len(parts) != 2 {
+		return ""
+	}
+	return strings.TrimSpace(parts[1])
+}
+
+// isIDFree checks whether a given numeric ID is available as both a UID and GID.
+func isIDFree(id string, debug bool) bool {
+	// Check if any user has this UniqueID.
+	//nolint:gosec // id is a controlled numeric string
+	out, err := exec.Command("dscl", ".", "-search", "/Users", "UniqueID", id).Output()
+	if err == nil && strings.TrimSpace(string(out)) != "" {
+		logDebug(debug, "ID %s is taken by a user", id)
+		return false
+	}
+	// Check if any group has this PrimaryGroupID.
+	//nolint:gosec // id is a controlled numeric string
+	out, err = exec.Command("dscl", ".", "-search", "/Groups", "PrimaryGroupID", id).Output()
+	if err == nil && strings.TrimSpace(string(out)) != "" {
+		logDebug(debug, "ID %s is taken by a group", id)
+		return false
+	}
+	return true
+}
+
+// findFreeSystemID scans the macOS system ID range (350–499) for a UID/GID
+// pair that is not in use by any existing user or group.
+func findFreeSystemID(debug bool) (string, error) {
+	for i := 350; i < 500; i++ {
+		id := strconv.Itoa(i)
+		if isIDFree(id, debug) {
+			return id, nil
+		}
+	}
+	return "", fmt.Errorf("no free system UID/GID found in range 350-499")
+}
+
+// runDsclCreate runs a dscl -create command, silently ignoring
+// eDSRecordAlreadyExists errors (idempotent for repeated installs).
+func runDsclCreate(debug bool, args []string) error {
+	err := runCmd(debug, args[0], args[1:]...)
+	if err != nil && strings.Contains(err.Error(), "eDSRecordAlreadyExists") {
+		logDebug(debug, "Already exists, skipping: %s", strings.Join(args, " "))
+		return nil
+	}
+	if err != nil {
+		return fmt.Errorf("dscl command failed (%s): %w", strings.Join(args, " "), err)
+	}
+	return nil
+}
+
+// removeSandboxUser removes the _greywall system user and group.
+func removeSandboxUser(debug bool) error {
+	var errs []string
+
+	userPath := "/Users/" + SandboxUserName
+	groupPath := "/Groups/" + SandboxUserName
+
+	if userExists(SandboxUserName) {
+		logDebug(debug, "Removing system user %s", SandboxUserName)
+		if err := runCmd(debug, "dscl", ".", "-delete", userPath); err != nil {
+			errs = append(errs, fmt.Sprintf("delete user: %v", err))
+		}
+	}
+
+	// Check if group exists before trying to remove.
+	logDebug(debug, "Removing system group %s", SandboxUserName)
+	if err := runCmd(debug, "dscl", ".", "-delete", groupPath); err != nil {
+		// Group may not exist; only record error if it's not a "not found" case.
+		errStr := err.Error()
+		if !strings.Contains(errStr, "not found") && !strings.Contains(errStr, "does not exist") {
+			errs = append(errs, fmt.Sprintf("delete group: %v", err))
+		}
+	}
+
+	if len(errs) > 0 {
+		return fmt.Errorf("sandbox user removal issues: %s", strings.Join(errs, "; "))
+	}
+	return nil
+}
+
+// userExists checks if a user exists on macOS by querying the directory service.
+func userExists(username string) bool {
+	//nolint:gosec // username is a controlled constant
+	err := exec.Command("dscl", ".", "-read", "/Users/"+username).Run()
+	return err == nil
+}
+
+// installSudoersRule writes a sudoers rule that allows members of the
+// _greywall group to run sandbox-exec as any user with group _greywall,
+// without a password. The rule is validated with visudo -cf before install.
+func installSudoersRule(debug bool) error {
+	rule := fmt.Sprintf("%%%s ALL = (ALL:%s) NOPASSWD: /usr/bin/sandbox-exec *\n",
+		SandboxGroupName, SandboxGroupName)
+
+	logDebug(debug, "Writing sudoers rule to %s", SudoersFilePath)
+
+	// Ensure /etc/sudoers.d exists.
+	if err := os.MkdirAll(filepath.Dir(SudoersFilePath), 0o755); err != nil { //nolint:gosec // /etc/sudoers.d must be 0755
+		return fmt.Errorf("failed to create sudoers directory: %w", err)
+	}
+
+	// Write to a temp file first, then validate with visudo.
+	tmpFile := SudoersFilePath + ".tmp"
+	if err := os.WriteFile(tmpFile, []byte(rule), 0o440); err != nil { //nolint:gosec // sudoers files require 0440 per sudo(8)
+		return fmt.Errorf("failed to write sudoers temp file: %w", err)
+	}
+
+	// Validate syntax before installing.
+	//nolint:gosec // tmpFile is a controlled path
+	if err := runCmd(debug, "visudo", "-cf", tmpFile); err != nil {
+		_ = os.Remove(tmpFile)
+		return fmt.Errorf("sudoers validation failed: %w", err)
+	}
+
+	// Move validated file into place.
+	if err := os.Rename(tmpFile, SudoersFilePath); err != nil {
+		_ = os.Remove(tmpFile)
+		return fmt.Errorf("failed to install sudoers file: %w", err)
+	}
+
+	// Ensure correct ownership (root:wheel) and permissions (0440).
+	if err := runCmd(debug, "chown", "root:wheel", SudoersFilePath); err != nil {
+		return fmt.Errorf("failed to set sudoers ownership: %w", err)
+	}
+	if err := os.Chmod(SudoersFilePath, 0o440); err != nil { //nolint:gosec // sudoers files require 0440 per sudo(8)
+		return fmt.Errorf("failed to set sudoers permissions: %w", err)
+	}
+
+	logDebug(debug, "Sudoers rule installed: %s", SudoersFilePath)
+	return nil
+}
+
+// addInvokingUserToGroup adds the real invoking user (detected via SUDO_USER)
+// to the _greywall group so they can use sudo -g _greywall. This is non-fatal;
+// if it fails, a manual instruction is printed.
+//
+// We use dscl -append (not dseditgroup) because dseditgroup can reset group
+// attributes like PrimaryGroupID on freshly created groups.
+func addInvokingUserToGroup(debug bool) {
+	realUser := os.Getenv("SUDO_USER")
+	if realUser == "" || realUser == "root" {
+		Logf("Note: Could not detect invoking user (SUDO_USER not set).")
+		Logf("  You may need to manually add your user to the %s group:", SandboxGroupName)
+		Logf("  sudo dscl . -append /Groups/%s GroupMembership YOUR_USERNAME", SandboxGroupName)
+		return
+	}
+
+	groupPath := "/Groups/" + SandboxGroupName
+	logDebug(debug, "Adding user %s to group %s", realUser, SandboxGroupName)
+	//nolint:gosec // realUser comes from SUDO_USER env var set by sudo
+	err := runCmd(debug, "dscl", ".", "-append", groupPath, "GroupMembership", realUser)
+	if err != nil {
+		Logf("Warning: failed to add %s to group %s: %v", realUser, SandboxGroupName, err)
+		Logf("  You may need to run manually:")
+		Logf("  sudo dscl . -append %s GroupMembership %s", groupPath, realUser)
+	} else {
+		Logf("  User %s added to group %s", realUser, SandboxGroupName)
+	}
+}
+
+// copyFile copies a file from src to dst with the given permissions.
+func copyFile(src, dst string, perm os.FileMode) error {
+	srcFile, err := os.Open(src) //nolint:gosec // src is from os.Executable or user flag
+	if err != nil {
+		return fmt.Errorf("open source %s: %w", src, err)
+	}
+	defer srcFile.Close() //nolint:errcheck // read-only file; close error is not actionable
+
+	dstFile, err := os.OpenFile(dst, os.O_WRONLY|os.O_CREATE|os.O_TRUNC, perm) //nolint:gosec // dst is a controlled install path constant
+	if err != nil {
+		return fmt.Errorf("create destination %s: %w", dst, err)
+	}
+	defer dstFile.Close() //nolint:errcheck // best-effort close; errors from Chmod/Copy are checked
+
+	if _, err := io.Copy(dstFile, srcFile); err != nil {
+		return fmt.Errorf("copy data: %w", err)
+	}
+
+	if err := dstFile.Chmod(perm); err != nil {
+		return fmt.Errorf("set permissions on %s: %w", dst, err)
+	}
+
+	return nil
+}
+
+// runCmd executes a command and returns an error if it fails. When debug is
+// true, the command is logged before execution.
+func runCmd(debug bool, name string, args ...string) error {
+	logDebug(debug, "exec: %s %s", name, strings.Join(args, " "))
+	//nolint:gosec // arguments are constructed from internal constants
+	cmd := exec.Command(name, args...)
+	if output, err := cmd.CombinedOutput(); err != nil {
+		return fmt.Errorf("%s failed: %w (output: %s)", name, err, strings.TrimSpace(string(output)))
+	}
+	return nil
+}
+
+// logDebug writes a timestamped debug message to stderr.
+func logDebug(debug bool, format string, args ...interface{}) {
+	if debug {
+		Logf(format, args...)
+	}
+}
+
+// Logf writes a timestamped message to stderr with the [greywall:daemon] prefix.
+func Logf(format string, args ...interface{}) {
+	ts := time.Now().Format("2006-01-02 15:04:05")
+	fmt.Fprintf(os.Stderr, ts+" [greywall:daemon] "+format+"\n", args...)
+}

internal/daemon/launchd_stub.go

@@ -0,0 +1,37 @@
+//go:build !darwin
+
+package daemon
+
+import "fmt"
+
+const (
+	LaunchDaemonLabel     = "co.greyhaven.greywall"
+	LaunchDaemonPlistPath = "/Library/LaunchDaemons/co.greyhaven.greywall.plist"
+	InstallBinaryPath     = "/usr/local/bin/greywall"
+	InstallLibDir         = "/usr/local/lib/greywall"
+	SandboxUserName       = "_greywall"
+	SandboxUserUID        = "399"
+	SandboxGroupName      = "_greywall"
+	SudoersFilePath       = "/etc/sudoers.d/greywall"
+	DefaultSocketPath     = "/var/run/greywall.sock"
+)
+
+// Install is only supported on macOS.
+func Install(currentBinaryPath, tun2socksPath string, debug bool) error {
+	return fmt.Errorf("daemon install is only supported on macOS")
+}
+
+// Uninstall is only supported on macOS.
+func Uninstall(debug bool) error {
+	return fmt.Errorf("daemon uninstall is only supported on macOS")
+}
+
+// IsInstalled always returns false on non-macOS platforms.
+func IsInstalled() bool {
+	return false
+}
+
+// IsRunning always returns false on non-macOS platforms.
+func IsRunning() bool {
+	return false
+}

internal/daemon/launchd_test.go

@@ -0,0 +1,129 @@
+//go:build darwin
+
+package daemon
+
+import (
+	"strings"
+	"testing"
+)
+
+func TestGeneratePlist(t *testing.T) {
+	plist := generatePlist()
+
+	// Verify it is valid-looking XML with the expected plist header.
+	if !strings.HasPrefix(plist, `<?xml version="1.0" encoding="UTF-8"?>`) {
+		t.Error("plist should start with XML declaration")
+	}
+
+	if !strings.Contains(plist, `<!DOCTYPE plist PUBLIC`) {
+		t.Error("plist should contain DOCTYPE declaration")
+	}
+
+	if !strings.Contains(plist, `<plist version="1.0">`) {
+		t.Error("plist should contain plist version tag")
+	}
+
+	// Verify the label matches the constant.
+	expectedLabel := "<string>" + LaunchDaemonLabel + "</string>"
+	if !strings.Contains(plist, expectedLabel) {
+		t.Errorf("plist should contain label %q", LaunchDaemonLabel)
+	}
+
+	// Verify program arguments.
+	if !strings.Contains(plist, "<string>"+InstallBinaryPath+"</string>") {
+		t.Errorf("plist should reference binary path %q", InstallBinaryPath)
+	}
+
+	if !strings.Contains(plist, "<string>daemon</string>") {
+		t.Error("plist should contain 'daemon' argument")
+	}
+
+	if !strings.Contains(plist, "<string>run</string>") {
+		t.Error("plist should contain 'run' argument")
+	}
+
+	// Verify RunAtLoad and KeepAlive.
+	if !strings.Contains(plist, "<key>RunAtLoad</key><true/>") {
+		t.Error("plist should have RunAtLoad set to true")
+	}
+
+	if !strings.Contains(plist, "<key>KeepAlive</key><true/>") {
+		t.Error("plist should have KeepAlive set to true")
+	}
+
+	// Verify log paths.
+	if !strings.Contains(plist, "/var/log/greywall.log") {
+		t.Error("plist should reference /var/log/greywall.log for stdout/stderr")
+	}
+}
+
+func TestGeneratePlistProgramArguments(t *testing.T) {
+	plist := generatePlist()
+
+	// Verify the ProgramArguments array contains exactly 3 entries in order.
+	// The array should be: /usr/local/bin/greywall, daemon, run
+	argStart := strings.Index(plist, "<key>ProgramArguments</key>")
+	if argStart == -1 {
+		t.Fatal("plist should contain ProgramArguments key")
+	}
+
+	// Extract the array section.
+	arrayStart := strings.Index(plist[argStart:], "<array>")
+	arrayEnd := strings.Index(plist[argStart:], "</array>")
+	if arrayStart == -1 || arrayEnd == -1 {
+		t.Fatal("ProgramArguments should contain an array")
+	}
+
+	arrayContent := plist[argStart+arrayStart : argStart+arrayEnd]
+
+	expectedArgs := []string{InstallBinaryPath, "daemon", "run"}
+	for _, arg := range expectedArgs {
+		if !strings.Contains(arrayContent, "<string>"+arg+"</string>") {
+			t.Errorf("ProgramArguments array should contain %q", arg)
+		}
+	}
+}
+
+func TestIsInstalledReturnsFalse(t *testing.T) {
+	// On a test machine without the daemon installed, this should return false.
+	// We cannot guarantee the daemon is not installed, but on most dev machines
+	// it will not be. This test verifies the function runs without panicking.
+	result := IsInstalled()
+
+	// We only validate the function returns a bool without error.
+	// On CI/dev machines the plist should not exist.
+	_ = result
+}
+
+func TestIsRunningReturnsFalse(t *testing.T) {
+	// On a test machine without the daemon running, this should return false.
+	// Similar to TestIsInstalledReturnsFalse, we verify it runs cleanly.
+	result := IsRunning()
+	_ = result
+}
+
+func TestConstants(t *testing.T) {
+	// Verify constants have expected values.
+	tests := []struct {
+		name     string
+		got      string
+		expected string
+	}{
+		{"LaunchDaemonLabel", LaunchDaemonLabel, "co.greyhaven.greywall"},
+		{"LaunchDaemonPlistPath", LaunchDaemonPlistPath, "/Library/LaunchDaemons/co.greyhaven.greywall.plist"},
+		{"InstallBinaryPath", InstallBinaryPath, "/usr/local/bin/greywall"},
+		{"InstallLibDir", InstallLibDir, "/usr/local/lib/greywall"},
+		{"SandboxUserName", SandboxUserName, "_greywall"},
+		{"SandboxUserUID", SandboxUserUID, "399"},
+		{"SandboxGroupName", SandboxGroupName, "_greywall"},
+		{"SudoersFilePath", SudoersFilePath, "/etc/sudoers.d/greywall"},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if tt.got != tt.expected {
+				t.Errorf("%s = %q, want %q", tt.name, tt.got, tt.expected)
+			}
+		})
+	}
+}

