diff --git a/docs/roadmap/implementation.md b/docs/roadmap/implementation.md
index 902e25f..54a05ed 100644
--- a/docs/roadmap/implementation.md
+++ b/docs/roadmap/implementation.md
@@ -129,6 +129,8 @@ selection, and diagnostic tests for verification.
 
 ## Stage 4 — Finish companion handling when no base exists
 
+**Status:** Complete. Focused no-base, import, placement, and grouped-load checks passed.
+
 Handle the no-base outcome only for an active underlay binding with no
 override, usable main context, or fallback. `RequireBase` fails with
 `CodeOptionsInvalid` regardless of import enablement or declaration count.
diff --git a/facade_main_relative_test.go b/facade_main_relative_test.go
index 3d92f9b..4ee823a 100644
--- a/facade_main_relative_test.go
+++ b/facade_main_relative_test.go
@@ -68,3 +68,91 @@ func TestMainRelativeContextSelection(t *testing.T) {
 		t.Fatalf("fallback value = %q", got)
 	}
 }
+
+func TestMainRelativeWithoutBase(t *testing.T) {
+	tests := []struct {
+		name, source string
+		requireBase  bool
+		wantCode     configkit.Code
+	}{
+		{"optional", "config: {imports: [{path: missing.yml}]}\ncount: 7\n", false, ""},
+		{"required", "config: {imports: [{path: missing.yml, required: true}]}\n", false, configkit.CodeImportMissing},
+		{"required directory", "config: {imports: [{dir: missing, required: true}]}\n", false, configkit.CodeImportMissing},
+		{"required glob", "config: {imports: [{glob: '*.yml', required: true}]}\n", false, configkit.CodeImportMissing},
+		{"empty required", "config: {imports: [{path: [], required: true}]}\ncount: 7\n", false, ""},
+		{"base required", "count: 7\n", true, configkit.CodeOptionsInvalid},
+	}
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			input := configkit.Input{Source: configkit.Bytes("companion", []byte(test.source)), Imports: true, MainRelative: &configkit.MainRelativeContext{RequireBase: test.requireBase}}
+			result, err := configkit.LoadLayered(configkit.Input{Source: configkit.NoSource()}, configkit.LayeredOptions[layeredFacadeConfig]{Underlays: []configkit.Underlay{{Inputs: []configkit.Input{input}}}})
+			if test.wantCode != "" {
+				if err == nil {
+					t.Fatal("expected failure")
+				}
+				for _, d := range err.(*configkit.LoadError).Diagnostics() {
+					if d.Code == test.wantCode {
+						return
+					}
+				}
+				t.Fatalf("diagnostics: %#v", err.(*configkit.LoadError).Diagnostics())
+			}
+			if err != nil {
+				t.Fatalf("%v: %#v", err, err.(*configkit.LoadError).Diagnostics())
+			}
+			if result.Config.Count != 7 {
+				t.Fatalf("config = %#v", result.Config)
+			}
+			if sources := result.Sources(); len(sources) != 1 || len(sources[0].EmptyImportSelections) != 0 {
+				t.Fatalf("sources = %#v", sources)
+			}
+		})
+	}
+}
+
+func TestMainRelativeWithoutBaseSequenceItem(t *testing.T) {
+	type item struct {
+		Name string `yaml:"name"`
+	}
+	type config struct {
+		Items []item `yaml:"items"`
+	}
+	input := configkit.Input{Source: configkit.Bytes("item", []byte("config: {imports: [{path: missing.yml}]}\nname: example\n")), Imports: true, MainRelative: configkit.MainRelative(), Destination: configkit.Keys("items"), PlacementMode: configkit.PlacementModeSequenceItem}
+	result, err := configkit.LoadLayered(configkit.Input{Source: configkit.NoSource()}, configkit.LayeredOptions[config]{Underlays: []configkit.Underlay{{Inputs: []configkit.Input{input}}}})
+	if err != nil {
+		t.Fatalf("%v: %#v", err, err.(*configkit.LoadError).Diagnostics())
+	}
+	if len(result.Config.Items) != 1 || result.Config.Items[0].Name != "example" {
+		t.Fatalf("config = %#v", result.Config)
+	}
+}
+
+func TestMainRelativeWithoutBaseImportDefaults(t *testing.T) {
+	required := true
+	tests := []struct {
+		name, source string
+		imports      bool
+		requireBase  bool
+		code         configkit.Code
+	}{
+		{"default required", "config: {imports: [{path: missing.yml}]}\n", true, false, configkit.CodeImportMissing},
+		{"malformed", "config: {imports: [{path: 42}]}\n", true, false, configkit.CodeImportInvalid},
