A command opens each store once, not once per machine

Working out what a machine should be reaches the identity context for its
certificate and the licence context for its model access. Both were opened —
and waited on — inside functions called for every node in a push. Two machines
hid it. Fifty would be fifty connect-and-wait cycles for data that does not
change while the push runs.

So a command holds what it has open, and passes it. Each context is opened on
first use rather than up front, because most commands need one and paying to
reach three would be the same waste from the other side.

The contexts stay separate, which is the point: this is one struct holding
three connections to three databases, not one connection to a shared one. No
context reaches another's store, and each still holds only its own credential
(novox/hq ADR 0008).

A pure move again — the gate is green before and after, and no test changed.

cmd/mesh-control/status.go

@@ -40,13 +40,13 @@ func statusCommand(ctx context.Context, args []string) error {
 		return err
 	}
 
-	inv, err := openInventory(ctx)
+	open, err := openStores(ctx)
 	if err != nil {
 		return err
 	}
-	defer inv.Close()
+	defer open.Close()
 
-	asked, err := theThreeQuestions(ctx, inv)
+	asked, err := theThreeQuestions(ctx, open)
 	if err != nil {
 		return err
 	}
@@ -171,7 +171,8 @@ type builds struct{ inv *inventory.Inventory }
 // The order is the design and not a convenience: is anything broken, is anything not answering, is
 // anything out of date. The first has consequences now, the second may, the third is a plan for
 // later — and anything that led with the third would bury the first.
-func theThreeQuestions(ctx context.Context, inv *inventory.Inventory) (answers, error) {
+func theThreeQuestions(ctx context.Context, open *stores) (answers, error) {
+	inv := open.inventory
 	var out answers
 	var err error
 
@@ -198,7 +199,7 @@ func theThreeQuestions(ctx context.Context, inv *inventory.Inventory) (answers,
 	// And which machines are not running what the mesh would send them. The same question as a
 	// module being behind its source, one level down: that one says the catalogue is out of date,
 	// this one says a machine is — and only the second has anybody's change waiting in it.
-	would, err := wouldSend(ctx, inv, out.nodes)
+	would, err := wouldSend(ctx, open, out.nodes)
 	if err != nil {
 		return answers{}, err
 	}