internal/daemon/relay.go

@@ -0,0 +1,246 @@
+//go:build darwin || linux
+
+package daemon
+
+import (
+	"fmt"
+	"io"
+	"net"
+	"net/url"
+	"os"
+	"sync"
+	"sync/atomic"
+	"time"
+)
+
+const (
+	defaultMaxConns    = 256
+	connIdleTimeout    = 5 * time.Minute
+	upstreamDialTimout = 10 * time.Second
+)
+
+// Relay is a pure Go TCP relay that forwards connections from local listeners
+// to an upstream SOCKS5 proxy address. It does NOT implement the SOCKS5 protocol;
+// it blindly forwards bytes between the local connection and the upstream proxy.
+type Relay struct {
+	listeners   []net.Listener // both IPv4 and IPv6 listeners
+	targetAddr  string         // external SOCKS5 proxy host:port
+	port        int            // assigned port
+	wg          sync.WaitGroup
+	done        chan struct{}
+	debug       bool
+	maxConns    int          // max concurrent connections (default 256)
+	activeConns atomic.Int32 // current active connections
+}
+
+// NewRelay parses a proxy URL to extract host:port and binds listeners on both
+// 127.0.0.1 and [::1] using the same port. The port is dynamically assigned
+// from the first (IPv4) bind. If the IPv6 bind fails, the relay continues
+// with IPv4 only. Binding both addresses prevents IPv6 port squatting attacks.
+func NewRelay(proxyURL string, debug bool) (*Relay, error) {
+	u, err := url.Parse(proxyURL)
+	if err != nil {
+		return nil, fmt.Errorf("invalid proxy URL %q: %w", proxyURL, err)
+	}
+
+	host := u.Hostname()
+	port := u.Port()
+	if host == "" || port == "" {
+		return nil, fmt.Errorf("proxy URL must include host and port: %q", proxyURL)
+	}
+	targetAddr := net.JoinHostPort(host, port)
+
+	// Bind IPv4 first to get a dynamically assigned port.
+	ipv4Listener, err := net.Listen("tcp4", "127.0.0.1:0")
+	if err != nil {
+		return nil, fmt.Errorf("failed to bind IPv4 listener: %w", err)
+	}
+
+	assignedPort := ipv4Listener.Addr().(*net.TCPAddr).Port
+	listeners := []net.Listener{ipv4Listener}
+
+	// Bind IPv6 on the same port. If it fails, log and continue with IPv4 only.
+	ipv6Addr := fmt.Sprintf("[::1]:%d", assignedPort)
+	ipv6Listener, err := net.Listen("tcp6", ipv6Addr)
+	if err != nil {
+		if debug {
+			fmt.Fprintf(os.Stderr, "[greywall:relay] IPv6 bind on %s failed, continuing IPv4 only: %v\n", ipv6Addr, err)
+		}
+	} else {
+		listeners = append(listeners, ipv6Listener)
+	}
+
+	if debug {
+		fmt.Fprintf(os.Stderr, "[greywall:relay] Bound %d listener(s) on port %d -> %s\n", len(listeners), assignedPort, targetAddr)
+	}
+
+	return &Relay{
+		listeners:  listeners,
+		targetAddr: targetAddr,
+		port:       assignedPort,
+		done:       make(chan struct{}),
+		debug:      debug,
+		maxConns:   defaultMaxConns,
+	}, nil
+}
+
+// Port returns the local port the relay is listening on.
+func (r *Relay) Port() int {
+	return r.port
+}
+
+// Start begins accepting connections on all listeners. Each accepted connection
+// is handled in its own goroutine with bidirectional forwarding to the upstream
+// proxy address. Start returns immediately; use Stop to shut down.
+func (r *Relay) Start() error {
+	for _, ln := range r.listeners {
+		r.wg.Add(1)
+		go r.acceptLoop(ln)
+	}
+	return nil
+}
+
+// Stop gracefully shuts down the relay by closing all listeners and waiting
+// for in-flight connections to finish.
+func (r *Relay) Stop() {
+	close(r.done)
+	for _, ln := range r.listeners {
+		_ = ln.Close()
+	}
+	r.wg.Wait()
+}
+
+// acceptLoop runs the accept loop for a single listener.
+func (r *Relay) acceptLoop(ln net.Listener) {
+	defer r.wg.Done()
+
+	for {
+		conn, err := ln.Accept()
+		if err != nil {
+			select {
+			case <-r.done:
+				return
+			default:
+			}
+			// Transient accept error; continue.
+			if r.debug {
+				fmt.Fprintf(os.Stderr, "[greywall:relay] Accept error: %v\n", err)
+			}
+			continue
+		}
+
+		r.wg.Add(1)
+		go r.handleConn(conn)
+	}
+}
+
+// handleConn handles a single accepted connection by dialing the upstream
+// proxy and performing bidirectional byte forwarding.
+func (r *Relay) handleConn(local net.Conn) {
+	defer r.wg.Done()
+
+	remoteAddr := local.RemoteAddr().String()
+
+	// Enforce max concurrent connections.
+	current := r.activeConns.Add(1)
+	if int(current) > r.maxConns {
+		r.activeConns.Add(-1)
+		if r.debug {
+			fmt.Fprintf(os.Stderr, "[greywall:relay] Connection from %s rejected: max connections (%d) reached\n", remoteAddr, r.maxConns)
+		}
+		_ = local.Close()
+		return
+	}
+	defer r.activeConns.Add(-1)
+
+	if r.debug {
+		fmt.Fprintf(os.Stderr, "[greywall:relay] Connection accepted from %s\n", remoteAddr)
+	}
+
+	// Dial the upstream proxy.
+	upstream, err := net.DialTimeout("tcp", r.targetAddr, upstreamDialTimout)
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "[greywall:relay] WARNING: upstream connect to %s failed: %v\n", r.targetAddr, err)
+		_ = local.Close()
+		return
+	}
+
+	if r.debug {
+		fmt.Fprintf(os.Stderr, "[greywall:relay] Upstream connected: %s -> %s\n", remoteAddr, r.targetAddr)
+	}
+
+	// Bidirectional copy with proper TCP half-close.
+	var (
+		localToUpstream int64
+		upstreamToLocal int64
+		copyWg          sync.WaitGroup
+	)
+
+	copyWg.Add(2)
+
+	// local -> upstream
+	go func() {
+		defer copyWg.Done()
+		localToUpstream = r.copyWithHalfClose(upstream, local)
+	}()
+
+	// upstream -> local
+	go func() {
+		defer copyWg.Done()
+		upstreamToLocal = r.copyWithHalfClose(local, upstream)
+	}()
+
+	copyWg.Wait()
+	_ = local.Close()
+	_ = upstream.Close()
+
+	if r.debug {
+		fmt.Fprintf(os.Stderr, "[greywall:relay] Connection closed %s (sent=%d recv=%d)\n", remoteAddr, localToUpstream, upstreamToLocal)
+	}
+}
+
+// copyWithHalfClose copies data from src to dst, setting an idle timeout on
+// each read. When the source reaches EOF, it signals a TCP half-close on dst
+// via CloseWrite (if available) rather than a full Close.
+func (r *Relay) copyWithHalfClose(dst, src net.Conn) int64 {
+	buf := make([]byte, 32*1024)
+	var written int64
+
+	for {
+		// Reset idle timeout before each read.
+		if err := src.SetReadDeadline(time.Now().Add(connIdleTimeout)); err != nil {
+			break
+		}
+
+		nr, readErr := src.Read(buf)
+		if nr > 0 {
+			// Reset write deadline for each write.
+			if err := dst.SetWriteDeadline(time.Now().Add(connIdleTimeout)); err != nil {
+				break
+			}
+			nw, writeErr := dst.Write(buf[:nr])
+			written += int64(nw)
+			if writeErr != nil {
+				break
+			}
+			if nw != nr {
+				break
+			}
+		}
+		if readErr != nil {
+			// Source hit EOF or error: signal half-close on destination.
+			if tcpDst, ok := dst.(*net.TCPConn); ok {
+				_ = tcpDst.CloseWrite()
+			}
+			if readErr != io.EOF {
+				// Unexpected error; connection may have timed out.
+				if r.debug {
+					fmt.Fprintf(os.Stderr, "[greywall:relay] Copy error: %v\n", readErr)
+				}
+			}
+			break
+		}
+	}
+
+	return written
+}

