diff --git a/docs/roadmap/implementation.md b/docs/roadmap/implementation.md
index d45dab4..b1d8595 100644
--- a/docs/roadmap/implementation.md
+++ b/docs/roadmap/implementation.md
@@ -1,6 +1,6 @@
 # Configuration Discovery Implementation Plan
 
-Status: in progress. Stages 1, 2, 3, 4, and 5 are complete.
+Status: in progress. Stages 1, 2, 3, 4, 5, and 6 are complete.
 
 Implement the target behavior in [the discovery roadmap](discovery.md). That
 document owns the selected conventions and OD-1 through OD-5; this plan owns the
@@ -322,7 +322,7 @@ Acceptance: shared absent-main behavior is complete for explicit `NoSource`.
 Run focused overlay/context/load tests, `go test -race ./internal/engine`, and
 the everyday check. Mark and commit.
 
-## Stage 6 — Integrate Search Resolution Into Engine Loading
+## Stage 6 — Integrate Search Resolution Into Engine Loading (Complete)
 
 1. Add a private discovery source kind/state to engine `Source` and have the
    engine `SearchConfig` constructor capture the validated description. Add
diff --git a/internal/engine/discovery.go b/internal/engine/discovery.go
index 4c6dd18..c4d63b3 100644
--- a/internal/engine/discovery.go
+++ b/internal/engine/discovery.go
@@ -34,6 +34,19 @@ type SearchOptions struct {
 	Required bool
 }
 
+// SearchConfig creates a source that selects the first matching host file when
+// consumed. Description and option errors are reported during loading.
+func SearchConfig(application string, search Search, supplied ...SearchOptions) Source {
+	captured := Search{entries: cloneSearchEntries(search.entries), issues: append([]string(nil), search.issues...)}
+	source := Source{kind: sourceSearch, search: &captured, searchApp: application}
+	if len(supplied) > 1 {
+		source.searchIssues = []string{"SearchConfig accepts at most one options value"}
+	} else if len(supplied) == 1 {
+		source.searchRequired = supplied[0].Required
+	}
+	return source
+}
+
 type filenameGroupKind uint8
 
 const (
diff --git a/internal/engine/discovery_load_test.go b/internal/engine/discovery_load_test.go
new file mode 100644
index 0000000..264189b
--- /dev/null
+++ b/internal/engine/discovery_load_test.go
@@ -0,0 +1,342 @@
+package engine
+
+import (
+	"errors"
+	"os"
+	"path/filepath"
+	"reflect"
+	"runtime"
+	"testing"
+)
+
+type discoveryLoadConfig struct {
+	Service struct {
+		Settings map[string]string `yaml:"settings"`
+	} `yaml:"service"`
+	Settings map[string]string `yaml:"settings"`
+	Value    string            `yaml:"value"`
+}
+
+func TestSearchLoadMatchesExplicitFileThroughImportsAndContext(t *testing.T) {
+	t.Parallel()
+
+	root := t.TempDir()
+	mainPath := writeImportFile(t, root, "app.yml", `configkit:
+  imports: [{path: fragments/extra.yml}]
+settings: {main: selected}
+`)
+	importPath := writeImportFile(t, root, "fragments/extra.yml", "settings: {imported: value}\n")
+	search := SearchConfig("app", SearchDirectory(root))
+	options := Options[discoveryLoadConfig]{
+		Imports: true, Filesystem: &FilesystemContext{Root: root}, destination: Keys("service"),
+	}
+	searched, err := testLoad(search, options)
+	if err != nil {
+		t.Fatal(err)
+	}
+	explicit, err := testLoad(File(mainPath), options)
+	if err != nil {
+		t.Fatal(err)
+	}
+	assertEquivalentDiscoveryLoads(t, searched.Config, searched.Inspection, explicit.Config, explicit.Inspection,
+		Keys("service", "settings", "main"), Keys("service", "settings", "imported"))
+
+	sources := searched.Sources()
+	if len(sources) != 2 || sources[0].Kind != SourceKindFile || sources[0].Path != canonicalTestPath(t, mainPath) || sources[1].Path != canonicalTestPath(t, importPath) {
+		t.Fatalf("searched source evidence = %#v", sources)
+	}
+}
+
+func TestSearchLayeredMainAndUnderlayMatchExplicitFiles(t *testing.T) {
