feat(v0.4): add NewLease and NewSessionID constructors

internal/session/lease.go

@@ -89,3 +89,27 @@ func currentTerminal() string {
 	}
 	return "unknown"
 }
+
+// NewSessionID returns a session identifier in the format
+// "<hostname>-<pid>-<YYYYMMDDHHMMSS>" using the given time in UTC.
+func NewSessionID(hostname string, pid int, t time.Time) string {
+	return fmt.Sprintf("%s-%d-%s", hostname, pid, t.UTC().Format("20060102150405"))
+}
+
+// NewLease constructs a fresh lease for the current process. startedAt is used
+// for both StartedAt and LastHeartbeatAt.
+func NewLease(startedAt time.Time, agent, mode string) *Lease {
+	hostname := currentHostname()
+	pid := os.Getpid()
+	return &Lease{
+		SessionID:       NewSessionID(hostname, pid, startedAt),
+		PID:             pid,
+		Hostname:        hostname,
+		Username:        currentUsername(),
+		Agent:           agent,
+		Mode:            mode,
+		StartedAt:       startedAt.UTC().Truncate(time.Second),
+		LastHeartbeatAt: startedAt.UTC().Truncate(time.Second),
+		Terminal:        currentTerminal(),
+	}
+}

internal/session/lease_test.go

@@ -100,3 +100,42 @@ func TestReadLeaseMissingFileReturnsErrNotExist(t *testing.T) {
 		t.Errorf("expected os.ErrNotExist, got %v", err)
 	}
 }
+
+func TestNewSessionIDFormat(t *testing.T) {
+	now := time.Date(2026, 4, 21, 14, 30, 22, 0, time.UTC)
+	id := NewSessionID("warren-desktop", 12345, now)
+	want := "warren-desktop-12345-20260421143022"
+	if id != want {
+		t.Errorf("NewSessionID = %q, want %q", id, want)
+	}
+}
+
+func TestNewLeasePopulatesIdentity(t *testing.T) {
+	now := time.Date(2026, 4, 21, 14, 30, 22, 0, time.UTC)
+	l := NewLease(now, "claude", "local")
+
+	if l.StartedAt != now {
+		t.Errorf("StartedAt: got %v, want %v", l.StartedAt, now)
+	}
+	if l.LastHeartbeatAt != now {
+		t.Errorf("LastHeartbeatAt should be initialized to StartedAt, got %v", l.LastHeartbeatAt)
+	}
+	if l.Agent != "claude" {
+		t.Errorf("Agent: got %q, want %q", l.Agent, "claude")
+	}
+	if l.Mode != "local" {
+		t.Errorf("Mode: got %q, want %q", l.Mode, "local")
+	}
+	if l.PID != os.Getpid() {
+		t.Errorf("PID: got %d, want %d", l.PID, os.Getpid())
+	}
+	if l.Hostname == "" {
+		t.Error("Hostname should not be empty")
+	}
+	if l.Username == "" {
+		t.Error("Username should not be empty")
+	}
+	if !strings.Contains(l.SessionID, l.Hostname) {
+		t.Errorf("SessionID %q should contain hostname %q", l.SessionID, l.Hostname)
+	}
+}