Say each machine's last send in status and node show, and as fields in status --json (novox/hq issue 485)

The send record of issue 234 is now readable only through the controller's
verbs (issue 506), and only plan said it. status says per machine when it was
last sent a declaration, by whom, from which generation and what it answered;
node show says it in full with the refusal's words. A machine's answer is read
from its report only when that report is about the send and came after it.

cmd/mesh-controller/status.go

@@ -341,6 +341,10 @@ func printStatus(asked answers) error {
 			"lists them, and each is in its condition's tried\n\n", asked.heals.Acts, asked.heals.Escalated)
 	}
 
+	// What each machine was last sent and by whom, one line each (novox/hq issue 485). Not a fault, so it does not
+	// break "all well"; a record that could not be read does.
+	printLastSends(nodes, asked.lastSent, asked.lastSentUnread)
+
 	if adopted := adoptedNodes(nodes); len(adopted) > 0 {
 		// Said, because nothing forces the flip: a node left adopted is visible here rather than
 		// read as converged (novox/hq ADR 0100). Not a fault, so it does not break "all well".
@@ -485,6 +489,12 @@ func theThreeQuestions(ctx context.Context, open *stores) (answers, error) {
 		out.pendingUnread = err.Error()
 		err = nil
 	}
+	// And what each machine was last sent, by whom (novox/hq issue 485): the record of sends is read through
+	// the controller's verbs alone, the store's reader being shut out of its tables. Unreadable is said.
+	if out.lastSent, err = inv.LastSends(ctx); err != nil {
+		out.lastSentUnread = err.Error()
+		err = nil
+	}
 	out.plans, err = inv.RecentPlans(ctx, 5)
 	if err != nil {
 		return answers{}, err
@@ -617,7 +627,8 @@ func (a answers) well() bool {
 	return len(a.wrong) == 0 && len(a.quiet) == 0 && len(a.behind) == 0 &&
 		len(a.waiting) == 0 && len(a.refused) == 0 && a.network == "" && len(a.untaken) == 0 && len(a.leftOut) == 0 &&
 		len(a.filtered) == 0 && len(a.unheld) == 0 && len(a.overflowing) == 0 &&
-		len(a.conditions) == 0 && a.conditionsUnread == "" && a.pendingUnread == "" && !pendingOpen(a.pending)
+		len(a.conditions) == 0 && a.conditionsUnread == "" && a.pendingUnread == "" && !pendingOpen(a.pending) &&
+		a.lastSentUnread == ""
 }
 
 // pendingOpen is whether any pending assignment is still to be made. One that ended without being made is