+	t.Parallel()
+
+	root := t.TempDir()
+	mainPath := writeImportFile(t, root, "main.yml", "settings: {main: value}\n")
+	underlayPath := writeImportFile(t, root, "underlay/base.yml", `configkit:
+  imports: [{path: extra.yml}]
+settings: {underlay: value}
+`)
+	importPath := writeImportFile(t, root, "underlay/extra.yml", "settings: {imported: value}\n")
+	mainSearch := SearchConfig("", SearchDirectory(root, DirectorySearchOptions{Filenames: []FilenameGroup{CustomFilenames("main.yml")}}))
+	underlaySearch := SearchConfig("", SearchDirectory(filepath.Join(root, "underlay"), DirectorySearchOptions{Filenames: []FilenameGroup{CustomFilenames("base.yml")}}))
+	load := func(main, underlay Source) (*Loaded[discoveryLoadConfig], error) {
+		return LoadLayered(
+			Input{Source: main, Imports: true}, testSecretBinding(),
+			LayeredOptions[discoveryLoadConfig]{Underlays: []Underlay{{Inputs: []Input{{Source: underlay, Imports: true}}}}},
+		)
+	}
+	searched, err := load(mainSearch, underlaySearch)
+	if err != nil {
+		t.Fatal(err)
+	}
+	explicit, err := load(File(mainPath), File(underlayPath))
+	if err != nil {
+		t.Fatal(err)
+	}
+	assertEquivalentDiscoveryLoads(t, searched.Config, searched.Inspection, explicit.Config, explicit.Inspection,
+		Keys("settings", "main"), Keys("settings", "underlay"), Keys("settings", "imported"))
+
+	sources := searched.Inspection.Sources()
+	if len(sources) != 3 || sources[0].ID != "source-1" || sources[0].Layer != LayerBase || sources[1].ID != "source-2" || sources[1].Layer != LayerUnderlay || sources[2].Path != canonicalTestPath(t, importPath) || sources[2].UnderlayIndex != 1 {
+		t.Fatalf("layered search source evidence = %#v", sources)
+	}
+}
+
+func TestOptionalSearchExhaustionMatchesNoSource(t *testing.T) {
+	t.Parallel()
+
+	root := t.TempDir()
+	missing := filepath.Join(root, "missing.yml")
+	defaults := func() discoveryLoadConfig {
+		return discoveryLoadConfig{Value: "default"}
+	}
+	options := Options[discoveryLoadConfig]{
+		Definition: Definition[discoveryLoadConfig]{Defaults: defaults},
+		Imports:    true, Filesystem: &FilesystemContext{Root: root},
+	}
+	searched, err := testLoad(SearchConfig("", Paths(missing)), options)
+	if err != nil {
+		t.Fatal(err)
+	}
+	explicit, err := testLoad(NoSource(), options)
+	if err != nil {
+		t.Fatal(err)
+	}
+	assertEquivalentDiscoveryLoads(t, searched.Config, searched.Inspection, explicit.Config, explicit.Inspection, Keys("value"))
+	if len(searched.Sources()) != 0 {
+		t.Fatalf("optional exhausted search created sources: %#v", searched.Sources())
+	}
+}
+
+func TestSearchSelectedFileFailuresDoNotFallBack(t *testing.T) {
+	t.Parallel()
+
+	t.Run("malformed YAML", func(t *testing.T) {
+		first := writeImportFile(t, t.TempDir(), "first.yml", ": malformed\n")
+		writeImportFile(t, filepath.Dir(first), "later.yml", "value: valid\n")
+		loaded, err := testLoad[discoveryLoadConfig](SearchConfig("", Paths(first, filepath.Join(filepath.Dir(first), "later.yml"))), Options[discoveryLoadConfig]{})
+		if loaded != nil || err == nil {
+			t.Fatalf("malformed selected source = %#v, %v", loaded, err)
+		}
+	})
+
+	t.Run("version check", func(t *testing.T) {
+		root := t.TempDir()
+		first := writeImportFile(t, root, "first.yml", "version: rejected\n")
+		writeImportFile(t, root, "later.yml", "version: accepted\n")
+		var checked []string
+		loaded, err := testLoad[discoveryLoadConfig](SearchConfig("", Paths(first, filepath.Join(root, "later.yml"))), Options[discoveryLoadConfig]{
+			SourceVersionMode: sourceVersionModeIfPresent,
+			Definition: Definition[discoveryLoadConfig]{Version: &VersionRule{
+				Path: Keys("version"),
+				Check: func(version Version, _ *Validation) error {
