Say in every declaration the assignment generation it came from, and record every send (hq issue 234)

A declaration newer in sequence than every other named four fewer modules
than the assignments held, a machine applied it, and nothing the mesh kept
said who sent it or from what view. The store now raises an assignment
generation in the same transaction as every assignment change (a trigger,
so a cascade counts too); a send reads it before composing, carries it to
engines that said they read it, marks a gate's put-back, and is recorded
with its sequence, sender, generation and modules. The would-send is
stamped with what was last sent, so nothing reads behind for it; a refusal
is kept on the send it refused and raised as S20 naming the sender; plan
says what the machine was last told.

cmd/mesh-controller/plan.go

@@ -420,7 +420,8 @@ func declarationWith(ctx context.Context, open *stores, node string,
 	out := sendable{Resources: composed.Resources, Adoption: adoption,
 		Received: composed.Received, Mesh: with.Mesh, BusUsers: with.BusUsers,
 		LeftOut: sortedKeysOf(composed.LeftOut), leftOutWhy: composed.LeftOut, withheld: with.Withheld,
-		unbound: with.Unbound, foreseen: composed.Foreseen, unplaced: composed.Unplaced}
+		unbound: with.Unbound, foreseen: composed.Foreseen, unplaced: composed.Unplaced,
+		modules: namedModules(plan, composed.LeftOut)}
 	// And which build of each module it carries, for the send to record (novox/hq issue 259, ADR
 	// 0221). Read only on the send path: a question about what would be sent records nothing.
 	if choosing == Allocating {
@@ -1290,6 +1291,11 @@ func planCommand(ctx context.Context, args []string) error {
 		return nil
 	}
 
+	// What the machine was last told, by whom and from which assignment generation (novox/hq issue 234),
+	// beside what it would be told now. A record that cannot be read is said, not taken for none.
+	if err := writeLastSend(ctx, os.Stdout, open.inventory, args[0]); err != nil {
+		fmt.Printf("what %s was last sent could not be read: %v\n", args[0], err)
+	}
 	// Which modules a push would leave out, and why — said before the plan, since the plan is of
 	// what the machine would be told (novox/hq ADR 0163, rule 6). Judged, never composed: `plan`
 	// without --json allocates nothing.