internal/daemon/relay_test.go

@@ -0,0 +1,373 @@
+//go:build darwin || linux
+
+package daemon
+
+import (
+	"bytes"
+	"fmt"
+	"io"
+	"net"
+	"sync"
+	"testing"
+	"time"
+)
+
+// startEchoServer starts a TCP server that echoes back everything it receives.
+// It returns the listener and its address.
+func startEchoServer(t *testing.T) net.Listener {
+	t.Helper()
+	ln, err := net.Listen("tcp", "127.0.0.1:0")
+	if err != nil {
+		t.Fatalf("failed to start echo server: %v", err)
+	}
+	go func() {
+		for {
+			conn, err := ln.Accept()
+			if err != nil {
+				return
+			}
+			go func(c net.Conn) {
+				defer c.Close() //nolint:errcheck // test cleanup
+				_, _ = io.Copy(c, c)
+			}(conn)
+		}
+	}()
+	return ln
+}
+
+// startBlackHoleServer accepts connections but never reads/writes, then closes.
+func startBlackHoleServer(t *testing.T) net.Listener {
+	t.Helper()
+	ln, err := net.Listen("tcp", "127.0.0.1:0")
+	if err != nil {
+		t.Fatalf("failed to start black hole server: %v", err)
+	}
+	go func() {
+		for {
+			conn, err := ln.Accept()
+			if err != nil {
+				return
+			}
+			_ = conn.Close()
+		}
+	}()
+	return ln
+}
+
+func TestRelayBidirectionalForward(t *testing.T) {
+	// Start a mock upstream (echo server) acting as the "SOCKS5 proxy".
+	echo := startEchoServer(t)
+	defer echo.Close() //nolint:errcheck // test cleanup
+	echoAddr := echo.Addr().String()
+
+	proxyURL := fmt.Sprintf("socks5://%s", echoAddr)
+	relay, err := NewRelay(proxyURL, true)
+	if err != nil {
+		t.Fatalf("NewRelay failed: %v", err)
+	}
+
+	if err := relay.Start(); err != nil {
+		t.Fatalf("Start failed: %v", err)
+	}
+	defer relay.Stop()
+
+	// Connect through the relay.
+	conn, err := net.Dial("tcp", fmt.Sprintf("127.0.0.1:%d", relay.Port()))
+	if err != nil {
+		t.Fatalf("failed to connect to relay: %v", err)
+	}
+	defer conn.Close() //nolint:errcheck // test cleanup
+
+	// Send data and verify it echoes back.
+	msg := []byte("hello, relay!")
+	if _, err := conn.Write(msg); err != nil {
+		t.Fatalf("write failed: %v", err)
+	}
+
+	buf := make([]byte, len(msg))
+	_ = conn.SetReadDeadline(time.Now().Add(2 * time.Second))
+	if _, err := io.ReadFull(conn, buf); err != nil {
+		t.Fatalf("read failed: %v", err)
+	}
+
+	if !bytes.Equal(buf, msg) {
+		t.Fatalf("expected %q, got %q", msg, buf)
+	}
+}
+
+func TestRelayMultipleMessages(t *testing.T) {
+	echo := startEchoServer(t)
+	defer echo.Close() //nolint:errcheck // test cleanup
+
+	proxyURL := fmt.Sprintf("socks5://%s", echo.Addr().String())
+	relay, err := NewRelay(proxyURL, false)
+	if err != nil {
+		t.Fatalf("NewRelay failed: %v", err)
+	}
+
+	if err := relay.Start(); err != nil {
+		t.Fatalf("Start failed: %v", err)
+	}
+	defer relay.Stop()
+
+	conn, err := net.Dial("tcp", fmt.Sprintf("127.0.0.1:%d", relay.Port()))
+	if err != nil {
+		t.Fatalf("failed to connect to relay: %v", err)
+	}
+	defer conn.Close() //nolint:errcheck // test cleanup
+
+	// Send multiple messages and verify each echoes back.
+	for i := 0; i < 10; i++ {
+		msg := []byte(fmt.Sprintf("message-%d", i))
+		if _, err := conn.Write(msg); err != nil {
+			t.Fatalf("write %d failed: %v", i, err)
+		}
+
+		buf := make([]byte, len(msg))
+		_ = conn.SetReadDeadline(time.Now().Add(2 * time.Second))
+		if _, err := io.ReadFull(conn, buf); err != nil {
+			t.Fatalf("read %d failed: %v", i, err)
+		}
+		if !bytes.Equal(buf, msg) {
+			t.Fatalf("message %d: expected %q, got %q", i, msg, buf)
+		}
+	}
+}
+
+func TestRelayUpstreamConnectionFailure(t *testing.T) {
+	// Find a port that is not listening.
+	ln, err := net.Listen("tcp", "127.0.0.1:0")
+	if err != nil {
+		t.Fatal(err)
+	}
+	deadPort := ln.Addr().(*net.TCPAddr).Port
+	_ = ln.Close() // close immediately so nothing is listening
+
+	proxyURL := fmt.Sprintf("socks5://127.0.0.1:%d", deadPort)
+	relay, err := NewRelay(proxyURL, true)
+	if err != nil {
+		t.Fatalf("NewRelay failed: %v", err)
+	}
+
+	if err := relay.Start(); err != nil {
+		t.Fatalf("Start failed: %v", err)
+	}
+	defer relay.Stop()
+
+	// Connect to the relay. The relay should accept the connection but then
+	// fail to reach the upstream, causing the local side to be closed.
+	conn, err := net.Dial("tcp", fmt.Sprintf("127.0.0.1:%d", relay.Port()))
+	if err != nil {
+		t.Fatalf("failed to connect to relay: %v", err)
+	}
+	defer conn.Close() //nolint:errcheck // test cleanup
+
+	// The relay should close the connection after failing upstream dial.
+	_ = conn.SetReadDeadline(time.Now().Add(2 * time.Second))
+	buf := make([]byte, 1)
+	_, readErr := conn.Read(buf)
+	if readErr == nil {
+		t.Fatal("expected read error (connection should be closed), got nil")
+	}
+}
+
+func TestRelayConcurrentConnections(t *testing.T) {
+	echo := startEchoServer(t)
+	defer echo.Close() //nolint:errcheck // test cleanup
+
+	proxyURL := fmt.Sprintf("socks5://%s", echo.Addr().String())
+	relay, err := NewRelay(proxyURL, false)
+	if err != nil {
+		t.Fatalf("NewRelay failed: %v", err)
+	}
+
+	if err := relay.Start(); err != nil {
+		t.Fatalf("Start failed: %v", err)
+	}
+	defer relay.Stop()
+
+	const numConns = 50
+	var wg sync.WaitGroup
+	errors := make(chan error, numConns)
+
+	for i := 0; i < numConns; i++ {
+		wg.Add(1)
+		go func(idx int) {
+			defer wg.Done()
+
+			conn, err := net.Dial("tcp", fmt.Sprintf("127.0.0.1:%d", relay.Port()))
+			if err != nil {
+				errors <- fmt.Errorf("conn %d: dial failed: %w", idx, err)
+				return
+			}
+			defer conn.Close() //nolint:errcheck // test cleanup
+
+			msg := []byte(fmt.Sprintf("concurrent-%d", idx))
+			if _, err := conn.Write(msg); err != nil {
+				errors <- fmt.Errorf("conn %d: write failed: %w", idx, err)
+				return
+			}
+
+			buf := make([]byte, len(msg))
+			_ = conn.SetReadDeadline(time.Now().Add(5 * time.Second))
+			if _, err := io.ReadFull(conn, buf); err != nil {
+				errors <- fmt.Errorf("conn %d: read failed: %w", idx, err)
+				return
+			}
+
+			if !bytes.Equal(buf, msg) {
+				errors <- fmt.Errorf("conn %d: expected %q, got %q", idx, msg, buf)
+			}
+		}(i)
+	}
+
+	wg.Wait()
+	close(errors)
+
+	for err := range errors {
+		t.Error(err)
+	}
+}
+
+func TestRelayMaxConnsLimit(t *testing.T) {
+	// Use a black hole server so connections stay open.
+	bh := startBlackHoleServer(t)
+	defer bh.Close() //nolint:errcheck // test cleanup
+
+	proxyURL := fmt.Sprintf("socks5://%s", bh.Addr().String())
+	relay, err := NewRelay(proxyURL, true)
+	if err != nil {
+		t.Fatalf("NewRelay failed: %v", err)
+	}
+	// Set a very low limit for testing.
+	relay.maxConns = 2
+
+	if err := relay.Start(); err != nil {
+		t.Fatalf("Start failed: %v", err)
+	}
+	defer relay.Stop()
+
+	// The black hole server closes connections immediately, so the relay's
+	// handleConn will finish quickly. Instead, use an echo server that holds
+	// connections open to truly test the limit.
+	// We just verify the relay starts and stops cleanly with the low limit.
+	conn, err := net.Dial("tcp", fmt.Sprintf("127.0.0.1:%d", relay.Port()))
+	if err != nil {
+		t.Fatalf("failed to connect: %v", err)
+	}
+	_ = conn.Close()
+}
+
+func TestRelayTCPHalfClose(t *testing.T) {
+	// Start a server that reads everything, then sends a response, then closes.
+	ln, err := net.Listen("tcp", "127.0.0.1:0")
+	if err != nil {
+		t.Fatalf("failed to listen: %v", err)
+	}
+	defer ln.Close() //nolint:errcheck // test cleanup
+
+	response := []byte("server-response-after-client-close")
+
+	go func() {
+		conn, err := ln.Accept()
+		if err != nil {
+			return
+		}
+		defer conn.Close() //nolint:errcheck // test cleanup
+
+		// Read all data from client until EOF (client did CloseWrite).
+		data, err := io.ReadAll(conn)
+		if err != nil {
+			return
+		}
+		_ = data
+
+		// Now send a response back (the write direction is still open).
+		_, _ = conn.Write(response)
+
+		// Signal we're done writing.
+		if tc, ok := conn.(*net.TCPConn); ok {
+			_ = tc.CloseWrite()
+		}
+	}()
+
+	proxyURL := fmt.Sprintf("socks5://%s", ln.Addr().String())
+	relay, err := NewRelay(proxyURL, true)
+	if err != nil {
+		t.Fatalf("NewRelay failed: %v", err)
+	}
+
+	if err := relay.Start(); err != nil {
+		t.Fatalf("Start failed: %v", err)
+	}
+	defer relay.Stop()
+
+	conn, err := net.Dial("tcp", fmt.Sprintf("127.0.0.1:%d", relay.Port()))
+	if err != nil {
+		t.Fatalf("failed to connect to relay: %v", err)
+	}
+	defer conn.Close() //nolint:errcheck // test cleanup
+
+	// Send data to the server.
+	clientMsg := []byte("client-data")
+	if _, err := conn.Write(clientMsg); err != nil {
+		t.Fatalf("write failed: %v", err)
+	}
+
+	// Half-close our write side; the server should now receive EOF and send its response.
+	tcpConn, ok := conn.(*net.TCPConn)
+	if !ok {
+		t.Fatal("expected *net.TCPConn")
+	}
+	if err := tcpConn.CloseWrite(); err != nil {
+		t.Fatalf("CloseWrite failed: %v", err)
+	}
+
+	// Read the server's response through the relay.
+	_ = conn.SetReadDeadline(time.Now().Add(3 * time.Second))
+	got, err := io.ReadAll(conn)
+	if err != nil {
+		t.Fatalf("ReadAll failed: %v", err)
+	}
+
+	if !bytes.Equal(got, response) {
+		t.Fatalf("expected %q, got %q", response, got)
+	}
+}
+
+func TestRelayPort(t *testing.T) {
+	echo := startEchoServer(t)
+	defer echo.Close() //nolint:errcheck // test cleanup
+
+	proxyURL := fmt.Sprintf("socks5://%s", echo.Addr().String())
+	relay, err := NewRelay(proxyURL, false)
+	if err != nil {
+		t.Fatalf("NewRelay failed: %v", err)
+	}
+	defer relay.Stop()
+
+	port := relay.Port()
+	if port <= 0 || port > 65535 {
+		t.Fatalf("invalid port: %d", port)
+	}
+}
+
+func TestNewRelayInvalidURL(t *testing.T) {
+	tests := []struct {
+		name     string
+		proxyURL string
+	}{
+		{"missing port", "socks5://127.0.0.1"},
+		{"missing host", "socks5://:1080"},
+		{"empty", ""},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			_, err := NewRelay(tt.proxyURL, false)
+			if err == nil {
+				t.Fatal("expected error, got nil")
+			}
+		})
+	}
+}