+					checked = append(checked, version.Text)
+					if version.Text == "rejected" {
+						return errors.New("version rejected")
+					}
+					return nil
+				},
+			}},
+		})
+		if loaded != nil || err == nil || !reflect.DeepEqual(checked, []string{"rejected"}) {
+			t.Fatalf("version failure search = %#v, %v; checked %#v", loaded, err, checked)
+		}
+	})
+
+	t.Run("decode", func(t *testing.T) {
+		root := t.TempDir()
+		first := writeImportFile(t, root, "first.yml", "value: not-an-integer\n")
+		writeImportFile(t, root, "later.yml", "value: 3\n")
+		type config struct {
+			Value int `yaml:"value"`
+		}
+		loaded, err := testLoad[config](SearchConfig("", Paths(first, filepath.Join(root, "later.yml"))), Options[config]{})
+		if loaded != nil || err == nil {
+			t.Fatalf("decode failure search = %#v, %v", loaded, err)
+		}
+	})
+}
+
+func TestSearchValidationPrecedesCandidateProbing(t *testing.T) {
+	t.Parallel()
+
+	root := t.TempDir()
+	first := writeImportFile(t, root, "first.yml", "value: selected\n")
+	_, err := testLoad[discoveryLoadConfig](SearchConfig("", Searches(Paths(first), Paths(""))), Options[discoveryLoadConfig]{})
+	var loadErr *LoadError
+	if !errors.As(err, &loadErr) {
+		t.Fatalf("invalid later search error = %v, want *LoadError", err)
+	}
+	if len(loadErr.Diagnostics()) == 0 || loadErr.Diagnostics()[0].Code != CodeOptionsInvalid {
+		t.Fatalf("invalid later search component diagnostics = %#v", loadErr.Diagnostics())
+	}
+
+	malformed := writeImportFile(t, t.TempDir(), "main.yml", ": malformed\n")
+	loaded, err := LoadLayered(
+		Input{Source: SearchConfig("", Paths(malformed))}, testSecretBinding(),
+		LayeredOptions[discoveryLoadConfig]{Underlays: []Underlay{{Inputs: []Input{{Source: SearchConfig("", Paths(""))}}}}},
+	)
+	if loaded != nil || !errors.As(err, &loadErr) {
+		t.Fatalf("invalid later underlay search = %#v, %v", loaded, err)
+	}
+	for _, diagnostic := range loadErr.Diagnostics() {
+		if diagnostic.Code != CodeOptionsInvalid {
+			t.Fatalf("layered validation acquired main before rejecting underlay: %#v", loadErr.Diagnostics())
+		}
+	}
+}
+
+func TestSearchContextCompatibilityUsesSelectedOutcome(t *testing.T) {
+	t.Parallel()
+
+	root := t.TempDir()
+	first := writeImportFile(t, root, "first.yml", "value: first\n")
+	writeImportFile(t, root, "later.yml", "value: later\n")
+	search := SearchConfig("", Paths(first, filepath.Join(root, "later.yml")))
+	options := Options[discoveryLoadConfig]{Filesystem: &FilesystemContext{BaseDir: root, Root: root}}
+	_, err := testLoad[discoveryLoadConfig](search, options)
+	var loadErr *LoadError
+	if !errors.As(err, &loadErr) {
+		t.Fatalf("selected file with explicit base error = %v, want *LoadError", err)
+	}
+	if len(loadErr.Diagnostics()) == 0 || loadErr.Diagnostics()[0].Code != CodeOptionsInvalid {
+		t.Fatalf("selected file context diagnostics = %#v", loadErr.Diagnostics())
+	}
+}
+
+func TestSearchSourceObservesFileChangesBetweenLoads(t *testing.T) {
+	t.Parallel()
+
+	root := t.TempDir()
+	file := writeImportFile(t, root, "config.yml", "value: first\n")
+	source := SearchConfig("", SearchDirectory(root, DirectorySearchOptions{Filenames: []FilenameGroup{CustomFilenames("config.yml")}}))
+	load := func() string {
+		loaded, err := testLoad[discoveryLoadConfig](source, Options[discoveryLoadConfig]{})
+		if err != nil {
+			t.Fatal(err)
+		}
+		return loaded.Config.Value
+	}
+	if value := load(); value != "first" {
+		t.Fatalf("first search value = %q", value)
+	}
+	if err := os.WriteFile(file, []byte("value: second\n"), 0o600); err != nil {
+		t.Fatal(err)
+	}
+	if value := load(); value != "second" {
+		t.Fatalf("updated search value = %q", value)
+	}
+}
+
+func TestSearchSourceObservesUserConfigEnvironmentChanges(t *testing.T) {
