The board says what is waiting too, or it disagrees with the command

Adding "not running what the mesh would send it" to `status` and not to the
board would have left two answers to one question with a person in front of
each — which is the single thing this page's design forbids, introduced by the
change that was supposed to make the question answerable.

The published JSON carries it as well, so the page, the command and anything
built against either say the same thing from the same read. Additive, because
that shape is hard to change once anything is built against it.

Never told stays separate from out of date on the page as it is everywhere
else: same remedy, and nobody has ever asked that machine to be anything.

cmd/mesh-control/readable.go

@@ -31,6 +31,10 @@ type meshStatus struct {
 	Quiet []machineQuiet `json:"quiet"`
 	// Behind is every module built from something older than its source has.
 	Behind []moduleBehind `json:"behind"`
+	// Waiting is every machine not running what the mesh would send it. The same question as
+	// Behind one level down: that says the catalogue is old, this says a machine is — and only
+	// this one has somebody's change waiting inside it.
+	Waiting []machineWaiting `json:"waiting"`
 	// Machines is how many the mesh knows about, so a reader can tell "none wrong" from
 	// "none at all".
 	Machines int `json:"machines"`
@@ -50,6 +54,14 @@ type machineDoing struct {
 	At      time.Time `json:"at"`
 }
 
+type machineWaiting struct {
+	Node string `json:"node"`
+	// Never is true when nothing has ever been sent to it. Not out of date: nobody has ever asked
+	// this machine to be anything, and the two read differently to whoever is looking.
+	Never bool       `json:"never"`
+	Sent  *time.Time `json:"sent,omitempty"`
+}
+
 type machineQuiet struct {
 	Node string `json:"node"`
 	// LastSeen is absent when the machine has never spoken, which is a different thing from
@@ -66,10 +78,16 @@ type moduleBehind struct {
 
 // statusAsJSON answers the same three questions as the text form, from the same calls.
 func statusAsJSON(wrong []inventory.Doing, nodes []inventory.Node, quiet []inventory.Node,
-	behind map[string][]string, sources map[string]inventory.Source) ([]byte, error) {
+	behind map[string][]string, sources map[string]inventory.Source,
+	waiting []inventory.Machine) ([]byte, error) {
 
 	out := meshStatus{Machines: len(nodes), Wrong: []machineDoing{},
-		Quiet: []machineQuiet{}, Behind: []moduleBehind{}}
+		Quiet: []machineQuiet{}, Behind: []moduleBehind{}, Waiting: []machineWaiting{}}
+
+	for _, m := range waiting {
+		out.Waiting = append(out.Waiting, machineWaiting{
+			Node: m.Node, Never: m.Never, Sent: m.SentAt})
+	}
 
 	for _, d := range wrong {
 		row := machineDoing{