fix(failover): satisfy lint on the manager package

errcheck flagged two side-effect-only m.Plan calls in tests, and unused
flagged close(), which Task 5's probe scheduler wires in.

Assisted-by: Claude:claude-opus-5-5

core/services/failover/manager.go

@@ -575,6 +575,7 @@ func (m *Manager) emitLocked(ev Event) {
 	}
 }
 
+//nolint:unused // wired by the Task 5 probe scheduler's Stop, which owns the manager's lifecycle
 func (m *Manager) close() {
 	m.mu.Lock()
 	defer m.mu.Unlock()

core/services/failover/manager_test.go

@@ -88,7 +88,7 @@ var _ = Describe("Manager", func() {
 	})
 
 	It("fails back only after recovery probes and min_dwell", func() {
-		m.Plan("chain")
+		_, _ = m.Plan("chain")
 		m.ReportFailure("a", errBoom)
 		for i := 0; i < 3; i++ {
 			m.ReportSuccess("a") // a real success counts like a passed inference probe
@@ -158,7 +158,7 @@ var _ = Describe("Manager", func() {
 	})
 
 	It("marks a removed target missing and leaves it out of plans", func() {
-		m.Plan("chain")
+		_, _ = m.Plan("chain")
 		src.Delete("a")
 		m.Sync()
 		st, _ := m.ChainStatus("chain")