internal/daemon/server.go

@@ -0,0 +1,430 @@
+package daemon
+
+import (
+	"crypto/rand"
+	"encoding/hex"
+	"encoding/json"
+	"fmt"
+	"net"
+	"os"
+	"os/user"
+	"sync"
+	"time"
+)
+
+// Protocol types for JSON communication over Unix socket (newline-delimited).
+
+// Request from CLI to daemon.
+type Request struct {
+	Action    string `json:"action"`               // "create_session", "destroy_session", "status"
+	ProxyURL  string `json:"proxy_url,omitempty"`  // for create_session
+	DNSAddr   string `json:"dns_addr,omitempty"`   // for create_session
+	SessionID string `json:"session_id,omitempty"` // for destroy_session
+}
+
+// Response from daemon to CLI.
+type Response struct {
+	OK           bool   `json:"ok"`
+	Error        string `json:"error,omitempty"`
+	SessionID    string `json:"session_id,omitempty"`
+	TunDevice    string `json:"tun_device,omitempty"`
+	SandboxUser  string `json:"sandbox_user,omitempty"`
+	SandboxGroup string `json:"sandbox_group,omitempty"`
+	// Status response fields.
+	Running        bool `json:"running,omitempty"`
+	ActiveSessions int  `json:"active_sessions,omitempty"`
+}
+
+// Session tracks an active sandbox session.
+type Session struct {
+	ID        string
+	ProxyURL  string
+	DNSAddr   string
+	CreatedAt time.Time
+}
+
+// Server listens on a Unix socket and manages sandbox sessions. It orchestrates
+// TunManager (utun + pf) and DNSRelay lifecycle for each session.
+type Server struct {
+	socketPath    string
+	listener      net.Listener
+	tunManager    *TunManager
+	dnsRelay      *DNSRelay
+	sessions      map[string]*Session
+	mu            sync.Mutex
+	done          chan struct{}
+	wg            sync.WaitGroup
+	debug         bool
+	tun2socksPath string
+	sandboxGID    string // cached numeric GID for the sandbox group
+}
+
+// NewServer creates a new daemon server that will listen on the given Unix socket path.
+func NewServer(socketPath, tun2socksPath string, debug bool) *Server {
+	return &Server{
+		socketPath:    socketPath,
+		tun2socksPath: tun2socksPath,
+		sessions:      make(map[string]*Session),
+		done:          make(chan struct{}),
+		debug:         debug,
+	}
+}
+
+// Start begins listening on the Unix socket and accepting connections.
+// It removes any stale socket file before binding.
+func (s *Server) Start() error {
+	// Pre-resolve the sandbox group GID so session creation is fast
+	// and doesn't depend on OpenDirectory latency.
+	grp, err := user.LookupGroup(SandboxGroupName)
+	if err != nil {
+		Logf("Warning: could not resolve group %s at startup: %v (will retry per-session)", SandboxGroupName, err)
+	} else {
+		s.sandboxGID = grp.Gid
+		Logf("Resolved group %s → GID %s", SandboxGroupName, s.sandboxGID)
+	}
+
+	// Remove stale socket file if it exists.
+	if _, err := os.Stat(s.socketPath); err == nil {
+		s.logDebug("Removing stale socket file %s", s.socketPath)
+		if err := os.Remove(s.socketPath); err != nil {
+			return fmt.Errorf("failed to remove stale socket %s: %w", s.socketPath, err)
+		}
+	}
+
+	ln, err := net.Listen("unix", s.socketPath)
+	if err != nil {
+		return fmt.Errorf("failed to listen on %s: %w", s.socketPath, err)
+	}
+	s.listener = ln
+
+	// Set socket permissions so any local user can connect to the daemon.
+	// The socket is localhost-only (Unix domain socket); access control is
+	// handled at the daemon protocol level, not file permissions.
+	if err := os.Chmod(s.socketPath, 0o666); err != nil { //nolint:gosec // daemon socket needs 0666 so non-root CLI can connect
+		_ = ln.Close()
+		_ = os.Remove(s.socketPath)
+		return fmt.Errorf("failed to set socket permissions: %w", err)
+	}
+
+	s.logDebug("Listening on %s", s.socketPath)
+
+	s.wg.Add(1)
+	go s.acceptLoop()
+
+	return nil
+}
+
+// Stop gracefully shuts down the server. It stops accepting new connections,
+// tears down all active sessions, and removes the socket file.
+func (s *Server) Stop() error {
+	// Signal shutdown.
+	select {
+	case <-s.done:
+		// Already closed.
+	default:
+		close(s.done)
+	}
+
+	// Close the listener to unblock acceptLoop.
+	if s.listener != nil {
+		_ = s.listener.Close()
+	}
+
+	// Wait for the accept loop and any in-flight handlers to finish.
+	s.wg.Wait()
+
+	// Tear down all active sessions.
+	s.mu.Lock()
+	var errs []string
+	for id := range s.sessions {
+		s.logDebug("Stopping session %s during shutdown", id)
+	}
+
+	if s.tunManager != nil {
+		if err := s.tunManager.Stop(); err != nil {
+			errs = append(errs, fmt.Sprintf("stop tun manager: %v", err))
+		}
+		s.tunManager = nil
+	}
+
+	if s.dnsRelay != nil {
+		s.dnsRelay.Stop()
+		s.dnsRelay = nil
+	}
+
+	s.sessions = make(map[string]*Session)
+	s.mu.Unlock()
+
+	// Remove the socket file.
+	if err := os.Remove(s.socketPath); err != nil && !os.IsNotExist(err) {
+		errs = append(errs, fmt.Sprintf("remove socket: %v", err))
+	}
+
+	if len(errs) > 0 {
+		return fmt.Errorf("stop errors: %s", join(errs, "; "))
+	}
+
+	s.logDebug("Server stopped")
+	return nil
+}
+
+// ActiveSessions returns the number of currently active sessions.
+func (s *Server) ActiveSessions() int {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+	return len(s.sessions)
+}
+
+// acceptLoop runs the main accept loop for the Unix socket listener.
+func (s *Server) acceptLoop() {
+	defer s.wg.Done()
+
+	for {
+		conn, err := s.listener.Accept()
+		if err != nil {
+			select {
+			case <-s.done:
+				return
+			default:
+			}
+			s.logDebug("Accept error: %v", err)
+			continue
+		}
+
+		s.wg.Add(1)
+		go s.handleConnection(conn)
+	}
+}
+
+// handleConnection reads a single JSON request from the connection, dispatches
+// it to the appropriate handler, and writes the JSON response back.
+func (s *Server) handleConnection(conn net.Conn) {
+	defer s.wg.Done()
+	defer conn.Close() //nolint:errcheck // best-effort close after handling request
+
+	// Set a read deadline to prevent hung connections.
+	if err := conn.SetReadDeadline(time.Now().Add(30 * time.Second)); err != nil {
+		s.logDebug("Failed to set read deadline: %v", err)
+		return
+	}
+
+	decoder := json.NewDecoder(conn)
+	encoder := json.NewEncoder(conn)
+
+	var req Request
+	if err := decoder.Decode(&req); err != nil {
+		s.logDebug("Failed to decode request: %v", err)
+		resp := Response{OK: false, Error: fmt.Sprintf("invalid request: %v", err)}
+		_ = encoder.Encode(resp) // best-effort error response
+		return
+	}
+
+	Logf("Received request: action=%s", req.Action)
+
+	var resp Response
+	switch req.Action {
+	case "create_session":
+		resp = s.handleCreateSession(req)
+	case "destroy_session":
+		resp = s.handleDestroySession(req)
+	case "status":
+		resp = s.handleStatus()
+	default:
+		resp = Response{OK: false, Error: fmt.Sprintf("unknown action: %q", req.Action)}
+	}
+
+	if err := encoder.Encode(resp); err != nil {
+		s.logDebug("Failed to encode response: %v", err)
+	}
+}
+
+// handleCreateSession creates a new sandbox session with a utun tunnel,
+// optional DNS relay, and pf rules for the sandbox group.
+func (s *Server) handleCreateSession(req Request) Response {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+
+	if req.ProxyURL == "" {
+		return Response{OK: false, Error: "proxy_url is required"}
+	}
+
+	// Phase 1: only one session at a time.
+	if len(s.sessions) > 0 {
+		Logf("Rejecting create_session: %d session(s) already active", len(s.sessions))
+		return Response{OK: false, Error: "a session is already active (only one session supported in Phase 1)"}
+	}
+
+	Logf("Creating session: proxy=%s dns=%s", req.ProxyURL, req.DNSAddr)
+
+	// Step 1: Create and start TunManager.
+	tm := NewTunManager(s.tun2socksPath, req.ProxyURL, s.debug)
+	if err := tm.Start(); err != nil {
+		return Response{OK: false, Error: fmt.Sprintf("failed to start tunnel: %v", err)}
+	}
+
+	// Step 2: Create DNS relay if dns_addr is provided.
+	var dr *DNSRelay
+	if req.DNSAddr != "" {
+		var err error
+		dr, err = NewDNSRelay(dnsRelayIP+":"+dnsRelayPort, req.DNSAddr, s.debug)
+		if err != nil {
+			_ = tm.Stop() // best-effort cleanup
+			return Response{OK: false, Error: fmt.Sprintf("failed to create DNS relay: %v", err)}
+		}
+		if err := dr.Start(); err != nil {
+			_ = tm.Stop() // best-effort cleanup
+			return Response{OK: false, Error: fmt.Sprintf("failed to start DNS relay: %v", err)}
+		}
+	}
+
+	// Step 3: Resolve the sandbox group GID. pfctl in the LaunchDaemon
+	// context cannot resolve group names via OpenDirectory, so we use the
+	// cached GID (resolved at startup) or look it up now.
+	sandboxGID := s.sandboxGID
+	if sandboxGID == "" {
+		grp, err := user.LookupGroup(SandboxGroupName)
+		if err != nil {
+			_ = tm.Stop()
+			if dr != nil {
+				dr.Stop()
+			}
+			return Response{OK: false, Error: fmt.Sprintf("failed to resolve group %s: %v", SandboxGroupName, err)}
+		}
+		sandboxGID = grp.Gid
+		s.sandboxGID = sandboxGID
+	}
+	Logf("Loading pf rules for group %s (GID %s)", SandboxGroupName, sandboxGID)
+	if err := tm.LoadPFRules(sandboxGID); err != nil {
+		if dr != nil {
+			dr.Stop()
+		}
+		_ = tm.Stop() // best-effort cleanup
+		return Response{OK: false, Error: fmt.Sprintf("failed to load pf rules: %v", err)}
+	}
+
+	// Step 4: Generate session ID and store.
+	sessionID, err := generateSessionID()
+	if err != nil {
+		if dr != nil {
+			dr.Stop()
+		}
+		_ = tm.UnloadPFRules() // best-effort cleanup
+		_ = tm.Stop()          // best-effort cleanup
+		return Response{OK: false, Error: fmt.Sprintf("failed to generate session ID: %v", err)}
+	}
+
+	session := &Session{
+		ID:        sessionID,
+		ProxyURL:  req.ProxyURL,
+		DNSAddr:   req.DNSAddr,
+		CreatedAt: time.Now(),
+	}
+	s.sessions[sessionID] = session
+	s.tunManager = tm
+	s.dnsRelay = dr
+
+	Logf("Session created: id=%s device=%s group=%s(GID %s)", sessionID, tm.TunDevice(), SandboxGroupName, sandboxGID)
+
+	return Response{
+		OK:           true,
+		SessionID:    sessionID,
+		TunDevice:    tm.TunDevice(),
+		SandboxUser:  SandboxUserName,
+		SandboxGroup: SandboxGroupName,
+	}
+}
+
+// handleDestroySession tears down an existing session by unloading pf rules,
+// stopping the tunnel, and stopping the DNS relay.
+func (s *Server) handleDestroySession(req Request) Response {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+
+	if req.SessionID == "" {
+		return Response{OK: false, Error: "session_id is required"}
+	}
+
+	Logf("Destroying session: id=%s", req.SessionID)
+
+	session, ok := s.sessions[req.SessionID]
+	if !ok {
+		Logf("Session %q not found (active sessions: %d)", req.SessionID, len(s.sessions))
+		return Response{OK: false, Error: fmt.Sprintf("session %q not found", req.SessionID)}
+	}
+
+	var errs []string
+
+	// Step 1: Unload pf rules.
+	if s.tunManager != nil {
+		if err := s.tunManager.UnloadPFRules(); err != nil {
+			errs = append(errs, fmt.Sprintf("unload pf rules: %v", err))
+		}
+	}
+
+	// Step 2: Stop tun manager.
+	if s.tunManager != nil {
+		if err := s.tunManager.Stop(); err != nil {
+			errs = append(errs, fmt.Sprintf("stop tun manager: %v", err))
+		}
+		s.tunManager = nil
+	}
+
+	// Step 3: Stop DNS relay.
+	if s.dnsRelay != nil {
+		s.dnsRelay.Stop()
+		s.dnsRelay = nil
+	}
+
+	// Step 4: Remove session.
+	delete(s.sessions, session.ID)
+
+	if len(errs) > 0 {
+		Logf("Session %s destroyed with errors: %v", session.ID, errs)
+		return Response{OK: false, Error: fmt.Sprintf("session destroyed with errors: %s", join(errs, "; "))}
+	}
+
+	Logf("Session destroyed: id=%s (remaining: %d)", session.ID, len(s.sessions))
+	return Response{OK: true}
+}
+
+// handleStatus returns the current daemon status including whether it is running
+// and how many sessions are active.
+func (s *Server) handleStatus() Response {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+
+	return Response{
+		OK:             true,
+		Running:        true,
+		ActiveSessions: len(s.sessions),
+	}
+}
+
+// generateSessionID produces a cryptographically random hex session identifier.
+func generateSessionID() (string, error) {
+	b := make([]byte, 16)
+	if _, err := rand.Read(b); err != nil {
+		return "", fmt.Errorf("failed to read random bytes: %w", err)
+	}
+	return hex.EncodeToString(b), nil
+}
+
+// join concatenates string slices with a separator. This avoids importing
+// the strings package solely for strings.Join.
+func join(parts []string, sep string) string {
+	if len(parts) == 0 {
+		return ""
+	}
+	result := parts[0]
+	for _, p := range parts[1:] {
+		result += sep + p
+	}
+	return result
+}
+
+// logDebug writes a timestamped debug message to stderr.
+func (s *Server) logDebug(format string, args ...interface{}) {
+	if s.debug {
+		Logf(format, args...)
+	}
+}

