A setting reaches only what declares it, the mesh places its own files, registration refuses a name

Three of novox/hq's group-4 leftovers, one branch.

Issue 173: a module's settings reached every route it contributed, every database it asked for and
every served fact its consumers read — a mail server's site name arrived at the proxy as a route
fact. A setting now overrides a key a contribution or served fact declares and adds none; a file
still merges any key, and a key nothing takes is named as stray instead of dropped silently.

Issue 174: the mesh's own files for a module — its bus credential, its merged config, its bindings —
were placed by the definition under /var/lib/mesh/<module>, 232 host paths in 50 definitions. A
directory may now say `place: "mesh"` and resolves to <root>/mesh/<module>; a directory beneath a
placed one may state its path as `${dir:<id>}/<rest>` and moves with it. The proof test resolves
both catalogues and compares: 48 definitions, no path moved. The controller's own manifest is
converted here; the catalogue in mesh-catalog.

ADR 0155: the installation check moves to registration. `module add` and a build's result both
refuse a definition that names an installation, in the check's words, with the way out; the build
stays recorded.

internal/catalogue/settings_test.go

@@ -167,11 +167,45 @@ func TestSettingsThatReachNothingAreNamed(t *testing.T) {
 		{"id": "conf", "type": "file", "path": "/etc/thing", "content": "plain"},
 	}}
 	unused := UnusedSettings(m, []Layer{{From: "node", Values: map[string]any{"port": 1}}})
-	if len(unused) != 1 || !strings.Contains(unused[0], "no file or contribution to merge it into") {
+	if len(unused) != 1 || !strings.Contains(unused[0], "no file that merges it") {
 		t.Errorf("settings that reached nothing were not named: %v", unused)
 	}
 }
 
+func TestASettingLandsOnlyWhereSomethingDeclaresIt(t *testing.T) {
+	// novox/hq 04-ISSUES/173. A module that contributes a route and serves a provision takes a
+	// setting for a key either declares, and a setting for a key neither declares is stray — it
+	// would not reach the route or the served fact, so it must be said rather than dropped.
+	m := Manifest{Module: "mail",
+		Contributes: map[string]map[string]any{"reverse-proxy": {"host": "mail", "port": 8080}},
+		Serves:      map[string]map[string]any{"smtp": {"host": "mail", "port": 25}},
+		Resources: []map[string]any{
+			{"id": "env", "type": "file", "path": "/etc/mail.env", "content": "SITE=${setting:sitename}\n"},
+		}}
+	layers := []Layer{{From: "the mesh", Values: map[string]any{
+		"host": "post", "sitename": "Mail", "website": "https://www.example.tld"}}}
+	unused := UnusedSettings(m, layers)
+	if len(unused) != 1 || !strings.Contains(unused[0], `"website"`) {
+		t.Errorf("only website reaches nothing; named: %v", unused)
+	}
+}
+
+func TestASettingOverridesAServedKeyAndAddsNone(t *testing.T) {
+	// What a consumer is told is the provider's contract. A setting made for one of the
+	// provider's files — its site name, its public address — is not part of it.
+	served, err := Settle(map[string]any{"host": "mail", "port": 25},
+		[]Layer{{From: "the mesh", Values: map[string]any{"host": "post", "sitename": "Mail"}}})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if served["host"] != "post" {
+		t.Errorf("the setting did not override the served host: %v", served)
+	}
+	if _, leaked := served["sitename"]; leaked {
+		t.Errorf("a setting for a file reached the consumers: %v", served)
+	}
+}
+
 func TestContentThatIsNotJSONIsRefusedWhereSomebodyIsLooking(t *testing.T) {
 	// Rather than on the machine, at apply time, as a file the program cannot read.
 	_, err := ApplySettings(file(`this is not json`), nil)