Say a module assigned and left out of its machine's composition as a condition (issue 380)

A push leaves out a module whose settings do not compose and sends the rest,
which is right, but only plan said so: nfs-server ran nowhere for days while
the operator believed it ran. The self-check now raises needs-operator for a
setting nobody gave, naming the setting and the command, and left-out for any
other cause; both warnings, cleared once the module composes or is unassigned.
status and node show list the same modules as assigned, not applied.

internal/catalogue/declaration.go

@@ -342,18 +342,38 @@ func (e *NotMadeError) Error() string {
 // compose. Empty when every module composes. The same judgement SetSettings makes before storing.
 func (r Resolution) LeftOut(settings SettingsBy, adopted bool) map[string]string {
 	out := map[string]string{}
+	for module, why := range r.LeftOutBecause(settings, adopted) {
+		out[module] = why.Error()
+	}
+	return out
+}
+
+// LeftOutBecause is LeftOut with each reason as the error it was, so a reader can tell a setting nobody
+// gave (an *UnsetSettingError) from any other cause and say it as the operator's to give (novox/hq issue
+// 380). An UnreadManifestError for a stored manifest this controller cannot read whole.
+func (r Resolution) LeftOutBecause(settings SettingsBy, adopted bool) map[string]error {
+	out := map[string]error{}
 	for _, m := range r.Modules {
 		if why := UnknownFieldReason(m); why != "" {
-			out[m.Module] = why
+			out[m.Module] = &UnreadManifestError{Module: m.Module, said: why}
 			continue
 		}
 		if err := JudgeSettings(m, settings[m.Module], adopted); err != nil {
-			out[m.Module] = err.Error()
+			out[m.Module] = err
 		}
 	}
 	return out
 }
 
+// UnreadManifestError is a module left out because its stored manifest has a key this controller does not know
+// (novox/hq ADR 0262): said once for the whole mesh, by the catalogue's own condition, not per machine.
+type UnreadManifestError struct {
+	Module string
+	said   string
+}
+
+func (e *UnreadManifestError) Error() string { return e.said }
+
 // Compose is Declaration with the owner of every resource said.
 func (r Resolution) Compose(with Rendering) (Composed, error) {
 	owner := map[string]string{}

internal/catalogue/setting_into.go

@@ -38,6 +38,17 @@ func settingsUsed(content string) []string {
 	return keys
 }
 
+// UnsetSettingError is a module whose definition says ${setting:<key>} where nothing sets that key: typed, so
+// that whoever reads why a module was left out of a machine can tell a setting nobody gave — the operator's
+// to give, named with the command that gives it — from any other reason (novox/hq issue 380). Its words are
+// the refusal's, unchanged.
+type UnsetSettingError struct {
+	Module, Setting string
+	said            string
+}
+
+func (e *UnsetSettingError) Error() string { return e.said }
+
 // settingInto fills a file's ${setting:…} placeholders from the layers over a module.
 //
 // The last layer setting a key wins, which is the node's over the mesh's over the module's own
@@ -58,12 +69,12 @@ func settingInto(resource map[string]any, layers []Layer, module string) error {
 	for _, key := range settingsUsed(content) {
 		value, set := settingValue(layers, key)
 		if !set {
-			return fmt.Errorf(
+			return &UnsetSettingError{Module: module, Setting: key, said: fmt.Sprintf(
 				"%s has a file that says ${setting:%s}, and nothing sets %q for it — an operator's "+
 					"value is the assignment's, never the definition's (novox/hq ADR 0112), and only a "+
 					"preference has a default in the definition (ADR 0262): "+
 					"`settings set %s <file>` with {%q: …}%s",
-				module, key, key, module, key, orNoSettings(layers))
+				module, key, key, module, key, orNoSettings(layers))}
 		}
 		content = strings.ReplaceAll(content, "${setting:"+key+"}", plainly(value))
 	}
@@ -114,11 +125,11 @@ func settingIntoUnit(resource map[string]any, layers []Layer, module string) err
 	for _, key := range settingsUsed(unit) {
 		value, set := settingValue(layers, key)
 		if !set {
-			return fmt.Errorf(
+			return &UnsetSettingError{Module: module, Setting: key, said: fmt.Sprintf(
 				"%s has a service whose unit says ${setting:%s}, and nothing sets %q for it — an operator's "+
 					"value is the assignment's, never the definition's (novox/hq ADR 0112): "+
 					"`settings set %s <file>` with {%q: …}%s",
-				module, key, key, module, key, orNoSettings(layers))
+				module, key, key, module, key, orNoSettings(layers))}
 		}
 		v := plainly(value)
 		if !unitPart.MatchString(v) {