diff --git a/internal/session/lease.go b/internal/session/lease.go
index 4b57324..7d0257e 100644
--- a/internal/session/lease.go
+++ b/internal/session/lease.go
@@ -2,6 +2,7 @@ package session
 
 import (
 	"encoding/json"
+	"errors"
 	"fmt"
 	"os"
 	"os/user"
@@ -113,3 +114,44 @@ func NewLease(startedAt time.Time, agent, mode string) *Lease {
 		Terminal:        currentTerminal(),
 	}
 }
+
+// IsFresh returns true if the lease's last heartbeat is within threshold
+// of now. A lease with a zero LastHeartbeatAt is treated as stale.
+func IsFresh(l *Lease, now time.Time, threshold time.Duration) bool {
+	if l == nil || l.LastHeartbeatAt.IsZero() {
+		return false
+	}
+	return now.Sub(l.LastHeartbeatAt) <= threshold
+}
+
+// CleanupStaleLease inspects the lease at path:
+//   - missing file: no-op, returns (nil, nil)
+//   - corrupt / unparseable: removes the file, returns (nil, nil)
+//   - stale (heartbeat older than staleAfter): removes the file, returns the parsed lease
+//   - fresh: no-op, returns (nil, nil)
+//
+// An I/O error during removal is returned to the caller along with the
+// parsed lease (if any), so the caller can log it explicitly.
+func CleanupStaleLease(path string, staleAfter time.Duration) (*Lease, error) {
+	data, err := os.ReadFile(path)
+	if errors.Is(err, os.ErrNotExist) {
+		return nil, nil
+	}
+	if err != nil {
+		return nil, err
+	}
+	var l Lease
+	if jsonErr := json.Unmarshal(data, &l); jsonErr != nil {
+		if rmErr := os.Remove(path); rmErr != nil && !errors.Is(rmErr, os.ErrNotExist) {
+			return nil, rmErr
+		}
+		return nil, nil
+	}
+	if IsFresh(&l, time.Now(), staleAfter) {
+		return nil, nil
+	}
+	if rmErr := os.Remove(path); rmErr != nil && !errors.Is(rmErr, os.ErrNotExist) {
+		return &l, rmErr
+	}
+	return &l, nil
+}
diff --git a/internal/session/lease_test.go b/internal/session/lease_test.go
index 8a73ba4..e86927c 100644
--- a/internal/session/lease_test.go
+++ b/internal/session/lease_test.go
@@ -139,3 +139,101 @@ func TestNewLeasePopulatesIdentity(t *testing.T) {
 		t.Errorf("SessionID %q should contain hostname %q", l.SessionID, l.Hostname)
 	}
 }
+
+func TestIsFresh(t *testing.T) {
+	now := time.Date(2026, 4, 21, 14, 30, 22, 0, time.UTC)
+	fresh := &Lease{LastHeartbeatAt: now.Add(-10 * time.Second)}
+	stale := &Lease{LastHeartbeatAt: now.Add(-90 * time.Second)}
+
+	if !IsFresh(fresh, now, 60*time.Second) {
+		t.Error("expected fresh lease to be fresh")
+	}
+	if IsFresh(stale, now, 60*time.Second) {
+		t.Error("expected stale lease to be stale")
+	}
+}
+
+func TestCleanupStaleLeaseRemovesStale(t *testing.T) {
+	dir := t.TempDir()
+	path := filepath.Join(dir, ".ctask", "session.json")
+	os.MkdirAll(filepath.Dir(path), 0755)
+
+	old := time.Now().Add(-5 * time.Minute).UTC().Truncate(time.Second)
+	stale := &Lease{
+		SessionID:       "h-1-x",
+		Hostname:        "h",
+		StartedAt:       old,
+		LastHeartbeatAt: old,
+	}
+	if err := WriteLease(path, stale); err != nil {
+		t.Fatalf("seed WriteLease: %v", err)
+	}
+
+	removed, err := CleanupStaleLease(path, 60*time.Second)
+	if err != nil {
+		t.Fatalf("CleanupStaleLease: %v", err)
+	}
+	if removed == nil {
+		t.Fatal("expected removed lease to be returned")
+	}
+	if removed.Hostname != "h" {
+		t.Errorf("removed lease hostname: got %q", removed.Hostname)
+	}
+	if _, err := os.Stat(path); !errors.Is(err, os.ErrNotExist) {
+		t.Error("lease file should be removed after stale cleanup")
+	}
+}
+
+func TestCleanupStaleLeaseKeepsFresh(t *testing.T) {
+	dir := t.TempDir()
+	path := filepath.Join(dir, ".ctask", "session.json")
+	os.MkdirAll(filepath.Dir(path), 0755)
+
+	now := time.Now().UTC().Truncate(time.Second)
+	fresh := &Lease{Hostname: "h", LastHeartbeatAt: now}
+	if err := WriteLease(path, fresh); err != nil {
+		t.Fatalf("seed WriteLease: %v", err)
+	}
+
+	removed, err := CleanupStaleLease(path, 60*time.Second)
+	if err != nil {
+		t.Fatalf("CleanupStaleLease: %v", err)
+	}
+	if removed != nil {
+		t.Errorf("fresh lease should not be removed, got %+v", removed)
+	}
+	if _, err := os.Stat(path); err != nil {
+		t.Errorf("fresh lease file should still exist: %v", err)
+	}
+}
+
+func TestCleanupStaleLeaseMissingIsNoop(t *testing.T) {
+	dir := t.TempDir()
+	path := filepath.Join(dir, ".ctask", "session.json")
+
+	removed, err := CleanupStaleLease(path, 60*time.Second)
+	if err != nil {
+		t.Fatalf("missing lease should be a no-op, got err=%v", err)
+	}
+	if removed != nil {
+		t.Errorf("missing lease: got %+v, want nil", removed)
+	}
+}
+
+func TestCleanupStaleLeaseCorruptRemoves(t *testing.T) {
+	dir := t.TempDir()
+	path := filepath.Join(dir, ".ctask", "session.json")
+	os.MkdirAll(filepath.Dir(path), 0755)
+	os.WriteFile(path, []byte("not json"), 0644)
+
+	removed, err := CleanupStaleLease(path, 60*time.Second)
+	if err != nil {
+		t.Fatalf("CleanupStaleLease should swallow parse errors: %v", err)
+	}
+	if removed != nil {
+		t.Errorf("corrupt lease should not return a parsed lease, got %+v", removed)
+	}
+	if _, err := os.Stat(path); !errors.Is(err, os.ErrNotExist) {
+		t.Error("corrupt lease file should be removed")
+	}
+}