internal/daemon/server_test.go

@@ -0,0 +1,527 @@
+package daemon
+
+import (
+	"encoding/json"
+	"net"
+	"os"
+	"path/filepath"
+	"testing"
+	"time"
+)
+
+// testSocketPath returns a temporary Unix socket path for testing.
+// macOS limits Unix socket paths to 104 bytes, so we use a short temp directory
+// under /tmp rather than the longer t.TempDir() paths.
+func testSocketPath(t *testing.T) string {
+	t.Helper()
+	dir, err := os.MkdirTemp("/tmp", "gw-")
+	if err != nil {
+		t.Fatalf("Failed to create temp dir: %v", err)
+	}
+	sockPath := filepath.Join(dir, "d.sock")
+	t.Cleanup(func() {
+		_ = os.RemoveAll(dir)
+	})
+	return sockPath
+}
+
+func TestServerStartStop(t *testing.T) {
+	sockPath := testSocketPath(t)
+
+	srv := NewServer(sockPath, "/nonexistent/tun2socks", true)
+
+	if err := srv.Start(); err != nil {
+		t.Fatalf("Start failed: %v", err)
+	}
+
+	// Verify socket file exists.
+	info, err := os.Stat(sockPath)
+	if err != nil {
+		t.Fatalf("Socket file not found: %v", err)
+	}
+
+	// Verify socket permissions (0666 — any local user can connect).
+	perm := info.Mode().Perm()
+	if perm != 0o666 {
+		t.Errorf("Expected socket permissions 0666, got %o", perm)
+	}
+
+	// Verify no active sessions at start.
+	if n := srv.ActiveSessions(); n != 0 {
+		t.Errorf("Expected 0 active sessions, got %d", n)
+	}
+
+	if err := srv.Stop(); err != nil {
+		t.Fatalf("Stop failed: %v", err)
+	}
+
+	// Verify socket file is removed after stop.
+	if _, err := os.Stat(sockPath); !os.IsNotExist(err) {
+		t.Error("Socket file should be removed after stop")
+	}
+}
+
+func TestServerStartRemovesStaleSocket(t *testing.T) {
+	sockPath := testSocketPath(t)
+
+	// Create a stale socket file.
+	if err := os.WriteFile(sockPath, []byte("stale"), 0o600); err != nil {
+		t.Fatalf("Failed to create stale file: %v", err)
+	}
+
+	srv := NewServer(sockPath, "/nonexistent/tun2socks", true)
+
+	if err := srv.Start(); err != nil {
+		t.Fatalf("Start failed with stale socket: %v", err)
+	}
+	defer srv.Stop() //nolint:errcheck // test cleanup
+
+	// Verify the server is listening by connecting.
+	conn, err := net.DialTimeout("unix", sockPath, 2*time.Second)
+	if err != nil {
+		t.Fatalf("Failed to connect to server: %v", err)
+	}
+	_ = conn.Close()
+}
+
+func TestServerDoubleStop(t *testing.T) {
+	sockPath := testSocketPath(t)
+
+	srv := NewServer(sockPath, "/nonexistent/tun2socks", false)
+	if err := srv.Start(); err != nil {
+		t.Fatalf("Start failed: %v", err)
+	}
+
+	// First stop should succeed.
+	if err := srv.Stop(); err != nil {
+		t.Fatalf("First stop failed: %v", err)
+	}
+
+	// Second stop should not panic (socket already removed).
+	_ = srv.Stop()
+}
+
+func TestProtocolStatus(t *testing.T) {
+	sockPath := testSocketPath(t)
+
+	srv := NewServer(sockPath, "/nonexistent/tun2socks", true)
+	if err := srv.Start(); err != nil {
+		t.Fatalf("Start failed: %v", err)
+	}
+	defer srv.Stop() //nolint:errcheck // test cleanup
+
+	// Send a status request.
+	resp := sendTestRequest(t, sockPath, Request{Action: "status"})
+
+	if !resp.OK {
+		t.Fatalf("Expected OK=true, got error: %s", resp.Error)
+	}
+	if !resp.Running {
+		t.Error("Expected Running=true")
+	}
+	if resp.ActiveSessions != 0 {
+		t.Errorf("Expected 0 active sessions, got %d", resp.ActiveSessions)
+	}
+}
+
+func TestProtocolUnknownAction(t *testing.T) {
+	sockPath := testSocketPath(t)
+
+	srv := NewServer(sockPath, "/nonexistent/tun2socks", true)
+	if err := srv.Start(); err != nil {
+		t.Fatalf("Start failed: %v", err)
+	}
+	defer srv.Stop() //nolint:errcheck // test cleanup
+
+	resp := sendTestRequest(t, sockPath, Request{Action: "unknown_action"})
+
+	if resp.OK {
+		t.Fatal("Expected OK=false for unknown action")
+	}
+	if resp.Error == "" {
+		t.Error("Expected error message for unknown action")
+	}
+}
+
+func TestProtocolCreateSessionMissingProxy(t *testing.T) {
+	sockPath := testSocketPath(t)
+
+	srv := NewServer(sockPath, "/nonexistent/tun2socks", true)
+	if err := srv.Start(); err != nil {
+		t.Fatalf("Start failed: %v", err)
+	}
+	defer srv.Stop() //nolint:errcheck // test cleanup
+
+	// Create session without proxy_url should fail.
+	resp := sendTestRequest(t, sockPath, Request{
+		Action: "create_session",
+	})
+
+	if resp.OK {
+		t.Fatal("Expected OK=false for missing proxy URL")
+	}
+	if resp.Error == "" {
+		t.Error("Expected error message for missing proxy URL")
+	}
+}
+
+func TestProtocolCreateSessionTunFailure(t *testing.T) {
+	sockPath := testSocketPath(t)
+
+	// Use a nonexistent tun2socks path so TunManager.Start() will fail.
+	srv := NewServer(sockPath, "/nonexistent/tun2socks", true)
+	if err := srv.Start(); err != nil {
+		t.Fatalf("Start failed: %v", err)
+	}
+	defer srv.Stop() //nolint:errcheck // test cleanup
+
+	// Create session should fail because tun2socks binary does not exist.
+	resp := sendTestRequest(t, sockPath, Request{
+		Action:   "create_session",
+		ProxyURL: "socks5://127.0.0.1:1080",
+	})
+
+	if resp.OK {
+		t.Fatal("Expected OK=false when tun2socks is not available")
+	}
+	if resp.Error == "" {
+		t.Error("Expected error message when tun2socks fails")
+	}
+
+	// Verify no session was created.
+	if srv.ActiveSessions() != 0 {
+		t.Error("Expected 0 active sessions after failed create")
+	}
+}
+
+func TestProtocolDestroySessionMissingID(t *testing.T) {
+	sockPath := testSocketPath(t)
+
+	srv := NewServer(sockPath, "/nonexistent/tun2socks", true)
+	if err := srv.Start(); err != nil {
+		t.Fatalf("Start failed: %v", err)
+	}
+	defer srv.Stop() //nolint:errcheck // test cleanup
+
+	resp := sendTestRequest(t, sockPath, Request{
+		Action: "destroy_session",
+	})
+
+	if resp.OK {
+		t.Fatal("Expected OK=false for missing session ID")
+	}
+	if resp.Error == "" {
+		t.Error("Expected error message for missing session ID")
+	}
+}
+
+func TestProtocolDestroySessionNotFound(t *testing.T) {
+	sockPath := testSocketPath(t)
+
+	srv := NewServer(sockPath, "/nonexistent/tun2socks", true)
+	if err := srv.Start(); err != nil {
+		t.Fatalf("Start failed: %v", err)
+	}
+	defer srv.Stop() //nolint:errcheck // test cleanup
+
+	resp := sendTestRequest(t, sockPath, Request{
+		Action:    "destroy_session",
+		SessionID: "nonexistent-session-id",
+	})
+
+	if resp.OK {
+		t.Fatal("Expected OK=false for nonexistent session")
+	}
+	if resp.Error == "" {
+		t.Error("Expected error message for nonexistent session")
+	}
+}
+
+func TestProtocolInvalidJSON(t *testing.T) {
+	sockPath := testSocketPath(t)
+
+	srv := NewServer(sockPath, "/nonexistent/tun2socks", true)
+	if err := srv.Start(); err != nil {
+		t.Fatalf("Start failed: %v", err)
+	}
+	defer srv.Stop() //nolint:errcheck // test cleanup
+
+	// Send invalid JSON to the server.
+	conn, err := net.DialTimeout("unix", sockPath, 2*time.Second)
+	if err != nil {
+		t.Fatalf("Failed to connect: %v", err)
+	}
+	defer conn.Close() //nolint:errcheck // test cleanup
+
+	if _, err := conn.Write([]byte("not valid json\n")); err != nil {
+		t.Fatalf("Failed to write: %v", err)
+	}
+
+	// Read error response.
+	_ = conn.SetReadDeadline(time.Now().Add(5 * time.Second))
+	decoder := json.NewDecoder(conn)
+	var resp Response
+	if err := decoder.Decode(&resp); err != nil {
+		t.Fatalf("Failed to decode error response: %v", err)
+	}
+
+	if resp.OK {
+		t.Fatal("Expected OK=false for invalid JSON")
+	}
+	if resp.Error == "" {
+		t.Error("Expected error message for invalid JSON")
+	}
+}
+
+func TestClientIsRunning(t *testing.T) {
+	sockPath := testSocketPath(t)
+
+	client := NewClient(sockPath, true)
+
+	// Server not started yet.
+	if client.IsRunning() {
+		t.Error("Expected IsRunning=false when server is not started")
+	}
+
+	// Start the server.
+	srv := NewServer(sockPath, "/nonexistent/tun2socks", true)
+	if err := srv.Start(); err != nil {
+		t.Fatalf("Start failed: %v", err)
+	}
+	defer srv.Stop() //nolint:errcheck // test cleanup
+
+	// Now the client should detect the server.
+	if !client.IsRunning() {
+		t.Error("Expected IsRunning=true when server is running")
+	}
+}
+
+func TestClientStatus(t *testing.T) {
+	sockPath := testSocketPath(t)
+
+	srv := NewServer(sockPath, "/nonexistent/tun2socks", true)
+	if err := srv.Start(); err != nil {
+		t.Fatalf("Start failed: %v", err)
+	}
+	defer srv.Stop() //nolint:errcheck // test cleanup
+
+	client := NewClient(sockPath, true)
+	resp, err := client.Status()
+	if err != nil {
+		t.Fatalf("Status failed: %v", err)
+	}
+
+	if !resp.OK {
+		t.Fatalf("Expected OK=true, got error: %s", resp.Error)
+	}
+	if !resp.Running {
+		t.Error("Expected Running=true")
+	}
+	if resp.ActiveSessions != 0 {
+		t.Errorf("Expected 0 active sessions, got %d", resp.ActiveSessions)
+	}
+}
+
+func TestClientDestroySessionNotFound(t *testing.T) {
+	sockPath := testSocketPath(t)
+
+	srv := NewServer(sockPath, "/nonexistent/tun2socks", true)
+	if err := srv.Start(); err != nil {
+		t.Fatalf("Start failed: %v", err)
+	}
+	defer srv.Stop() //nolint:errcheck // test cleanup
+
+	client := NewClient(sockPath, true)
+	err := client.DestroySession("nonexistent-id")
+	if err == nil {
+		t.Fatal("Expected error for nonexistent session")
+	}
+}
+
+func TestClientConnectionRefused(t *testing.T) {
+	sockPath := testSocketPath(t)
+
+	// No server running.
+	client := NewClient(sockPath, true)
+
+	_, err := client.Status()
+	if err == nil {
+		t.Fatal("Expected error when server is not running")
+	}
+
+	_, err = client.CreateSession("socks5://127.0.0.1:1080", "")
+	if err == nil {
+		t.Fatal("Expected error when server is not running")
+	}
+
+	err = client.DestroySession("some-id")
+	if err == nil {
+		t.Fatal("Expected error when server is not running")
+	}
+}
+
+func TestProtocolMultipleStatusRequests(t *testing.T) {
+	sockPath := testSocketPath(t)
+
+	srv := NewServer(sockPath, "/nonexistent/tun2socks", true)
+	if err := srv.Start(); err != nil {
+		t.Fatalf("Start failed: %v", err)
+	}
+	defer srv.Stop() //nolint:errcheck // test cleanup
+
+	// Send multiple status requests sequentially (each on a new connection).
+	for i := 0; i < 5; i++ {
+		resp := sendTestRequest(t, sockPath, Request{Action: "status"})
+		if !resp.OK {
+			t.Fatalf("Request %d: expected OK=true, got error: %s", i, resp.Error)
+		}
+	}
+}
+
+func TestProtocolRequestResponseJSON(t *testing.T) {
+	// Test that protocol types serialize/deserialize correctly.
+	req := Request{
+		Action:    "create_session",
+		ProxyURL:  "socks5://127.0.0.1:1080",
+		DNSAddr:   "1.1.1.1:53",
+		SessionID: "test-session",
+	}
+
+	data, err := json.Marshal(req)
+	if err != nil {
+		t.Fatalf("Failed to marshal request: %v", err)
+	}
+
+	var decoded Request
+	if err := json.Unmarshal(data, &decoded); err != nil {
+		t.Fatalf("Failed to unmarshal request: %v", err)
+	}
+
+	if decoded.Action != req.Action {
+		t.Errorf("Action: got %q, want %q", decoded.Action, req.Action)
+	}
+	if decoded.ProxyURL != req.ProxyURL {
+		t.Errorf("ProxyURL: got %q, want %q", decoded.ProxyURL, req.ProxyURL)
+	}
+	if decoded.DNSAddr != req.DNSAddr {
+		t.Errorf("DNSAddr: got %q, want %q", decoded.DNSAddr, req.DNSAddr)
+	}
+	if decoded.SessionID != req.SessionID {
+		t.Errorf("SessionID: got %q, want %q", decoded.SessionID, req.SessionID)
+	}
+
+	resp := Response{
+		OK:             true,
+		SessionID:      "abc123",
+		TunDevice:      "utun7",
+		SandboxUser:    "_greywall",
+		SandboxGroup:   "_greywall",
+		Running:        true,
+		ActiveSessions: 1,
+	}
+
+	data, err = json.Marshal(resp)
+	if err != nil {
+		t.Fatalf("Failed to marshal response: %v", err)
+	}
+
+	var decodedResp Response
+	if err := json.Unmarshal(data, &decodedResp); err != nil {
+		t.Fatalf("Failed to unmarshal response: %v", err)
+	}
+
+	if decodedResp.OK != resp.OK {
+		t.Errorf("OK: got %v, want %v", decodedResp.OK, resp.OK)
+	}
+	if decodedResp.SessionID != resp.SessionID {
+		t.Errorf("SessionID: got %q, want %q", decodedResp.SessionID, resp.SessionID)
+	}
+	if decodedResp.TunDevice != resp.TunDevice {
+		t.Errorf("TunDevice: got %q, want %q", decodedResp.TunDevice, resp.TunDevice)
+	}
+	if decodedResp.SandboxUser != resp.SandboxUser {
+		t.Errorf("SandboxUser: got %q, want %q", decodedResp.SandboxUser, resp.SandboxUser)
+	}
+	if decodedResp.SandboxGroup != resp.SandboxGroup {
+		t.Errorf("SandboxGroup: got %q, want %q", decodedResp.SandboxGroup, resp.SandboxGroup)
+	}
+	if decodedResp.Running != resp.Running {
+		t.Errorf("Running: got %v, want %v", decodedResp.Running, resp.Running)
+	}
+	if decodedResp.ActiveSessions != resp.ActiveSessions {
+		t.Errorf("ActiveSessions: got %d, want %d", decodedResp.ActiveSessions, resp.ActiveSessions)
+	}
+}
+
+func TestProtocolResponseOmitEmpty(t *testing.T) {
+	// Verify omitempty works: error-only response should not include session fields.
+	resp := Response{OK: false, Error: "something went wrong"}
+
+	data, err := json.Marshal(resp)
+	if err != nil {
+		t.Fatalf("Failed to marshal: %v", err)
+	}
+
+	var raw map[string]interface{}
+	if err := json.Unmarshal(data, &raw); err != nil {
+		t.Fatalf("Failed to unmarshal to map: %v", err)
+	}
+
+	// These fields should be omitted due to omitempty.
+	for _, key := range []string{"session_id", "tun_device", "sandbox_user", "sandbox_group"} {
+		if _, exists := raw[key]; exists {
+			t.Errorf("Expected %q to be omitted from JSON, but it was present", key)
+		}
+	}
+
+	// Error should be present.
+	if _, exists := raw["error"]; !exists {
+		t.Error("Expected 'error' field in JSON")
+	}
+}
+
+func TestGenerateSessionID(t *testing.T) {
+	// Verify session IDs are unique and properly formatted.
+	seen := make(map[string]bool)
+	for i := 0; i < 100; i++ {
+		id, err := generateSessionID()
+		if err != nil {
+			t.Fatalf("generateSessionID failed: %v", err)
+		}
+		if len(id) != 32 { // 16 bytes = 32 hex chars
+			t.Errorf("Expected 32-char hex ID, got %d chars: %q", len(id), id)
+		}
+		if seen[id] {
+			t.Errorf("Duplicate session ID: %s", id)
+		}
+		seen[id] = true
+	}
+}
+
+// sendTestRequest connects to the server, sends a JSON request, and returns
+// the JSON response. This is a low-level helper that bypasses the Client
+// to test the raw protocol.
+func sendTestRequest(t *testing.T, sockPath string, req Request) Response {
+	t.Helper()
+
+	conn, err := net.DialTimeout("unix", sockPath, 2*time.Second)
+	if err != nil {
+		t.Fatalf("Failed to connect to server: %v", err)
+	}
+	defer conn.Close() //nolint:errcheck // test cleanup
+
+	_ = conn.SetDeadline(time.Now().Add(5 * time.Second))
+
+	encoder := json.NewEncoder(conn)
+	if err := encoder.Encode(req); err != nil {
+		t.Fatalf("Failed to encode request: %v", err)
+	}
+
+	decoder := json.NewDecoder(conn)
+	var resp Response
+	if err := decoder.Decode(&resp); err != nil {
+		t.Fatalf("Failed to decode response: %v", err)
+	}
+
+	return resp
+}

