knowledge-base: retract an accepted record or its clauses on the operator's Approve

The operator prefers removing a wrong decision to stacking a correcting
record on it, and withdraw took only reserved or proposed records. retract
asks the operator through the router like a record that needs the operator,
and changes nothing until the Approve; a retracted record or clause no longer
holds in ask, holds, get, links and progress, history keeps every version, and
the whole-set rules still read a retracted record's links so a retraction alone
raises no finding. withdraw with retraction true takes a waiting one back.

modules/mesh-knowledge/cmd/mesh-knowledge/bus_test.go

@@ -369,6 +369,11 @@ func TestTheKnowledgeBaseOverTheBus(t *testing.T) {
 	if g.Status != StatusProposed || len(g.Clauses) != 2 || g.Clauses[0].Holds != "proposed: not in force" {
 		t.Fatalf("get: %+v", g)
 	}
+	// retract is served, its arguments read as an agent sends them: a proposed record is withdrawn, not retracted.
+	if _, err := b.call(Seat+".retract", map[string]any{"number": 300, "clauses": []int{1}, "why": "never verified"}); err == nil ||
+		!strings.Contains(err.Error(), "withdraw it instead") {
+		t.Fatalf("retract of a proposed record over the bus: %v", err)
+	}
 	var h Historied
 	_ = json.Unmarshal(must(b.call(Seat+".history", map[string]any{"number": 300, "from": 1, "to": 2})), &h)
 	if len(h.Versions) != 2 || len(h.Diff) == 0 {