+		{"imports disabled", "config: {imports: [{path: missing.yml}]}\n", false, false, configkit.CodeImportDisabled},
+		{"base required without imports", "count: 1\n", false, true, configkit.CodeOptionsInvalid},
+	}
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			input := configkit.Input{Source: configkit.Bytes("companion", []byte(test.source)), Imports: test.imports, MainRelative: &configkit.MainRelativeContext{RequireBase: test.requireBase}}
+			_, err := configkit.LoadLayered(configkit.Input{Source: configkit.NoSource()}, configkit.LayeredOptions[layeredFacadeConfig]{ImportDefaults: configkit.ImportDefaults{Required: &required}, Underlays: []configkit.Underlay{{Inputs: []configkit.Input{input}}}})
+			if err == nil {
+				t.Fatal("expected failure")
+			}
+			for _, diagnostic := range err.(*configkit.LoadError).Diagnostics() {
+				if diagnostic.Code == test.code {
+					return
+				}
+			}
+			t.Fatalf("diagnostics = %#v", err.(*configkit.LoadError).Diagnostics())
+		})
+	}
+}
diff --git a/internal/engine/acquisition.go b/internal/engine/acquisition.go
index 811d855..f99f8c0 100644
--- a/internal/engine/acquisition.go
+++ b/internal/engine/acquisition.go
@@ -21,6 +21,7 @@ type tierAcquisitionState struct {
 type inputAcquisitionRequest struct {
 	input            loadInput
 	resolved         *resolvedFilesystemContext
+	withoutBase      bool
 	role             sourceVersionRole
 	directiveContext rootDirectiveContext
 	protectionRule   *VersionRule
@@ -34,6 +35,9 @@ type importAcquisitionRequest struct {
 }
 
 func acquireInput(request inputAcquisitionRequest, policy acquisitionPolicy, state *acquisitionState, tier *tierAcquisitionState) (assembledInput, []Diagnostic) {
+	if request.withoutBase && request.input.mainRelative.RequireBase {
+		return assembledInput{}, []Diagnostic{optionDiagnostic(CodeOptionsInvalid, "main-relative input requires a filesystem base")}
+	}
 	source := request.input.source
 	destination := request.input.destination
 	accounting := state.accounting
@@ -102,7 +106,12 @@ func acquireInput(request inputAcquisitionRequest, policy acquisitionPolicy, sta
 		return input, diagnostics
 	}
 	request.input.source = selectedSource
-	if request.input.imports && selectedSource.kind != sourceNone {
+	if request.input.imports && selectedSource.kind != sourceNone && request.withoutBase {
+		input, diagnostics = acquireContextlessInput(input, request, versionProcessing, policy)
+		if len(diagnostics) != 0 {
+			return input, diagnostics
+		}
+	} else if request.input.imports && selectedSource.kind != sourceNone {
 		importRequest := importAcquisitionRequest{input: request, main: parsed, processing: versionProcessing}
 		input.composition, input.sources, input.resolvedFilesystem, diagnostics = acquireImportedInput(importRequest, &policy, state, tier)
 		if len(diagnostics) != 0 {
diff --git a/internal/engine/contextless_imports.go b/internal/engine/contextless_imports.go
new file mode 100644
index 0000000..142a516
--- /dev/null
+++ b/internal/engine/contextless_imports.go
@@ -0,0 +1,86 @@
+package engine
+
+import "go.maximumdirect.net/configkit/internal/document"
+
+func acquireContextlessInput(input assembledInput, request inputAcquisitionRequest, processing *sourceVersionProcessingResult, policy acquisitionPolicy) (assembledInput, []Diagnostic) {
+	parsed := input.parsed
+	var body *document.Node
+	var declarations []importDeclarationSpec
+	var sequences []sequenceDeclarationSpec
+	var diagnostics []Diagnostic
+	if processing != nil {
+		body, declarations = processing.payload, processing.imports
+		sequences = cloneSequenceDeclarations(processing.sequences)
+	} else {
+		body, declarations, diagnostics = splitImportDirectives(parsed.document)
+	}
+	destination := request.input.destination
+	localDestination := destination
+	if request.input.placementMode == PlacementModeSequenceItem {
+		localDestination = Path{}
+	}
+	if len(diagnostics) == 0 {
+		var policies []resolvedImportPolicy
+		policies, diagnostics = prepareImportDeclarations(declarations, policy.importDefaults, localDestination)
+		if len(diagnostics) == 0 {
+			for i, spec := range declarations {