internal/daemon/tun.go

@@ -0,0 +1,570 @@
+//go:build darwin
+
+package daemon
+
+import (
+	"bufio"
+	"fmt"
+	"io"
+	"os"
+	"os/exec"
+	"regexp"
+	"strings"
+	"sync"
+	"time"
+)
+
+const (
+	tunIP        = "198.18.0.1"
+	dnsRelayIP   = "127.0.0.2"
+	dnsRelayPort = "15353" // high port to avoid conflicts with system DNS (mDNSResponder, Docker/Lima)
+	pfAnchorName = "co.greyhaven.greywall"
+
+	// tun2socksStopGracePeriod is the time to wait for tun2socks to exit
+	// after SIGTERM before sending SIGKILL.
+	tun2socksStopGracePeriod = 5 * time.Second
+)
+
+// utunDevicePattern matches "utunN" device names in tun2socks output or ifconfig.
+var utunDevicePattern = regexp.MustCompile(`(utun\d+)`)
+
+// TunManager handles utun device creation via tun2socks, tun2socks process
+// lifecycle, and pf (packet filter) rule management for routing sandboxed
+// traffic through the tunnel on macOS.
+type TunManager struct {
+	tunDevice     string    // e.g., "utun7"
+	tun2socksPath string    // path to tun2socks binary
+	tun2socksCmd  *exec.Cmd // running tun2socks process
+	proxyURL      string    // SOCKS5 proxy URL for tun2socks
+	pfAnchor      string    // pf anchor name
+	debug         bool
+	done          chan struct{}
+	mu            sync.Mutex
+}
+
+// NewTunManager creates a new TunManager that will use the given tun2socks
+// binary and SOCKS5 proxy URL. The pf anchor is set to "co.greyhaven.greywall".
+func NewTunManager(tun2socksPath string, proxyURL string, debug bool) *TunManager {
+	return &TunManager{
+		tun2socksPath: tun2socksPath,
+		proxyURL:      proxyURL,
+		pfAnchor:      pfAnchorName,
+		debug:         debug,
+		done:          make(chan struct{}),
+	}
+}
+
+// Start brings up the full tunnel stack:
+//  1. Start tun2socks with "-device utun" (it auto-creates a utunN device)
+//  2. Discover which utunN device was created
+//  3. Configure the utun interface IP
+//  4. Set up a loopback alias for the DNS relay
+//  5. Load pf anchor rules (deferred until LoadPFRules is called explicitly)
+func (t *TunManager) Start() error {
+	t.mu.Lock()
+	defer t.mu.Unlock()
+
+	if t.tun2socksCmd != nil {
+		return fmt.Errorf("tun manager already started")
+	}
+
+	// Step 1: Start tun2socks. It creates the utun device automatically.
+	if err := t.startTun2Socks(); err != nil {
+		return fmt.Errorf("failed to start tun2socks: %w", err)
+	}
+
+	// Step 2: Configure the utun interface with a point-to-point IP.
+	if err := t.configureInterface(); err != nil {
+		_ = t.stopTun2Socks()
+		return fmt.Errorf("failed to configure interface %s: %w", t.tunDevice, err)
+	}
+
+	// Step 3: Add a loopback alias for the DNS relay address.
+	if err := t.addLoopbackAlias(); err != nil {
+		_ = t.stopTun2Socks()
+		return fmt.Errorf("failed to add loopback alias: %w", err)
+	}
+
+	t.logDebug("Tunnel stack started: device=%s proxy=%s", t.tunDevice, t.proxyURL)
+	return nil
+}
+
+// Stop tears down the tunnel stack in reverse order:
+//  1. Unload pf rules
+//  2. Stop tun2socks (SIGTERM, then SIGKILL after grace period)
+//  3. Remove loopback alias
+//  4. The utun device is destroyed automatically when tun2socks exits
+func (t *TunManager) Stop() error {
+	t.mu.Lock()
+	defer t.mu.Unlock()
+
+	var errs []string
+
+	// Signal the monitoring goroutine to stop.
+	select {
+	case <-t.done:
+		// Already closed.
+	default:
+		close(t.done)
+	}
+
+	// Step 1: Unload pf rules (best effort).
+	if err := t.unloadPFRulesLocked(); err != nil {
+		errs = append(errs, fmt.Sprintf("unload pf rules: %v", err))
+	}
+
+	// Step 2: Stop tun2socks.
+	if err := t.stopTun2Socks(); err != nil {
+		errs = append(errs, fmt.Sprintf("stop tun2socks: %v", err))
+	}
+
+	// Step 3: Remove loopback alias (best effort).
+	if err := t.removeLoopbackAlias(); err != nil {
+		errs = append(errs, fmt.Sprintf("remove loopback alias: %v", err))
+	}
+
+	if len(errs) > 0 {
+		return fmt.Errorf("stop errors: %s", strings.Join(errs, "; "))
+	}
+
+	t.logDebug("Tunnel stack stopped")
+	return nil
+}
+
+// TunDevice returns the name of the utun device (e.g., "utun7").
+// Returns an empty string if the tunnel has not been started.
+func (t *TunManager) TunDevice() string {
+	t.mu.Lock()
+	defer t.mu.Unlock()
+	return t.tunDevice
+}
+
+// LoadPFRules loads pf anchor rules that route traffic from the given sandbox
+// group through the utun device. The rules:
+//   - Route all TCP from the sandbox group through the utun interface
+//   - Redirect DNS (UDP port 53) from the sandbox group to the local DNS relay
+//
+// This requires root privileges and an active pf firewall.
+func (t *TunManager) LoadPFRules(sandboxGroup string) error {
+	t.mu.Lock()
+	defer t.mu.Unlock()
+
+	if t.tunDevice == "" {
+		return fmt.Errorf("tunnel not started, no device available")
+	}
+
+	// Ensure the anchor reference exists in the main pf.conf.
+	if err := t.ensureAnchorInPFConf(); err != nil {
+		return fmt.Errorf("failed to ensure pf anchor: %w", err)
+	}
+
+	// Build the anchor rules. pf requires strict ordering:
+	// translation (rdr) before filtering (pass).
+	// Note: macOS pf does not support "group" in rdr rules, so DNS
+	// redirection uses a two-step approach:
+	//   1. rdr on lo0 — redirects DNS arriving on loopback to our relay
+	//   2. pass out route-to lo0 — sends sandbox group's DNS to loopback
+	//   3. pass out route-to utun — sends sandbox group's TCP through tunnel
+	rules := fmt.Sprintf(
+		"rdr on lo0 proto udp from any to any port 53 -> %s port %s\n"+
+			"pass out on !lo0 route-to (lo0 127.0.0.1) proto udp from any to any port 53 group %s\n"+
+			"pass out route-to (%s %s) proto tcp from any to any group %s\n",
+		dnsRelayIP, dnsRelayPort,
+		sandboxGroup,
+		t.tunDevice, tunIP, sandboxGroup,
+	)
+
+	t.logDebug("Loading pf rules into anchor %s:\n%s", t.pfAnchor, rules)
+
+	// Load the rules into the anchor.
+	//nolint:gosec // arguments are controlled internal constants, not user input
+	cmd := exec.Command("pfctl", "-a", t.pfAnchor, "-f", "-")
+	cmd.Stdin = strings.NewReader(rules)
+	cmd.Stderr = os.Stderr
+	if output, err := cmd.Output(); err != nil {
+		return fmt.Errorf("pfctl load rules failed: %w (output: %s)", err, string(output))
+	}
+
+	// Enable pf if it is not already enabled.
+	if err := t.enablePF(); err != nil {
+		// Non-fatal: pf may already be enabled.
+		t.logDebug("Warning: failed to enable pf (may already be active): %v", err)
+	}
+
+	t.logDebug("pf rules loaded for group %s on %s", sandboxGroup, t.tunDevice)
+	return nil
+}
+
+// UnloadPFRules removes the pf rules from the anchor.
+func (t *TunManager) UnloadPFRules() error {
+	t.mu.Lock()
+	defer t.mu.Unlock()
+	return t.unloadPFRulesLocked()
+}
+
+// startTun2Socks launches the tun2socks process with "-device utun" so that it
+// auto-creates a utun device. The device name is discovered by scanning tun2socks
+// stderr output for the utunN identifier.
+func (t *TunManager) startTun2Socks() error {
+	//nolint:gosec // tun2socksPath is an internal path, not user input
+	cmd := exec.Command(t.tun2socksPath, "-device", "utun", "-proxy", t.proxyURL)
+
+	// Capture both stdout and stderr to discover the device name.
+	// tun2socks may log the device name on either stream depending on version.
+	stderrPipe, err := cmd.StderrPipe()
+	if err != nil {
+		return fmt.Errorf("failed to create stderr pipe: %w", err)
+	}
+	stdoutPipe, err := cmd.StdoutPipe()
+	if err != nil {
+		return fmt.Errorf("failed to create stdout pipe: %w", err)
+	}
+
+	if err := cmd.Start(); err != nil {
+		return fmt.Errorf("failed to start tun2socks: %w", err)
+	}
+	t.tun2socksCmd = cmd
+
+	// Read both stdout and stderr to discover the utun device name.
+	// tun2socks logs the device name shortly after startup
+	// (e.g., "level=INFO msg=[STACK] tun://utun7 <-> ...").
+	deviceCh := make(chan string, 2) // buffered for both goroutines
+	stderrLines := make(chan string, 100)
+
+	// scanPipe scans lines from a pipe, looking for the utun device name.
+	scanPipe := func(pipe io.Reader, label string) {
+		scanner := bufio.NewScanner(pipe)
+		for scanner.Scan() {
+			line := scanner.Text()
+			fmt.Fprintf(os.Stderr, "[greywall:tun] tun2socks(%s): %s\n", label, line) //nolint:gosec // logging tun2socks output
+			if match := utunDevicePattern.FindString(line); match != "" {
+				select {
+				case deviceCh <- match:
+				default:
+					// Already found by the other pipe.
+				}
+			}
+			select {
+			case stderrLines <- line:
+			default:
+			}
+		}
+	}
+
+	go scanPipe(stderrPipe, "stderr")
+	go scanPipe(stdoutPipe, "stdout")
+
+	// Wait for the device name with a timeout.
+	select {
+	case device := <-deviceCh:
+		if device == "" {
+			t.logDebug("Empty device from tun2socks output, trying ifconfig")
+			device, err = t.discoverUtunFromIfconfig()
+			if err != nil {
+				_ = cmd.Process.Kill()
+				return fmt.Errorf("failed to discover utun device: %w", err)
+			}
+		}
+		t.tunDevice = device
+	case <-time.After(10 * time.Second):
+		// Timeout: try ifconfig fallback.
+		t.logDebug("Timeout waiting for tun2socks device name, trying ifconfig")
+		device, err := t.discoverUtunFromIfconfig()
+		if err != nil {
+			_ = cmd.Process.Kill()
+			return fmt.Errorf("tun2socks did not report device name within timeout: %w", err)
+		}
+		t.tunDevice = device
+	}
+
+	t.logDebug("tun2socks started (pid=%d, device=%s)", cmd.Process.Pid, t.tunDevice)
+
+	// Monitor tun2socks in the background.
+	go t.monitorTun2Socks(stderrLines)
+
+	return nil
+}
+
+// discoverUtunFromIfconfig runs ifconfig and looks for a utun device. This is
+// used as a fallback when we cannot parse the device name from tun2socks output.
+func (t *TunManager) discoverUtunFromIfconfig() (string, error) {
+	out, err := exec.Command("ifconfig").Output()
+	if err != nil {
+		return "", fmt.Errorf("ifconfig failed: %w", err)
+	}
+
+	// Look for utun interfaces. We scan for lines starting with "utunN:"
+	// and return the highest-numbered one (most recently created).
+	ifPattern := regexp.MustCompile(`^(utun\d+):`)
+	var lastDevice string
+	for _, line := range strings.Split(string(out), "\n") {
+		if m := ifPattern.FindStringSubmatch(line); m != nil {
+			lastDevice = m[1]
+		}
+	}
+
+	if lastDevice == "" {
+		return "", fmt.Errorf("no utun device found in ifconfig output")
+	}
+
+	return lastDevice, nil
+}
+
+// monitorTun2Socks watches the tun2socks process and logs if it exits unexpectedly.
+func (t *TunManager) monitorTun2Socks(stderrLines <-chan string) {
+	if t.tun2socksCmd == nil || t.tun2socksCmd.Process == nil {
+		return
+	}
+
+	// Drain any remaining stderr lines.
+	go func() {
+		for range stderrLines {
+			// Already logged in the scanner goroutine when debug is on.
+		}
+	}()
+
+	err := t.tun2socksCmd.Wait()
+
+	select {
+	case <-t.done:
+		// Expected shutdown.
+		t.logDebug("tun2socks exited (expected shutdown)")
+	default:
+		// Unexpected exit.
+		fmt.Fprintf(os.Stderr, "[greywall:tun] ERROR: tun2socks exited unexpectedly: %v\n", err)
+	}
+}
+
+// stopTun2Socks sends SIGTERM to the tun2socks process and waits for it to exit.
+// If it does not exit within the grace period, SIGKILL is sent.
+func (t *TunManager) stopTun2Socks() error {
+	if t.tun2socksCmd == nil || t.tun2socksCmd.Process == nil {
+		return nil
+	}
+
+	t.logDebug("Stopping tun2socks (pid=%d)", t.tun2socksCmd.Process.Pid)
+
+	// Send SIGTERM.
+	if err := t.tun2socksCmd.Process.Signal(os.Interrupt); err != nil {
+		// Process may have already exited.
+		t.logDebug("SIGTERM failed (process may have exited): %v", err)
+		t.tun2socksCmd = nil
+		return nil
+	}
+
+	// Wait for exit with a timeout.
+	exited := make(chan error, 1)
+	go func() {
+		// Wait may have already been called by the monitor goroutine,
+		// in which case this will return immediately.
+		exited <- t.tun2socksCmd.Wait()
+	}()
+
+	select {
+	case err := <-exited:
+		if err != nil {
+			t.logDebug("tun2socks exited with: %v", err)
+		}
+	case <-time.After(tun2socksStopGracePeriod):
+		t.logDebug("tun2socks did not exit after SIGTERM, sending SIGKILL")
+		_ = t.tun2socksCmd.Process.Kill()
+	}
+
+	t.tun2socksCmd = nil
+	return nil
+}
+
+// configureInterface sets up the utun interface with a point-to-point IP address.
+func (t *TunManager) configureInterface() error {
+	t.logDebug("Configuring interface %s with IP %s", t.tunDevice, tunIP)
+
+	//nolint:gosec // tunDevice and tunIP are controlled internal values
+	cmd := exec.Command("ifconfig", t.tunDevice, tunIP, tunIP, "up")
+	if output, err := cmd.CombinedOutput(); err != nil {
+		return fmt.Errorf("ifconfig %s failed: %w (output: %s)", t.tunDevice, err, string(output))
+	}
+	return nil
+}
+
+// addLoopbackAlias adds an alias IP on lo0 for the DNS relay.
+func (t *TunManager) addLoopbackAlias() error {
+	t.logDebug("Adding loopback alias %s on lo0", dnsRelayIP)
+
+	cmd := exec.Command("ifconfig", "lo0", "alias", dnsRelayIP, "up")
+	if output, err := cmd.CombinedOutput(); err != nil {
+		return fmt.Errorf("ifconfig lo0 alias failed: %w (output: %s)", err, string(output))
+	}
+	return nil
+}
+
+// removeLoopbackAlias removes the DNS relay alias from lo0.
+func (t *TunManager) removeLoopbackAlias() error {
+	t.logDebug("Removing loopback alias %s from lo0", dnsRelayIP)
+
+	cmd := exec.Command("ifconfig", "lo0", "-alias", dnsRelayIP)
+	if output, err := cmd.CombinedOutput(); err != nil {
+		return fmt.Errorf("ifconfig lo0 -alias failed: %w (output: %s)", err, string(output))
+	}
+	return nil
+}
+
+// ensureAnchorInPFConf checks whether the pf anchor reference exists in
+// /etc/pf.conf. If not, it inserts the anchor lines at the correct positions
+// (pf requires strict ordering: rdr-anchor before anchor, both before load anchor)
+// and reloads the main ruleset.
+func (t *TunManager) ensureAnchorInPFConf() error {
+	const pfConfPath = "/etc/pf.conf"
+	anchorLine := fmt.Sprintf(`anchor "%s"`, t.pfAnchor)
+	rdrAnchorLine := fmt.Sprintf(`rdr-anchor "%s"`, t.pfAnchor)
+
+	data, err := os.ReadFile(pfConfPath)
+	if err != nil {
+		return fmt.Errorf("failed to read %s: %w", pfConfPath, err)
+	}
+
+	lines := strings.Split(string(data), "\n")
+
+	// Line-level presence check avoids substring false positives
+	// (e.g. 'anchor "X"' matching inside 'rdr-anchor "X"').
+	hasAnchor := false
+	hasRdrAnchor := false
+	lastRdrIdx := -1
+	lastAnchorIdx := -1
+
+	for i, line := range lines {
+		trimmed := strings.TrimSpace(line)
+		if trimmed == rdrAnchorLine {
+			hasRdrAnchor = true
+		}
+		if trimmed == anchorLine {
+			hasAnchor = true
+		}
+		if strings.HasPrefix(trimmed, "rdr-anchor ") {
+			lastRdrIdx = i
+		}
+		// Standalone "anchor" lines — not rdr-anchor, nat-anchor, etc.
+		if strings.HasPrefix(trimmed, "anchor ") {
+			lastAnchorIdx = i
+		}
+	}
+
+	if hasAnchor && hasRdrAnchor {
+		t.logDebug("pf anchor already present in %s", pfConfPath)
+		return nil
+	}
+
+	t.logDebug("Adding pf anchor to %s", pfConfPath)
+
+	// Insert at the correct positions. Process in reverse index order
+	// so earlier insertions don't shift later indices.
+	var result []string
+	for i, line := range lines {
+		result = append(result, line)
+		if !hasRdrAnchor && i == lastRdrIdx {
+			result = append(result, rdrAnchorLine)
+		}
+		if !hasAnchor && i == lastAnchorIdx {
+			result = append(result, anchorLine)
+		}
+	}
+
+	// Fallback: if no existing rdr-anchor/anchor found, append at end.
+	if !hasRdrAnchor && lastRdrIdx == -1 {
+		result = append(result, rdrAnchorLine)
+	}
+	if !hasAnchor && lastAnchorIdx == -1 {
+		result = append(result, anchorLine)
+	}
+
+	newContent := strings.Join(result, "\n")
+
+	//nolint:gosec // pf.conf must be writable by root; the daemon runs as root
+	if err := os.WriteFile(pfConfPath, []byte(newContent), 0o644); err != nil {
+		return fmt.Errorf("failed to write %s: %w", pfConfPath, err)
+	}
+
+	// Reload the main pf.conf so the anchor reference is recognized.
+	//nolint:gosec // pfConfPath is a constant
+	reloadCmd := exec.Command("pfctl", "-f", pfConfPath)
+	if output, err := reloadCmd.CombinedOutput(); err != nil {
+		return fmt.Errorf("pfctl reload failed: %w (output: %s)", err, string(output))
+	}
+
+	t.logDebug("pf anchor added and pf.conf reloaded")
+	return nil
+}
+
+// enablePF enables the pf firewall if it is not already active.
+func (t *TunManager) enablePF() error {
+	// Check current pf status.
+	out, err := exec.Command("pfctl", "-s", "info").CombinedOutput()
+	if err == nil && strings.Contains(string(out), "Status: Enabled") {
+		t.logDebug("pf is already enabled")
+		return nil
+	}
+
+	t.logDebug("Enabling pf")
+	cmd := exec.Command("pfctl", "-e")
+	if output, err := cmd.CombinedOutput(); err != nil {
+		return fmt.Errorf("pfctl -e failed: %w (output: %s)", err, string(output))
+	}
+	return nil
+}
+
+// unloadPFRulesLocked flushes all rules from the pf anchor. Must be called
+// with t.mu held.
+func (t *TunManager) unloadPFRulesLocked() error {
+	t.logDebug("Flushing pf anchor %s", t.pfAnchor)
+
+	//nolint:gosec // pfAnchor is a controlled internal constant
+	cmd := exec.Command("pfctl", "-a", t.pfAnchor, "-F", "all")
+	if output, err := cmd.CombinedOutput(); err != nil {
+		return fmt.Errorf("pfctl flush anchor failed: %w (output: %s)", err, string(output))
+	}
+	return nil
+}
+
+// removeAnchorFromPFConf removes greywall anchor lines from /etc/pf.conf.
+// Called during uninstall to clean up.
+func removeAnchorFromPFConf(debug bool) error {
+	const pfConfPath = "/etc/pf.conf"
+	anchorLine := fmt.Sprintf(`anchor "%s"`, pfAnchorName)
+	rdrAnchorLine := fmt.Sprintf(`rdr-anchor "%s"`, pfAnchorName)
+
+	data, err := os.ReadFile(pfConfPath)
+	if err != nil {
+		return fmt.Errorf("failed to read %s: %w", pfConfPath, err)
+	}
+
+	lines := strings.Split(string(data), "\n")
+	var filtered []string
+	removed := 0
+	for _, line := range lines {
+		trimmed := strings.TrimSpace(line)
+		if trimmed == anchorLine || trimmed == rdrAnchorLine {
+			removed++
+			continue
+		}
+		filtered = append(filtered, line)
+	}
+
+	if removed == 0 {
+		logDebug(debug, "No pf anchor lines to remove from %s", pfConfPath)
+		return nil
+	}
+
+	//nolint:gosec // pf.conf must be writable by root; the daemon runs as root
+	if err := os.WriteFile(pfConfPath, []byte(strings.Join(filtered, "\n")), 0o644); err != nil {
+		return fmt.Errorf("failed to write %s: %w", pfConfPath, err)
+	}
+
+	logDebug(debug, "Removed %d pf anchor lines from %s", removed, pfConfPath)
+	return nil
+}
+
+// logDebug writes a debug message to stderr with the [greywall:tun] prefix.
+func (t *TunManager) logDebug(format string, args ...interface{}) {
+	if t.debug {
+		fmt.Fprintf(os.Stderr, "[greywall:tun] "+format+"\n", args...)
+	}
+}

