Share resolved companion contexts by tier

docs/roadmap/remediation.md

@@ -218,6 +218,8 @@ declarations, and existing diagnostic sites.
 
 ## Finding 7 — Each derived companion keeps a copy of the same tier context
 
+**Status** — Complete. Each tier creates at most one shared derived context and has no per-input context table. The development check and full race suite passed.
+
 **Priority P3.** `acquireUnderlayGroupScopes` allocates a context pointer
 slot for every input, even in tiers with no bindings. Each derived input
 then gets an addressable copy of the same main context with the same

internal/engine/import_acquisition.go

@@ -38,31 +38,30 @@ func acquireImportedInput(request importAcquisitionRequest, policy *acquisitionP
 	source := request.input.input.source
 	context := request.input.input.filesystem
 	main := request.main
-	resolved, diagnostic := resolvedFilesystemContext{}, (*Diagnostic)(nil)
-	if request.input.resolved != nil {
-		resolved = *request.input.resolved
-	} else {
-		resolved, diagnostic = resolveFilesystemContext(source, context, main, tier.hostToken)
-	}
-	if diagnostic != nil {
-		return nil, sourceInfos(main.source), nil, []Diagnostic{*diagnostic}
+	resolved := request.input.resolved
+	if resolved == nil {
+		value, diagnostic := resolveFilesystemContext(source, context, main, tier.hostToken)
+		if diagnostic != nil {
+			return nil, sourceInfos(main.source), nil, []Diagnostic{*diagnostic}
+		}
+		resolved = &value
 	}
 	if resolved.native == nil {
-		if diagnostic := validateResolvedFilesystemDirectories(resolved); diagnostic != nil {
+		if diagnostic := validateResolvedFilesystemDirectories(*resolved); diagnostic != nil {
 			return nil, sourceInfos(main.source), nil, []Diagnostic{*diagnostic}
 		}
 	}
-	access, err := openResolvedFilesystemAccess(resolved)
+	access, err := openResolvedFilesystemAccess(*resolved)
 	if err != nil {
 		diagnostic := globFilesystemDiagnostic(err, "configuration root could not be opened", Location{})
 		diagnostic.Primary = nil
 		return nil, sourceInfos(main.source), nil, []Diagnostic{diagnostic}
 	}
-	composition, sources, diagnostics := acquireImportedWithAccess(request, policy, state, tier, access, resolved)
+	composition, sources, diagnostics := acquireImportedWithAccess(request, policy, state, tier, access, *resolved)
 	if len(diagnostics) != 0 {
 		return composition, sources, nil, diagnostics
 	}
-	return composition, sources, &resolved, nil
+	return composition, sources, resolved, nil
 }
 
 func acquireImportedWithAccess(request importAcquisitionRequest, policy *acquisitionPolicy, loadState *acquisitionState, tier *tierAcquisitionState, access *filesystemAccess, resolved resolvedFilesystemContext) (*composedDocument, []SourceInfo, []Diagnostic) {

internal/engine/load_request.go

@@ -276,23 +276,27 @@ func applyCompletedTier(
 func acquireUnderlayGroupScopes(group loadGroup, index int, rule *VersionRule, state *acquisitionState, policy acquisitionPolicy, mainContext *resolvedFilesystemContext) (*acquiredUnderlayGroup, []Diagnostic) {
 	initialBytes, initialNodes := state.accounting.bytes, state.accounting.nodes
 	tier := &tierAcquisitionState{visited: make(map[resourceIdentity]importRoute), hostToken: &namespaceToken{}}
-	selected := make([]*resolvedFilesystemContext, len(group.inputs))
-	for i, contribution := range group.inputs {
-		if contribution.filesystem == nil && contribution.mainRelative != nil && mainContext != nil {
-			derived := *mainContext
-			derived.mainPath = ""
-			derived.hostToken = tier.hostToken
-			selected[i] = &derived
-		} else if contribution.filesystem == nil && contribution.mainRelative != nil {
-			group.inputs[i].filesystem = contribution.mainRelative.Fallback
+	var derived *resolvedFilesystemContext
+	bind := func(input loadInput) (loadInput, *resolvedFilesystemContext) {
+		if input.filesystem != nil || input.mainRelative == nil {
+			return input, nil
 		}
+		if mainContext == nil {
+			input.filesystem = input.mainRelative.Fallback
+			return input, nil
+		}
+		if derived == nil {
+			context := *mainContext
+			context.mainPath = ""
+			context.hostToken = tier.hostToken
+			derived = &context
+		}
+		return input, derived
 	}
 	nativeAnchors := make(map[*namespaceToken]string)
 	for inputIndex, contribution := range group.inputs {
-		token := nativeTokenForLoadInput(contribution)
-		if selected[inputIndex] != nil && selected[inputIndex].native != nil {
-			token = selected[inputIndex].native.token
-		}
+		contribution, resolved := bind(contribution)
+		token := nativeTokenForLoadInput(contribution, resolved)
 		if token != nil {
 			if _, exists := nativeAnchors[token]; !exists {
 				nativeAnchors[token] = explicitNamespaceAnchor(index, inputIndex+1)
@@ -302,10 +306,11 @@ func acquireUnderlayGroupScopes(group loadGroup, index int, rule *VersionRule, s
 	acquiredGroup := &acquiredUnderlayGroup{index: index}
 	inclusionGraph := newImportInclusionGraph()
 	for inputIndex, contribution := range group.inputs {
+		contribution, resolved := bind(contribution)
 		acquired, diagnostics := acquireInput(inputAcquisitionRequest{
 			input: contribution, role: sourceVersionContribution,
-			resolved:         selected[inputIndex],
-			withoutBase:      contribution.mainRelative != nil && contribution.filesystem == nil && selected[inputIndex] == nil,
+			resolved:         resolved,
+			withoutBase:      contribution.mainRelative != nil && contribution.filesystem == nil && resolved == nil,
 			directiveContext: rootDirectiveContextLayered, protectionRule: rule,
 		}, policy, state, tier)
 		for _, source := range acquired.sources {
@@ -324,10 +329,7 @@ func acquireUnderlayGroupScopes(group loadGroup, index int, rule *VersionRule, s
 			kind: "host", host: explicitNamespaceAnchor(index, 0),
 			input: explicitNamespaceAnchor(index, inputIndex+1),
 		}
-		token := nativeTokenForLoadInput(contribution)
-		if selected[inputIndex] != nil && selected[inputIndex].native != nil {
-			token = selected[inputIndex].native.token
-		}
+		token := nativeTokenForLoadInput(contribution, resolved)
 		if token != nil {
 			anchors.kind = "native"
 			anchors.native = nativeAnchors[token]
@@ -411,7 +413,10 @@ func composeUnderlayGroup(acquired *acquiredUnderlayGroup, rule *VersionRule, po
 	return composition, nil
 }
 
-func nativeTokenForLoadInput(input loadInput) *namespaceToken {
+func nativeTokenForLoadInput(input loadInput, resolved *resolvedFilesystemContext) *namespaceToken {
+	if resolved != nil && resolved.native != nil {
+		return resolved.native.token
+	}
 	if input.source.kind == sourceFilesystem && input.source.namespace != nil {
 		return input.source.namespace.token
 	}