diff --git a/daemon.go b/daemon.go
index 1fffeaa..78c1c17 100644
--- a/daemon.go
+++ b/daemon.go
@@ -2,6 +2,8 @@ package main
 
 import (
 	"encoding/json"
+	"fmt"
+	"net"
 	"os"
 	"path/filepath"
 	"sync"
@@ -139,3 +141,220 @@ func (ls *LabelStore) save() error {
 
 	return os.WriteFile(ls.path, data, 0o644)
 }
+
+// Daemon is the long-running vmuxd process. It polls /proc for Claude sessions,
+// maintains the registry, and serves requests over a Unix socket.
+type Daemon struct {
+	registry          *SessionRegistry
+	labels            *LabelStore
+	sockPath          string
+	procDir           string
+	claudeDir         string
+	workspaceResolver func(claudePID int) string // nil = no workspace resolution
+	pollInterval      time.Duration
+	stopCh            chan struct{}
+	listener          net.Listener
+}
+
+// NewDaemon creates a daemon ready to start.
+func NewDaemon(sockPath, procDir, claudeDir string, labels *LabelStore) *Daemon {
+	return &Daemon{
+		registry:     NewRegistry(),
+		labels:       labels,
+		sockPath:     sockPath,
+		procDir:      procDir,
+		claudeDir:    claudeDir,
+		pollInterval: 5 * time.Second,
+		stopCh:       make(chan struct{}),
+	}
+}
+
+// Start runs the daemon: initial scan, then listens on the Unix socket
+// and polls for sessions in the background.
+func (d *Daemon) Start() error {
+	// Synchronous initial scan before accepting connections
+	d.scanOnce(time.Now())
+
+	if err := d.cleanStaleSocket(); err != nil {
+		return fmt.Errorf("clean stale socket: %w", err)
+	}
+
+	ln, err := net.Listen("unix", d.sockPath)
+	if err != nil {
+		return fmt.Errorf("listen %s: %w", d.sockPath, err)
+	}
+	d.listener = ln
+
+	// Poll loop in background
+	go d.pollLoop()
+
+	// Accept loop
+	go d.acceptLoop()
+
+	return nil
+}
+
+// Stop shuts down the daemon gracefully.
+func (d *Daemon) Stop() {
+	select {
+	case <-d.stopCh:
+		return // already stopped
+	default:
+		close(d.stopCh)
+	}
+	if d.listener != nil {
+		d.listener.Close()
+	}
+}
+
+// Wait blocks until the daemon stops.
+func (d *Daemon) Wait() {
+	<-d.stopCh
+}
+
+func (d *Daemon) acceptLoop() {
+	for {
+		conn, err := d.listener.Accept()
+		if err != nil {
+			select {
+			case <-d.stopCh:
+				return
+			default:
+				continue
+			}
+		}
+		go d.handleConnection(conn)
+	}
+}
+
+func (d *Daemon) pollLoop() {
+	ticker := time.NewTicker(d.pollInterval)
+	defer ticker.Stop()
+
+	for {
+		select {
+		case <-d.stopCh:
+			return
+		case t := <-ticker.C:
+			d.scanOnce(t)
+		}
+	}
+}
+
+func (d *Daemon) scanOnce(now time.Time) {
+	procs, err := FindClaudeProcesses(d.procDir)
+	if err != nil {
+		return
+	}
+
+	activeIDs := make(map[string]bool)
+
+	for _, proc := range procs {
+		_, messages, err := FindSessionForProcess(d.claudeDir, proc)
+		if err != nil {
+			continue
+		}
+
+		state := DetectState(messages, now)
+		preview := ExtractPreview(messages)
+
+		var sessionID, gitBranch string
+		for _, msg := range messages {
+			if msg.SessionID != "" {
+				sessionID = msg.SessionID
+			}
+			if msg.GitBranch != "" {
+				gitBranch = msg.GitBranch
+			}
+		}
+
+		if sessionID == "" {
+			continue
+		}
+
+		workspace := ""