internal/daemon/tun_stub.go

@@ -0,0 +1,38 @@
+//go:build !darwin
+
+package daemon
+
+import "fmt"
+
+// TunManager is a stub for non-macOS platforms.
+type TunManager struct{}
+
+// NewTunManager returns an error on non-macOS platforms.
+func NewTunManager(tun2socksPath string, proxyURL string, debug bool) *TunManager {
+	return &TunManager{}
+}
+
+// Start returns an error on non-macOS platforms.
+func (t *TunManager) Start() error {
+	return fmt.Errorf("tun manager is only available on macOS")
+}
+
+// Stop returns an error on non-macOS platforms.
+func (t *TunManager) Stop() error {
+	return fmt.Errorf("tun manager is only available on macOS")
+}
+
+// TunDevice returns an empty string on non-macOS platforms.
+func (t *TunManager) TunDevice() string {
+	return ""
+}
+
+// LoadPFRules returns an error on non-macOS platforms.
+func (t *TunManager) LoadPFRules(sandboxUser string) error {
+	return fmt.Errorf("pf rules are only available on macOS")
+}
+
+// UnloadPFRules returns an error on non-macOS platforms.
+func (t *TunManager) UnloadPFRules() error {
+	return fmt.Errorf("pf rules are only available on macOS")
+}

internal/sandbox/benchmark_test.go

@@ -333,7 +333,7 @@ func execBenchCommand(b *testing.B, command string, workDir string) {
 		shell = "/bin/bash"
 	}
 
-	cmd := exec.CommandContext(ctx, shell, "-c", command)
+	cmd := exec.CommandContext(ctx, shell, "-c", command) //nolint:gosec // test helper running shell commands
 	cmd.Dir = workDir
 	cmd.Stdout = &bytes.Buffer{}
 	cmd.Stderr = &bytes.Buffer{}

internal/sandbox/integration_test.go

@@ -245,7 +245,7 @@ func executeShellCommandWithTimeout(t *testing.T, command string, workDir string
 		shell = "/bin/bash"
 	}
 
-	cmd := exec.CommandContext(ctx, shell, "-c", command)
+	cmd := exec.CommandContext(ctx, shell, "-c", command) //nolint:gosec // test helper running shell commands
 	cmd.Dir = workDir
 
 	var stdout, stderr bytes.Buffer

internal/sandbox/learning.go

@@ -426,8 +426,8 @@ func buildTemplate(cmdName string, allowRead, allowWrite []string) string {
 	data, _ := json.MarshalIndent(cfg, "", "  ")
 
 	var sb strings.Builder
-	sb.WriteString(fmt.Sprintf("// Learned template for %q\n", cmdName))
+	fmt.Fprintf(&sb, "// Learned template for %q\n", cmdName)
-	sb.WriteString(fmt.Sprintf("// Generated by: greywall --learning -- %s\n", cmdName))
+	fmt.Fprintf(&sb, "// Generated by: greywall --learning -- %s\n", cmdName)
 	sb.WriteString("// Review and adjust paths as needed\n")
 	sb.Write(data)
 	sb.WriteString("\n")

internal/sandbox/linux_stub.go

@@ -64,12 +64,12 @@ func (b *ReverseBridge) Cleanup() {}
 
 // WrapCommandLinux returns an error on non-Linux platforms.
 func WrapCommandLinux(cfg *config.Config, command string, proxyBridge *ProxyBridge, dnsBridge *DnsBridge, reverseBridge *ReverseBridge, tun2socksPath string, debug bool) (string, error) {
-	return "", fmt.Errorf("Linux sandbox not available on this platform")
+	return "", fmt.Errorf("linux sandbox not available on this platform")
 }
 
 // WrapCommandLinuxWithOptions returns an error on non-Linux platforms.
 func WrapCommandLinuxWithOptions(cfg *config.Config, command string, proxyBridge *ProxyBridge, dnsBridge *DnsBridge, reverseBridge *ReverseBridge, tun2socksPath string, opts LinuxSandboxOptions) (string, error) {
-	return "", fmt.Errorf("Linux sandbox not available on this platform")
+	return "", fmt.Errorf("linux sandbox not available on this platform")
 }
 
 // StartLinuxMonitor returns nil on non-Linux platforms.

internal/sandbox/macos.go

@@ -45,6 +45,8 @@ type MacOSSandboxParams struct {
 	AllowPty                bool
 	AllowGitConfig          bool
 	Shell                   string
+	DaemonMode              bool   // When true, pf handles network routing; Seatbelt allows network-outbound
+	DaemonSocketPath        string // Daemon socket to deny access to from sandboxed process
 }
 
 // GlobToRegex converts a glob pattern to a regex for macOS sandbox profiles.
@@ -422,8 +424,8 @@ func GenerateSandboxProfile(params MacOSSandboxParams) string {
 
 	// Header
 	profile.WriteString("(version 1)\n")
-	profile.WriteString(fmt.Sprintf("(deny default (with message %q))\n\n", logTag))
+	fmt.Fprintf(&profile, "(deny default (with message %q))\n\n", logTag)
-	profile.WriteString(fmt.Sprintf("; LogTag: %s\n\n", logTag))
+	fmt.Fprintf(&profile, "; LogTag: %s\n\n", logTag)
 
 	// Essential permissions - based on Chrome sandbox policy
 	profile.WriteString(`; Essential permissions - based on Chrome sandbox policy
@@ -566,9 +568,27 @@ func GenerateSandboxProfile(params MacOSSandboxParams) string {
 
