Ask an acknowledgement apart from an approval, change every kept ask by compare-and-set, and rehearse rather than drill (hq ADR 0259, review M1/L2/L3/L7)

- M1: a condition offering both kinds of answer is asked twice: its authorising answers about the
  condition, its acknowledging ones (Silence) apart, so an answer from a channel that only acknowledges
  never ends an approval.
- L2: the asked store creates once and changes only over the revision it read, deciding again on what it
  reads; a stale cancel no longer writes over an act.
- L3: every ask is kept before it is published, one whose publishing failed is marked unsent and asked
  again, and a cancel is kept before it is said. The terminal's test question is now `rehearse`, so it is
  not called what the glossary calls a drill; its two answers are both approve-level.
- L7: two deliveries of one warrant to two controllers at once act exactly once, on a real bus.
- Re-vendored onto mesh-sdk 76902998 (canonical digests): an option binds an asks.Act with each argument
  as arg.<name>.
- The lab's bus fixture composes verified-sender only where the lab says its machine is root-free
  (MESH_LAB_ASKS_ROOT_FREE=true).

cmd/mesh-controller/main.go

@@ -78,8 +78,8 @@ func run() error {
 		return rotateCommand(ctx, args[1:])
 	case "ask":
 		return askCommand(ctx, args[1:])
-	case "drill":
-		return drillCommand(ctx, args[1:])
+	case "rehearse":
+		return rehearseCommand(ctx, args[1:])
 	case "builds":
 		return buildsCommand(ctx, args[1:])
 	// The build queue, controlled by hand (novox/hq ADR 0219).