+		if d.workspaceResolver != nil {
+			workspace = d.workspaceResolver(proc.PID)
+		}
+
+		label := d.labels.Get(sessionID)
+
+		info := SessionInfo{
+			PID:       proc.PID,
+			SessionID: sessionID,
+			Cwd:       proc.Cwd,
+			GitBranch: gitBranch,
+			State:     state.String(),
+			Preview:   preview,
+			Workspace: workspace,
+			Label:     label,
+		}
+
+		d.registry.Update(info)
+		activeIDs[sessionID] = true
+	}
+
+	d.registry.RemoveStale(activeIDs)
+}
+
+func (d *Daemon) handleConnection(conn net.Conn) {
+	defer conn.Close()
+
+	var req Request
+	if err := json.NewDecoder(conn).Decode(&req); err != nil {
+		writeResponse(conn, Response{Error: "invalid request: " + err.Error()})
+		return
+	}
+
+	switch req.Action {
+	case "list":
+		sessions := d.registry.List()
+		writeResponse(conn, Response{OK: true, Sessions: sessions})
+
+	case "label":
+		var args LabelArgs
+		if err := json.Unmarshal(req.Args, &args); err != nil {
+			writeResponse(conn, Response{Error: "invalid label args: " + err.Error()})
+			return
+		}
+		if err := d.labels.Set(args.SessionID, args.Label); err != nil {
+			writeResponse(conn, Response{Error: "set label: " + err.Error()})
+			return
+		}
+		// Update registry with new label
+		d.registry.mu.Lock()
+		if ts, ok := d.registry.sessions[args.SessionID]; ok {
+			ts.Info.Label = args.Label
+		}
+		d.registry.mu.Unlock()
+		writeResponse(conn, Response{OK: true})
+
+	case "stop":
+		writeResponse(conn, Response{OK: true})
+		d.Stop()
+
+	default:
+		writeResponse(conn, Response{Error: "unknown action: " + req.Action})
+	}
+}
+
+func writeResponse(conn net.Conn, resp Response) {
+	json.NewEncoder(conn).Encode(resp)
+}
+
+// cleanStaleSocket removes a leftover socket file if no process is listening on it.
+func (d *Daemon) cleanStaleSocket() error {
+	if _, err := os.Stat(d.sockPath); os.IsNotExist(err) {
+		return nil
+	}
+
+	// Try connecting to check if another daemon is running
+	conn, err := net.DialTimeout("unix", d.sockPath, 500*time.Millisecond)
+	if err == nil {
+		conn.Close()
+		return fmt.Errorf("another daemon is already listening on %s", d.sockPath)
+	}
+
+	// Stale socket, remove it
+	return os.Remove(d.sockPath)
+}
diff --git a/daemon_test.go b/daemon_test.go
index 0172a3d..757823e 100644
--- a/daemon_test.go
+++ b/daemon_test.go
@@ -1,6 +1,8 @@
 package main
 
 import (
+	"encoding/json"
+	"net"
 	"os"
 	"path/filepath"
 	"testing"
@@ -173,7 +175,151 @@ func TestRegistryUpdateTimestamp(t *testing.T) {
 	}
 }
 
-// Placeholder to verify file exists
-func init() {
-	_ = os.TempDir()
+// sendRequest dials the daemon socket, sends a Request, and decodes the Response.
+func sendRequest(t *testing.T, sockPath string, req Request) Response {
+	t.Helper()
+	conn, err := net.Dial("unix", sockPath)
+	if err != nil {
+		t.Fatalf("dial: %v", err)
+	}
+	defer conn.Close()
+
+	if err := json.NewEncoder(conn).Encode(req); err != nil {
+		t.Fatalf("encode: %v", err)
+	}
+
+	var resp Response
+	if err := json.NewDecoder(conn).Decode(&resp); err != nil {
+		t.Fatalf("decode: %v", err)
+	}
+	return resp
+}
+
+// newTestDaemon creates a daemon using temp dirs (no real /proc or claude dir).
