Keep a group member of the other kind's batch from being overtaken (hq issue 525)

A merge's group member counted as merged when its merge waited in any batch,
but kinds never share a batch: the later member got a batch of its own, cut
at once, and walked before the earlier member's batch was cut, breaking the
group's order (ADR 0276 §5). Only a member kept in a batch of the merge's own
kind counts as merged now; one kept in the other kind's keeps the merge
waiting, and its batch names that member, so the two are cut in the order
their windows close (review of #250).

cmd/mesh-controller/batches.go

@@ -179,7 +179,8 @@ func (f following) hearMerge(ctx context.Context, m link.SourceMoved, now time.T
 		return nil
 	}
 	// **Its delivery group's word, before the plans are held** (ADR 0306 decision 2): a slow answer holds up no walk.
-	waits, err := groupWait(ctx, inv, m, deliverySeatHeld(entries))
+	own := ownPath(touches)
+	waits, err := groupWait(ctx, inv, m, deliverySeatHeld(entries), own)
 	if err != nil {
 		return notNow(err)
 	}
@@ -208,7 +209,6 @@ func (f following) hearMerge(ctx context.Context, m link.SourceMoved, now time.T
 	// **A merge on the controller's own path never shares a batch with one that waits for the delivery's
 	// word** (decided during the build, 2026-10-10): batched together, the catalogue's deliveries would start
 	// with the controller's and skip their turn. Each kind has a batch of its own.
-	own := ownPath(touches)
 	if p, ok, err := answeredByALaterMerge(ctx, inv, heard, touches, own, deliverySeatHeld(entries)); err != nil {
 		return notNow(err)
 	} else if ok {