Fence the two coordinator-side stops nobody had leased

F65, found live on run 20. A plan mismatch asking for a human decision
recorded its observation, then failed to block the task: Store.Append fences
every lifecycle event on a leased task against the current owner and epoch,
and this TaskBlocked carried neither. The task kept implementing while the
contradiction sat durable in the log, and the agent was told its report was
refused. The trajectory gate had the same omission.

The human-decision path already did this correctly and explained why in a
comment. That comment is now a helper all three call.

The tests could not have caught it. planWith never leased its task, so
every plan test ran in a state no agent can be in, which is exactly what
the lease helper's own comment warns against. It leases now, and the
mismatch block test fails without the fence.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01CVbaKucEYBjMqVeUgJUsc1

internal/operations/planprogress_test.go

@@ -28,6 +28,11 @@ func planProject() registry.Project {
 func planWith(t *testing.T, markdown string) (*store.Store, registry.Project, string) {
 	t.Helper()
 	s, id := phaseStore(t)
+	// Leased, because everything these tests drive comes from a live implement
+	// session. Skipping it hid F65: two coordinator-side stops omitted the
+	// fencing fields Store.Append requires on a leased task, and every test
+	// passed because no test ever leased one.
+	lease(t, s, id)
 	project := planProject()
 	if _, err := AdvanceWorkPhase(s, project, id, nil); err != nil {
 		t.Fatal(err)