A routed name resolves to the node whose proxy serves it, never to a provider merely told it (hq 178)

The names region attributed a composed name to whichever labelled contribution a map yielded last.
A dashboard contributes its label to its route and to the identity provider, which must know the
public name for a redirect; so on one plan grafana.<domain> pointed at the proxy's machine and on
the next at the identity provider's, and the whole region flipped with it (forge issue 227). And a
module routed several times contributed no name at all, because the single-value reading of its
contributions is empty for the many shape.

Now every node's resolution is read first and the names are attributed across them at once: the
terminus serves the name — the provider that is not itself published under a labelled name through
another — walked in order, so one mesh yields one region. Name-agnostic, structural, deterministic.

internal/catalogue/names_served.go

@@ -0,0 +1,124 @@
+package catalogue
+
+import (
+	"sort"
+	"strings"
+)
+
+// Which machine serves each routed name (novox/hq ADR 0066, issue 178).
+//
+// A routed name is a label the mesh composed for a consumer's endpoint, and it is *served* by the
+// provider that answers requests for it — the proxy the consumer's route reaches. The same name is
+// composed into every labelled contribution the consumer makes, because a provider that must know
+// the consumer's public name (an identity provider composing a redirect) is told it the same way
+// (04-ISSUES/122). Attributing the name to whichever of those providers a map happened to yield
+// last sent a public name to the identity provider's machine on one plan and to the proxy's on the
+// next (forge issue 227), and the whole names region flipped with it.
+//
+// **The terminus serves the name.** Among the providers a name reaches, the one that serves it is
+// the one that is not itself routed: a provider that contributes a labelled name of its own to some
+// requirement is published through another provider, and is a consumer of names, not their end.
+// Name-agnostic — nothing here knows what "route" means — and structural: it reads the graph the
+// modules declared. Deterministic: names, requirements and nodes are walked in order, so two
+// plans of one mesh yield one region.
+
+// NamesServed is every routed name across the mesh and the node that serves it, from every node's
+// resolution and settings. A name several termini claim goes to the first node in name order, so
+// the answer is stable; a name nothing terminal claims is left out.
+func NamesServed(plans map[string]Resolution, settings map[string]SettingsBy) (map[string]string, error) {
+	nodes := make([]string, 0, len(plans))
+	for n := range plans {
+		nodes = append(nodes, n)
+	}
+	sort.Strings(nodes)
+
+	out := map[string]string{}
+	for _, node := range nodes {
+		plan := plans[node]
+		all, err := plan.contributions(settings[node], nil, nil)
+		if err != nil {
+			return nil, err
+		}
+		requirements := make([]string, 0, len(all))
+		for to := range all {
+			requirements = append(requirements, to)
+		}
+		sort.Strings(requirements)
+		for _, to := range requirements {
+			for _, given := range all[to] {
+				if given.Node != "" {
+					// Said from another machine; that machine's own resolution carries it.
+					continue
+				}
+				// A routed name, and only that: a contribution the mesh composed a name for from a
+				// label it was given. A grant that happens to carry a `name` of its own — a database
+				// name — carries no label and is left alone.
+				if _, labelled := given.Values["label"]; !labelled {
+					continue
+				}
+				name, _ := given.Values["name"].(string)
+				if name == "" {
+					continue
+				}
+				serving := servingNodeOf(plan, to, given.From, node)
+				if !servesNames(plans[serving], to) {
+					continue
+				}
+				name = strings.ToLower(name)
+				if held, taken := out[name]; !taken || serving < held {
+					out[name] = serving
+				}
+			}
+		}
+	}
+	return out, nil
+}
+
+// servingNodeOf is the node answering one consumer's requirement: whoever the plan needs it from,
+// or this same node when the provider is beside the consumer.
+func servingNodeOf(plan Resolution, requirement, consumer, self string) string {
+	for _, need := range plan.Needs {
+		if need.Name == requirement && need.For == consumer && need.From != "" {
+			return need.From
+		}
+	}
+	return self
+}
+
+// servesNames says whether the module providing a requirement on a node is a terminus: it is not
+// itself published under a labelled name through some other provider. A node whose plan is not
+// known (it did not resolve) serves nothing.
+func servesNames(plan Resolution, requirement string) bool {
+	for _, m := range plan.Modules {
+		if !offers(m, requirement) {
+			continue
+		}
+		return !contributesALabel(m)
+	}
+	return false
+}
+
+func offers(m Manifest, requirement string) bool {
+	for _, o := range m.Offers() {
+		if o == requirement {
+			return true
+		}
+	}
+	return false
+}
+
+func contributesALabel(m Manifest) bool {
+	for _, values := range m.Contributes {
+		if _, labelled := values["label"]; labelled {
+			return true
+		}
+	}
+	for _, locals := range m.ContributesMany {
+		for _, values := range locals {
+			if _, labelled := values["label"]; labelled {
+				return true
+			}
+		}
+	}
+	return false
+}