 	// Network rules
 	profile.WriteString("; Network\n")
-	if !params.NeedsNetworkRestriction {
+	switch {
+	case params.DaemonMode:
+		// In daemon mode, pf handles network routing: all traffic from the
+		// _greywall user is routed through utun → tun2socks → proxy.
+		// Seatbelt must allow network-outbound so packets reach pf.
+		// The proxy allowlist is enforced by the external SOCKS5 proxy.
+		profile.WriteString("(allow network-outbound)\n")
+		// Allow local binding for servers if configured.
+		if params.AllowLocalBinding {
+			profile.WriteString(`(allow network-bind (local ip "localhost:*"))
+(allow network-inbound (local ip "localhost:*"))
+`)
+		}
+		// Explicitly deny access to the daemon socket to prevent the
+		// sandboxed process from manipulating daemon sessions.
+		if params.DaemonSocketPath != "" {
+			fmt.Fprintf(&profile, "(deny network-outbound (remote unix-socket (path-literal %s)))\n", escapePath(params.DaemonSocketPath))
+		}
+	case !params.NeedsNetworkRestriction:
 		profile.WriteString("(allow network*)\n")
-	} else {
+	default:
 		if params.AllowLocalBinding {
 			// Allow binding and inbound connections on localhost (for servers)
 			profile.WriteString(`(allow network-bind (local ip "localhost:*"))
@@ -586,14 +606,13 @@ func GenerateSandboxProfile(params MacOSSandboxParams) string {
 		} else if len(params.AllowUnixSockets) > 0 {
 			for _, socketPath := range params.AllowUnixSockets {
 				normalized := NormalizePath(socketPath)
-				profile.WriteString(fmt.Sprintf("(allow network* (subpath %s))\n", escapePath(normalized)))
+				fmt.Fprintf(&profile, "(allow network* (subpath %s))\n", escapePath(normalized))
 			}
 		}
 
 		// Allow outbound to the external proxy host:port
 		if params.ProxyHost != "" && params.ProxyPort != "" {
-			profile.WriteString(fmt.Sprintf(`(allow network-outbound (remote ip "%s:%s"))
+			fmt.Fprintf(&profile, "(allow network-outbound (remote ip \"%s:%s\"))\n", params.ProxyHost, params.ProxyPort)
-`, params.ProxyHost, params.ProxyPort))
 		}
 	}
 	profile.WriteString("\n")
@@ -631,7 +650,9 @@ func GenerateSandboxProfile(params MacOSSandboxParams) string {
 }
 
 // WrapCommandMacOS wraps a command with macOS sandbox restrictions.
-func WrapCommandMacOS(cfg *config.Config, command string, exposedPorts []int, debug bool) (string, error) {
+// When daemonSession is non-nil, the command runs as the _greywall user
+// with network-outbound allowed (pf routes traffic through utun → proxy).
+func WrapCommandMacOS(cfg *config.Config, command string, exposedPorts []int, daemonSession *DaemonSession, debug bool) (string, error) {
 	cwd, _ := os.Getwd()
 
 	// Build allow paths: default + configured
@@ -657,9 +678,13 @@ func WrapCommandMacOS(cfg *config.Config, command string, exposedPorts []int, de
 		}
 	}
 
+	// Determine if we're using daemon-mode (transparent proxying via pf + utun)
+	daemonMode := daemonSession != nil
+
 	// Restrict network unless proxy is configured to an external host
 	// If no proxy: block all outbound. If proxy: allow outbound only to proxy.
-	needsNetworkRestriction := true
+	// In daemon mode, network restriction is handled by pf, not Seatbelt.
+	needsNetworkRestriction := !daemonMode
 
 	params := MacOSSandboxParams{
 		Command:                 command,
@@ -679,6 +704,8 @@ func WrapCommandMacOS(cfg *config.Config, command string, exposedPorts []int, de
 		WriteDenyPaths:          cfg.Filesystem.DenyWrite,
 		AllowPty:                cfg.AllowPty,
 		AllowGitConfig:          cfg.Filesystem.AllowGitConfig,
+		DaemonMode:              daemonMode,
+		DaemonSocketPath:        "/var/run/greywall.sock",
 	}
 
 	if debug && len(exposedPorts) > 0 {
@@ -687,6 +714,10 @@ func WrapCommandMacOS(cfg *config.Config, command string, exposedPorts []int, de
 	if debug && allowLocalBinding && !allowLocalOutbound {
 		fmt.Fprintf(os.Stderr, "[greywall:macos] Blocking localhost outbound (AllowLocalOutbound=false)\n")
 	}
+	if debug && daemonMode {
+		fmt.Fprintf(os.Stderr, "[greywall:macos] Daemon mode: transparent proxying via pf + utun (group=%s, device=%s)\n",
+			daemonSession.SandboxGroup, daemonSession.TunDevice)
+	}
 
 	profile := GenerateSandboxProfile(params)
 
@@ -700,14 +731,23 @@ func WrapCommandMacOS(cfg *config.Config, command string, exposedPorts []int, de
 		return "", fmt.Errorf("shell %q not found: %w", shell, err)
 	}
 
-	proxyEnvs := GenerateProxyEnvVars(cfg.Network.ProxyURL)
-
-	// Build the command
-	// env VAR1=val1 VAR2=val2 sandbox-exec -p 'profile' shell -c 'command'
 	var parts []string
-	parts = append(parts, "env")
+
-	parts = append(parts, proxyEnvs...)
+	if daemonMode {
-	parts = append(parts, "sandbox-exec", "-p", profile, shellPath, "-c", command)
+		// In daemon mode: run as the real user but with EGID=_greywall via sudo.
+		// pf routes all traffic from group _greywall through utun → tun2socks → proxy.
+		// Using -u #<uid> preserves the user's identity (home dir, SSH keys, etc.)
+		// while -g _greywall sets the effective GID for pf matching.
+		uid := fmt.Sprintf("#%d", os.Getuid())
+		parts = append(parts, "sudo", "-u", uid, "-g", daemonSession.SandboxGroup,
+			"sandbox-exec", "-p", profile, shellPath, "-c", command)
+	} else {
+		// Non-daemon mode: use proxy env vars for best-effort proxying.
+		proxyEnvs := GenerateProxyEnvVars(cfg.Network.ProxyURL)
+		parts = append(parts, "env")
+		parts = append(parts, proxyEnvs...)
+		parts = append(parts, "sandbox-exec", "-p", profile, shellPath, "-c", command)
+	}
 
 	return ShellQuote(parts), nil
 }

internal/sandbox/manager.go

@@ -5,9 +5,20 @@ import (
 	"os"
 
 	"gitea.app.monadical.io/monadical/greywall/internal/config"
+	"gitea.app.monadical.io/monadical/greywall/internal/daemon"
 	"gitea.app.monadical.io/monadical/greywall/internal/platform"
 )
 
+// DaemonSession holds the state from an active daemon session on macOS.
+// When a daemon session is active, traffic is routed through pf + utun
+// instead of using env-var proxy settings.
+type DaemonSession struct {
+	SessionID    string
+	TunDevice    string
+	SandboxUser  string
+	SandboxGroup string
+}
+
 // Manager handles sandbox initialization and command wrapping.
 type Manager struct {
 	config        *config.Config
@@ -22,6 +33,9 @@ type Manager struct {
 	learning      bool   // learning mode: permissive sandbox with strace
 	straceLogPath string // host-side temp file for strace output
 	commandName   string // name of the command being learned
+	// macOS daemon session fields
+	daemonClient  *daemon.Client
+	daemonSession *DaemonSession
 }
 
 // NewManager creates a new sandbox manager.
@@ -63,11 +77,36 @@ func (m *Manager) Initialize() error {
 		return fmt.Errorf("sandbox is not supported on platform: %s", platform.Detect())
 	}
 
+	// On macOS, the daemon is required for transparent proxying.
+	// Without it, env-var proxying is unreliable (only works for tools that
+	// honor HTTP_PROXY) and gives users a false sense of security.
+	if platform.Detect() == platform.MacOS && m.config.Network.ProxyURL != "" {
+		client := daemon.NewClient(daemon.DefaultSocketPath, m.debug)
+		if !client.IsRunning() {
+			return fmt.Errorf("greywall daemon is not running (required for macOS network sandboxing)\n\n" +
+				"  Install and start:  sudo greywall daemon install\n" +
+				"  Check status:       greywall daemon status")
+		}
+		m.logDebug("Daemon is running, requesting session")
+		resp, err := client.CreateSession(m.config.Network.ProxyURL, m.config.Network.DnsAddr)
+		if err != nil {
+			return fmt.Errorf("failed to create daemon session: %w", err)
+		}
+		m.daemonClient = client
+		m.daemonSession = &DaemonSession{
+			SessionID:    resp.SessionID,
+			TunDevice:    resp.TunDevice,
+			SandboxUser:  resp.SandboxUser,
+			SandboxGroup: resp.SandboxGroup,
+		}
+		m.logDebug("Daemon session created: id=%s device=%s user=%s group=%s", resp.SessionID, resp.TunDevice, resp.SandboxUser, resp.SandboxGroup)
+	}
+
 	// On Linux, set up proxy bridge and tun2socks if proxy is configured
 	if platform.Detect() == platform.Linux {
 		if m.config.Network.ProxyURL != "" {
 			// Extract embedded tun2socks binary
-			tun2socksPath, err := extractTun2Socks()
+			tun2socksPath, err := ExtractTun2Socks()
 			if err != nil {
 				m.logDebug("Failed to extract tun2socks: %v (will fall back to env-var proxying)", err)
 			} else {
@@ -148,7 +187,7 @@ func (m *Manager) WrapCommand(command string) (string, error) {
 	plat := platform.Detect()
 	switch plat {
 	case platform.MacOS:
-		return WrapCommandMacOS(m.config, command, m.exposedPorts, m.debug)
+		return WrapCommandMacOS(m.config, command, m.exposedPorts, m.daemonSession, m.debug)
 	case platform.Linux:
 		if m.learning {
 			return m.wrapCommandLearning(command)
@@ -201,6 +240,16 @@ func (m *Manager) GenerateLearnedTemplate(cmdName string) (string, error) {
 
 // Cleanup stops the proxies and cleans up resources.
 func (m *Manager) Cleanup() {
+	// Destroy macOS daemon session if active.
+	if m.daemonClient != nil && m.daemonSession != nil {
+		m.logDebug("Destroying daemon session %s", m.daemonSession.SessionID)
+		if err := m.daemonClient.DestroySession(m.daemonSession.SessionID); err != nil {
+			m.logDebug("Warning: failed to destroy daemon session: %v", err)
+		}
+		m.daemonSession = nil
+		m.daemonClient = nil
+	}
+
 	if m.reverseBridge != nil {
 		m.reverseBridge.Cleanup()
 	}

internal/sandbox/monitor.go

@@ -66,7 +66,7 @@ func (m *LogMonitor) Start() error {
 		for scanner.Scan() {
 			line := scanner.Text()
 			if violation := parseViolation(line); violation != "" {
-				fmt.Fprintf(os.Stderr, "%s\n", violation)
+				fmt.Fprintf(os.Stderr, "%s\n", violation) //nolint:gosec // logging to stderr, not web output
 			}
 		}
 	}()

internal/sandbox/tun2socks_embed.go

@@ -13,9 +13,9 @@ import (
 //go:embed bin/tun2socks-linux-*
 var tun2socksFS embed.FS
 
-// extractTun2Socks writes the embedded tun2socks binary to a temp file and returns its path.
+// ExtractTun2Socks writes the embedded tun2socks binary to a temp file and returns its path.
 // The caller is responsible for removing the file when done.
-func extractTun2Socks() (string, error) {
+func ExtractTun2Socks() (string, error) {
 	var arch string
 	switch runtime.GOARCH {
 	case "amd64":

internal/sandbox/tun2socks_embed_darwin.go

@@ -0,0 +1,53 @@
+//go:build darwin
+
+package sandbox
+
+import (
+	"embed"
+	"fmt"
+	"io/fs"
+	"os"
+	"runtime"
+)
+
+//go:embed bin/tun2socks-darwin-*
+var tun2socksFS embed.FS
+
+// ExtractTun2Socks writes the embedded tun2socks binary to a temp file and returns its path.
+// The caller is responsible for removing the file when done.
+func ExtractTun2Socks() (string, error) {
+	var arch string
+	switch runtime.GOARCH {
+	case "amd64":
+		arch = "amd64"
+	case "arm64":
+		arch = "arm64"
+	default:
+		return "", fmt.Errorf("tun2socks: unsupported architecture %s", runtime.GOARCH)
+	}
+
+	name := fmt.Sprintf("bin/tun2socks-darwin-%s", arch)
+	data, err := fs.ReadFile(tun2socksFS, name)
+	if err != nil {
+		return "", fmt.Errorf("tun2socks: embedded binary not found for %s: %w", arch, err)
+	}
+
+	tmpFile, err := os.CreateTemp("", "greywall-tun2socks-*")
+	if err != nil {
+		return "", fmt.Errorf("tun2socks: failed to create temp file: %w", err)
+	}
+
+	if _, err := tmpFile.Write(data); err != nil {
+		_ = tmpFile.Close()
+		_ = os.Remove(tmpFile.Name()) //nolint:gosec // path from os.CreateTemp, not user input
+		return "", fmt.Errorf("tun2socks: failed to write binary: %w", err)
+	}
+	_ = tmpFile.Close()
+
+	if err := os.Chmod(tmpFile.Name(), 0o755); err != nil { //nolint:gosec // executable binary needs execute permission
+		_ = os.Remove(tmpFile.Name()) //nolint:gosec // path from os.CreateTemp, not user input
+		return "", fmt.Errorf("tun2socks: failed to make executable: %w", err)
+	}
+
+	return tmpFile.Name(), nil
+}

internal/sandbox/tun2socks_embed_stub.go

@@ -1,10 +1,10 @@
-//go:build !linux
+//go:build !linux && !darwin
 
 package sandbox
 
 import "fmt"
 
-// extractTun2Socks is not available on non-Linux platforms.
+// ExtractTun2Socks is not available on unsupported platforms.
-func extractTun2Socks() (string, error) {
+func ExtractTun2Socks() (string, error) {
-	return "", fmt.Errorf("tun2socks is only available on Linux")
+	return "", fmt.Errorf("tun2socks is only available on Linux and macOS")
 }