Bound a consumer's identity by the provision it requires (hq issue 263)

The one global 20-character bound made every consumer pay an object
store's key length, even for provisions that keep no name, and a single
overflow refused the provider's whole declaration. An offer now states
its own bound (identity: {max, in} or false); unsaid, a provider told its
consumers keeps 20 and one told nothing keeps none. module check judges
every identity on the longest machine name before merge, and a provider
leaves an overflowing consumer out of its grants and composes, with the
consumer named by push, plan and status (ADR 0225).

cmd/mesh-controller/readable.go

@@ -83,6 +83,9 @@ type meshStatus struct {
 	// document without this called the mesh well while the identity provider refused every consumer
 	// for a day (04-ISSUES/179).
 	Failing []inventory.ProviderStanding `json:"failing,omitempty"`
+	// Overflowing is every module whose identity overflows the bound of a provision it requires, and
+	// so is left out of its provider's grants (novox/hq ADR 0225). Absent when every identity fits.
+	Overflowing []catalogue.Overflow `json:"overflowing,omitempty"`
 }
 
 // machineFiltered is one rule set on a converged machine that the mesh did not write and that
@@ -216,6 +219,7 @@ func statusAsJSON(asked answers) ([]byte, error) {
 	}
 	out.Unheld = asked.unheld
 	out.Failing = asked.failing
+	out.Overflowing = asked.overflowing
 	for name := range asked.refused {
 		out.Unresolved = append(out.Unresolved, machineUnresolved{
 			Node: name, Problem: asked.refused[name]})