Compose a node's own modules from their builds and read what providers elsewhere serve, so a self-composing node hands moved modules and settles served settings as the controller does (issue 1126)

frombus composed every module from the indexer's raw manifest: no moved module
was handed, so the node stood in for own secrets the vault leaves to the
provisioner (the seed's refusals on all four nodes), and a provider elsewhere
had no config values, so mailu's served domain refused shanks.

- takein: the controller's take-in of a done key (artifacts, launchers, the
  templates archive's texts, Resolve) as one SDK rule; catalogue.Launchers holds
  the launcher rule buildstep now delegates to.
- frombus: each module placed on the composing node, and each kept at another
  build (Scope.KeptAt, a fingerprint), composes from its built manifest; another
  node's modules give the keys their served values fill (Reader.Served).
- buscompose: Declared.Served and Principal.ServedReads grant every node the read
  of exactly those keys of mesh-config_resolved.
- compose.ArtifactStoreAddress: the store as the node's composition routes to it.

go/compose/rendering.go

@@ -325,6 +325,13 @@ func (c *composer) artifactStoreOnNetwork(on map[string]bool) (node, port string
 	return "", "", false, nil
 }
 
+// ArtifactStoreAddress is the artifact store as node reaches it, by the rule its composition routes every kept reference
+// with (artifactStoreAddress): empty when node reaches none. A node composing its own modules reads a templates archive
+// there (issue 1126).
+func ArtifactStoreAddress(in Input, node string) (string, error) {
+	return newComposer(in).artifactStoreAddress(node)
+}
+
 // artifactStoreAddress is the artifact store as `forNode` reaches it: `<node>.internal:<port>` over the private network, or
 // `127.0.0.1:<port>` for the node that holds the store itself when nothing is on the network yet, and empty for any other
 // (novox/hq 04-ISSUES/102).