+				if !policies[i].required || spec.selector == importSelectorPath && len(spec.paths) == 0 {
+					continue
+				}
+				site := spec.fieldSites["path"]
+				if spec.selector == importSelectorPath && len(spec.selectorSites) != 0 {
+					site = spec.selectorSites[0]
+				}
+				if spec.selector == importSelectorDirectory {
+					site = spec.fieldSites["dir"]
+				}
+				if spec.selector == importSelectorGlob {
+					site = spec.fieldSites["glob"]
+				}
+				diagnostics = []Diagnostic{{Code: CodeImportMissing, Severity: SeverityError, Path: site.path.clone(), Message: "import cannot be selected because no filesystem base is available", Primary: cloneLocation(&site.location)}}
+				break
+			}
+		}
+	}
+	if len(diagnostics) != 0 {
+		if request.input.placementMode == PlacementModeSequenceItem {
+			diagnostics = prependCompositionDiagnosticPaths(diagnostics, destination.Index(0))
+		}
+		return input, diagnostics
+	}
+	key := importKeyForMainSource(parsed.source)
+	info := cloneSourceInfo(*parsed.source)
+	accounting := input.accounting
+	accounting.sources++
+	accounting.bytes += parsed.bytes
+	accounting.nodes += countInputNodes(parsed.document)
+	limits := policy.importLimits
+	if accounting.sources > limits.sources || accounting.bytes > limits.bytes || accounting.nodes > limits.nodes {
+		return input, []Diagnostic{importDiagnostic(CodeImportLimitExceeded, "configuration exceeds the aggregate input limit", nil)}
+	}
+	contribution := acquiredContribution{source: info, payload: body, identity: key, role: importRoleMain, scopeOwner: key, processing: processing, sequenceDeclarations: sequences}
+	var scope acquisitionScope
+	if request.input.placementMode == PlacementModeSequenceItem {
+		contribution.document = body
+		local := acquisitionScope{owner: key, contributions: []acquiredContribution{contribution}}
+		scope = acquisitionScope{owner: key, destination: destination.clone(), contributions: []acquiredContribution{{source: info, payload: body, identity: key, role: importRoleMain, scopeOwner: key, destination: destination.clone(), processing: processing, sequenceDeclarations: sequences, pendingItem: &local}}}
+		if diagnostic := reservePendingItemPlacements(&scope, limits, accounting); diagnostic != nil {
+			return input, []Diagnostic{*diagnostic}
+		}
+	} else {
+		_, placed, err := placeDocument(body, destination, body.Location, maxDocumentDepth, maxDocumentNodes)
+		if err != nil {
+			return input, []Diagnostic{sourceDiagnostic(CodeSourceLimitExceeded, info.ID, "configuration exceeds the source depth or node limit after destination placement")}
+		}
+		accounting.nodes += destinationWrapperNodeCount(destination)
+		if accounting.nodes > limits.nodes {
+			return input, []Diagnostic{importDiagnostic(CodeImportLimitExceeded, "configuration exceeds the aggregate node limit", nil)}
+		}
+		contribution.document, contribution.destination = placed, destination.clone()
+		scope = acquisitionScope{owner: key, destination: destination.clone(), contributions: []acquiredContribution{contribution}}
+	}
+	input.document = body
+	input.composition = &composedDocument{acquisition: []acquisitionScope{scope}, importGraph: newImportInclusionGraph(), inputBytes: accounting.bytes, inputNodes: accounting.nodes}
+	input.acquisition = cloneAcquisitionScopes(input.composition.acquisition)
+	return input, nil
+}
diff --git a/internal/engine/load_request.go b/internal/engine/load_request.go
index ad59186..ab1681a 100644
--- a/internal/engine/load_request.go
+++ b/internal/engine/load_request.go
@@ -292,6 +292,7 @@ func acquireUnderlayGroupScopes(group loadGroup, index int, rule *VersionRule, s
 		acquired, diagnostics := acquireInput(inputAcquisitionRequest{
 			input: contribution, role: sourceVersionContribution,
 			resolved:         selected[inputIndex],
+			withoutBase:      contribution.mainRelative != nil && contribution.filesystem == nil && selected[inputIndex] == nil,
 			directiveContext: rootDirectiveContextLayered, protectionRule: rule,
 		}, policy, state, tier)
 		for _, source := range acquired.sources {