Clarify load context and inheritance handoffs

internal/engine/load_input.go

@@ -129,6 +129,55 @@ func applyInputLayers(source Source, filesystem *FilesystemContext, overlay stri
 	return input, nil
 }
 
+func completeOrdinaryResourceContexts(input assembledInput, main loadInput) (assembledInput, []Diagnostic) {
+	baseSources := make([]SourceInfo, 0, len(input.sources))
+	for _, source := range input.sources {
+		if source.Layer == LayerBase {
+			baseSources = append(baseSources, source)
+		}
+	}
+	if len(baseSources) == 0 || input.contexts[baseSources[0].ID].FS != nil {
+		return input, nil
+	}
+	if input.resolvedFilesystem == nil && (main.source.kind == sourceFile || main.filesystem != nil || nativeContext(main.source, main.filesystem)) {
+		resolved, diagnostic := resolveFilesystemContext(main.source, main.filesystem, input.parsed, nil)
+		if diagnostic != nil {
+			return input, []Diagnostic{*diagnostic}
+		}
+		input.resolvedFilesystem = &resolved
+	}
+	contexts, diagnostic := contextsForResolvedSources(input.resolvedFilesystem, baseSources)
+	if diagnostic != nil {
+		return input, []Diagnostic{*diagnostic}
+	}
+	mergeResourceContexts(&input.contexts, contexts)
+	return input, nil
+}
+
+func expandStructuralInheritance(input assembledInput, protectionRule *VersionRule, policy sequencePolicy) (assembledInput, *VersionRule, bool, []Diagnostic) {
+	if input.document == nil || !containsInheritanceDirective(input.document) {
+		return input, nil, false, nil
+	}
+	composition, diagnostics := compositionForInput(input)
+	if len(diagnostics) != 0 {
+		return input, nil, false, diagnostics
+	}
+	expanded, diagnostics := expandInheritanceWithCollectionRules(
+		composition.root, composition.origins, composition.collectionPolicies, policy, defaultProjectionLimits(),
+	)
+	if len(diagnostics) != 0 {
+		return input, nil, false, diagnostics
+	}
+	effectiveVersion, diagnostic := projectInheritanceVersion(protectionRule, expanded)
+	if diagnostic != nil {
+		return input, nil, false, []Diagnostic{*diagnostic}
+	}
+	input.composition = composition
+	input.inheritance = expanded
+	input.document = expanded.root
+	return input, effectiveVersion, true, nil
+}
+
 // compositionForInput initializes the structural handoff used by inheritance
 // expansion. Raw source bytes and mapping keys retain their budgets.
 func compositionForInput(input assembledInput) (*composedDocument, []Diagnostic) {