+	if runtime.GOOS == "windows" {
+		t.Setenv("APPDATA", filepath.Join(t.TempDir(), "first"))
+	} else {
+		t.Setenv("XDG_CONFIG_HOME", filepath.Join(t.TempDir(), "first"))
+	}
+	type config struct {
+		Value string `yaml:"value"`
+	}
+	firstBase := os.Getenv("XDG_CONFIG_HOME")
+	if runtime.GOOS == "windows" {
+		firstBase = os.Getenv("APPDATA")
+	}
+	first := writeImportFile(t, firstBase, "app/app.yml", "value: first\n")
+	secondBase := filepath.Join(t.TempDir(), "second")
+	second := writeImportFile(t, secondBase, "app/app.yml", "value: second\n")
+	source := SearchConfig("app", UserConfigDirectory())
+	load := func() string {
+		loaded, err := testLoad[config](source, Options[config]{})
+		if err != nil {
+			t.Fatal(err)
+		}
+		return loaded.Config.Value
+	}
+	if value := load(); value != "first" {
+		t.Fatalf("first user-config search value = %q (%s)", value, first)
+	}
+	if runtime.GOOS == "windows" {
+		t.Setenv("APPDATA", secondBase)
+	} else {
+		t.Setenv("XDG_CONFIG_HOME", secondBase)
+	}
+	if value := load(); value != "second" {
+		t.Fatalf("updated user-config search value = %q (%s)", value, second)
+	}
+
+	// A reached dynamic base failure is terminal, but an earlier match must
+	// prevent the invalid environment value from being resolved at all.
+	direct := writeImportFile(t, t.TempDir(), "direct.yml", "value: direct\n")
+	if runtime.GOOS == "windows" {
+		t.Setenv("APPDATA", "relative")
+	} else {
+		t.Setenv("XDG_CONFIG_HOME", "relative")
+	}
+	early := SearchConfig("app", Searches(Paths(direct), UserConfigDirectory()))
+	loaded, err := testLoad[config](early, Options[config]{})
+	if err != nil || loaded.Config.Value != "direct" {
+		t.Fatalf("early match with unavailable later base = %#v, %v", loaded, err)
+	}
+}
+
+func TestSearchSourceObservesWorkingDirectoryChanges(t *testing.T) {
+	original, err := os.Getwd()
+	if err != nil {
+		t.Fatal(err)
+	}
+	t.Cleanup(func() {
+		if err := os.Chdir(original); err != nil {
+			t.Errorf("restore working directory: %v", err)
+		}
+	})
+	firstDir := t.TempDir()
+	secondDir := t.TempDir()
+	writeImportFile(t, firstDir, "app.yml", "value: first\n")
+	writeImportFile(t, secondDir, "app.yml", "value: second\n")
+	source := SearchConfig("app", WorkingDirectory())
+	load := func() string {
+		loaded, err := testLoad[discoveryLoadConfig](source, Options[discoveryLoadConfig]{})
+		if err != nil {
+			t.Fatal(err)
+		}
+		return loaded.Config.Value
+	}
+	if err := os.Chdir(firstDir); err != nil {
+		t.Fatal(err)
+	}
+	if value := load(); value != "first" {
+		t.Fatalf("first working-directory search value = %q", value)
+	}
+	if err := os.Chdir(secondDir); err != nil {
+		t.Fatal(err)
+	}
+	if value := load(); value != "second" {
+		t.Fatalf("updated working-directory search value = %q", value)
+	}
+}
+
+func assertEquivalentDiscoveryLoads[T any](t *testing.T, leftConfig T, left *Inspection, rightConfig T, right *Inspection, presencePaths ...Path) {
+	t.Helper()
+	if !reflect.DeepEqual(leftConfig, rightConfig) {
+		t.Fatalf("search config %#v differs from explicit file config %#v", leftConfig, rightConfig)
+	}
+	leftSources, rightSources := left.Sources(), right.Sources()
+	if !reflect.DeepEqual(leftSources, rightSources) {
+		t.Fatalf("search sources %#v differ from explicit file sources %#v", leftSources, rightSources)
+	}
+	leftMetadata, rightMetadata := left.Metadata(), right.Metadata()
+	for _, path := range presencePaths {
+		leftInfo, leftPresent := leftMetadata.Lookup(path)
+		rightInfo, rightPresent := rightMetadata.Lookup(path)
+		if leftPresent != rightPresent || !reflect.DeepEqual(leftInfo, rightInfo) {
+			t.Fatalf("search metadata at %s = %#v, %v; explicit metadata = %#v, %v", path.String(), leftInfo, leftPresent, rightInfo, rightPresent)