+func newTestDaemon(t *testing.T) *Daemon {
+	t.Helper()
+	dir := t.TempDir()
+	sockPath := filepath.Join(dir, "vmux.sock")
+	procDir := filepath.Join(dir, "proc")   // empty, no processes
+	claudeDir := filepath.Join(dir, "claude")
+	labelsPath := filepath.Join(dir, "labels.json")
+
+	os.MkdirAll(procDir, 0o755)
+	os.MkdirAll(claudeDir, 0o755)
+
+	labels, err := NewLabelStore(labelsPath)
+	if err != nil {
+		t.Fatalf("labels: %v", err)
+	}
+
+	return NewDaemon(sockPath, procDir, claudeDir, labels)
+}
+
+func TestDaemonStartStop(t *testing.T) {
+	d := newTestDaemon(t)
+
+	if err := d.Start(); err != nil {
+		t.Fatalf("start: %v", err)
+	}
+
+	// Send stop via socket
+	resp := sendRequest(t, d.sockPath, Request{Action: "stop"})
+	if !resp.OK {
+		t.Errorf("stop resp.OK = false, error = %q", resp.Error)
+	}
+
+	// Daemon should stop within a short time
+	done := make(chan struct{})
+	go func() {
+		d.Wait()
+		close(done)
+	}()
+
+	select {
+	case <-done:
+		// ok
+	case <-time.After(2 * time.Second):
+		t.Fatal("daemon did not stop within 2s")
+	}
+}
+
+func TestDaemonListOverSocket(t *testing.T) {
+	d := newTestDaemon(t)
+
+	if err := d.Start(); err != nil {
+		t.Fatalf("start: %v", err)
+	}
+	defer d.Stop()
+
+	// Populate registry after Start (initial scan clears unknown sessions)
+	d.registry.Update(SessionInfo{
+		PID:       42,
+		SessionID: "test-sess",
+		State:     "Working",
+		Cwd:       "/tmp/test",
+	})
+
+	resp := sendRequest(t, d.sockPath, Request{Action: "list"})
+	if !resp.OK {
+		t.Fatalf("list resp.OK = false, error = %q", resp.Error)
+	}
+	if len(resp.Sessions) != 1 {
+		t.Fatalf("sessions len = %d, want 1", len(resp.Sessions))
+	}
+	if resp.Sessions[0].SessionID != "test-sess" {
+		t.Errorf("session_id = %q, want %q", resp.Sessions[0].SessionID, "test-sess")
+	}
+}
+
+func TestDaemonLabelOverSocket(t *testing.T) {
+	d := newTestDaemon(t)
+
+	if err := d.Start(); err != nil {
+		t.Fatalf("start: %v", err)
+	}
+	defer d.Stop()
+
+	// Populate registry after Start (initial scan clears unknown sessions)
+	d.registry.Update(SessionInfo{
+		PID:       42,
+		SessionID: "test-sess",
+		State:     "Working",
+		Cwd:       "/tmp/test",
+	})
+
+	// Set label
+	args, _ := json.Marshal(LabelArgs{SessionID: "test-sess", Label: "review MR"})
+	resp := sendRequest(t, d.sockPath, Request{Action: "label", Args: args})
+	if !resp.OK {
+		t.Fatalf("label resp.OK = false, error = %q", resp.Error)
+	}
+
+	// Verify label appears in list
+	resp = sendRequest(t, d.sockPath, Request{Action: "list"})
+	if !resp.OK {
+		t.Fatalf("list resp.OK = false, error = %q", resp.Error)
+	}
+	if len(resp.Sessions) != 1 {
+		t.Fatalf("sessions len = %d, want 1", len(resp.Sessions))
+	}
+	if resp.Sessions[0].Label != "review MR" {
+		t.Errorf("label = %q, want %q", resp.Sessions[0].Label, "review MR")
+	}
+}
+
+func TestDaemonUnknownAction(t *testing.T) {
+	d := newTestDaemon(t)
+
+	if err := d.Start(); err != nil {
+		t.Fatalf("start: %v", err)
+	}
+	defer d.Stop()
+
+	resp := sendRequest(t, d.sockPath, Request{Action: "bogus"})
+	if resp.OK {
+		t.Error("expected OK=false for unknown action")
+	}
+	if resp.Error == "" {
+		t.Error("expected error message for unknown action")
+	}
 }