+		}
+	}
+	for _, source := range leftSources {
+		leftContext, leftOK := left.SourceContext(source.ID)
+		rightContext, rightOK := right.SourceContext(source.ID)
+		if leftOK != rightOK || leftContext.BaseDir != rightContext.BaseDir || (leftContext.FS != nil) != (rightContext.FS != nil) {
+			t.Fatalf("search context for %s = %#v, %v; explicit context = %#v, %v", source.ID, leftContext, leftOK, rightContext, rightOK)
+		}
+	}
+}
diff --git a/internal/engine/filesystem.go b/internal/engine/filesystem.go
index 30a671a..4067ed2 100644
--- a/internal/engine/filesystem.go
+++ b/internal/engine/filesystem.go
@@ -77,13 +77,9 @@ func validateAbsentHostFilesystemContext(context *FilesystemContext) *Diagnostic
 func filesystemOptionDiagnostics(source Source, context *FilesystemContext) []Diagnostic {
 	switch source.kind {
 	case sourceNone:
-		if context.FS != nil {
-			if context.FS.namespace == nil || nilFilesystem(context.FS.namespace.filesystem) || context.BaseDir == "" || context.Root == "" || !fs.ValidPath(context.BaseDir) || !fs.ValidPath(context.Root) {
-				return []Diagnostic{optionDiagnostic(CodeOptionsInvalid, "native filesystem context requires a namespace, base, and root directory")}
-			}
-		} else if context.Root == "" || !filepath.IsAbs(context.Root) || context.BaseDir != "" && !filepath.IsAbs(context.BaseDir) {
-			return []Diagnostic{optionDiagnostic(CodeOptionsInvalid, "absent-input filesystem root and base directories must be absolute host paths")}
-		}
+		return absentFilesystemOptionDiagnostics(context)
+	case sourceSearch:
+		return absentFilesystemOptionDiagnostics(context)
 	case sourceFile:
 		if context.FS != nil {
 			return []Diagnostic{optionDiagnostic(CodeOptionsInvalid, "host file sources cannot use a native filesystem context")}
@@ -116,6 +112,17 @@ func filesystemOptionDiagnostics(source Source, context *FilesystemContext) []Di
 	return nil
 }
 
+func absentFilesystemOptionDiagnostics(context *FilesystemContext) []Diagnostic {
+	if context.FS != nil {
+		if context.FS.namespace == nil || nilFilesystem(context.FS.namespace.filesystem) || context.BaseDir == "" || context.Root == "" || !fs.ValidPath(context.BaseDir) || !fs.ValidPath(context.Root) {
+			return []Diagnostic{optionDiagnostic(CodeOptionsInvalid, "native filesystem context requires a namespace, base, and root directory")}
+		}
+	} else if context.Root == "" || !filepath.IsAbs(context.Root) || context.BaseDir != "" && !filepath.IsAbs(context.BaseDir) {
+		return []Diagnostic{optionDiagnostic(CodeOptionsInvalid, "absent-input filesystem root and base directories must be absolute host paths")}
+	}
+	return nil
+}
+
 func nativeContext(source Source, context *FilesystemContext) bool {
 	return source.kind == sourceFilesystem || context != nil && context.FS != nil
 }
diff --git a/internal/engine/load.go b/internal/engine/load.go
index a0192d6..7fccf49 100644
--- a/internal/engine/load.go
+++ b/internal/engine/load.go
@@ -202,6 +202,7 @@ func executeLoadRequest[T any](request loadRequest[T], secrets SecretBinding, lo
 	}
 	accumulator.versionState = versionState
 	input, diagnostics := assembleBaseInputTrackedWithVersion(request.main.source, mainOptions, request.main.destination, accounting, nil, nil, versionState)
+	request.main.source = input.source
 	accumulator.sources = input.sources
 	accumulator.add(versionState.diagnostics...)
 	reportedVersionDiagnostics := len(versionState.diagnostics)
diff --git a/internal/engine/load_input.go b/internal/engine/load_input.go
index a421c9c..a9c3ebc 100644
--- a/internal/engine/load_input.go
+++ b/internal/engine/load_input.go
@@ -8,6 +8,7 @@ import (
 
 // assembledInput is the source/document handoff across schema and version checks.
 type assembledInput struct {
+	source       Source
 	parsed       parsedSource
 	document     *document.Node
 	composition  *composedDocument
@@ -101,20 +102,36 @@ func assembleBaseInputTrackedWithVersion[T any](source Source, options Options[T
 }
 
 func assembleBaseInputTrackedForRole[T any](source Source, options Options[T], destination Path, accounting *importAccounting, visited map[resourceIdentity]importRoute, hostToken *namespaceToken, versionState *sourceVersionState, role sourceVersionRole) (assembledInput, []Diagnostic) {
+	selectedSource := source
+	if source.kind == sourceSearch {
+		resolved, diagnostics := resolveSearchSource(source, source.search, source.searchApp, source.searchRequired, defaultDiscoveryDirectoryHelpers(), defaultDiscoveryHostProbe())
+		if len(diagnostics) != 0 {
+			return assembledInput{source: source, versionState: versionState, accounting: accounting}, diagnostics
+		}
+		selectedSource = resolved
+		if options.Filesystem != nil {
+			if diagnostics := filesystemOptionDiagnostics(selectedSource, options.Filesystem); len(diagnostics) != 0 {
+				return assembledInput{source: selectedSource, versionState: versionState, accounting: accounting}, diagnostics
+			}
+		}
+		if selectedSource.kind == sourceNone && activeOverlay(options.Overlay) && options.Filesystem == nil {
+			return assembledInput{source: selectedSource, versionState: versionState, accounting: accounting}, []Diagnostic{optionDiagnostic(CodeOptionsInvalid, "NoSource overlays require explicit filesystem context")}
+		}
+	}
 	limits := defaultImportLimits()
 	parseLimits := defaultParseLimits()
 	parseLimits.source.remaining = limits.bytes - accounting.bytes
-	parsed, diagnostics := parseSource(source, "source-"+strconv.Itoa(accounting.sources+1), parseLimits)
+	parsed, diagnostics := parseSource(selectedSource, "source-"+strconv.Itoa(accounting.sources+1), parseLimits)
 	if parsed.source != nil {
 		parsed.source.Destination = destination.clone()
 		parsed.source.placementMode = options.placementMode
 	}
-	input := assembledInput{parsed: parsed, document: parsed.document, sources: sourceInfos(parsed.source), versionState: versionState, accounting: accounting}
+	input := assembledInput{source: selectedSource, parsed: parsed, document: parsed.document, sources: sourceInfos(parsed.source), versionState: versionState, accounting: accounting}
 	if len(diagnostics) != 0 {
 		input.sources = sourceInfos(parsed.source)
 		// Mapping value issues already identify application content. Other early
 		// failures describe source syntax or access, not a placed value.
-		if source.kind == sourceMapping && source.mapIssue != nil && len(destination.segments) != 0 {
+		if selectedSource.kind == sourceMapping && selectedSource.mapIssue != nil && len(destination.segments) != 0 {
 			for index := range diagnostics {
 				relative := diagnostics[index].Path
 				segments := clonePathSegments(destination.segments, len(relative.segments))
@@ -200,11 +217,11 @@ func assembleBaseInputTrackedForRole[T any](source Source, options Options[T], d
 			versionState.mainProcessing = &processed
 		}
 	}
-	if options.Imports && source.kind != sourceNone {
+	if options.Imports && selectedSource.kind != sourceNone {
 		if options.deferAssembly {
-			input.composition, input.sources, diagnostics = loadImportedDocumentsTrackedWithProcessingDeferred(source, options.Filesystem, parsed, destination, options.Definition.Version, limits, accounting, visited, hostToken, versionState, versionProcessing, options.sequencePolicy, true)
+			input.composition, input.sources, diagnostics = loadImportedDocumentsTrackedWithProcessingDeferred(selectedSource, options.Filesystem, parsed, destination, options.Definition.Version, limits, accounting, visited, hostToken, versionState, versionProcessing, options.sequencePolicy, true)
 		} else {
-			input.composition, input.sources, diagnostics = loadImportedDocumentsTrackedWithProcessing(source, options.Filesystem, parsed, destination, options.Definition.Version, limits, accounting, visited, hostToken, versionState, versionProcessing, options.sequencePolicy)
+			input.composition, input.sources, diagnostics = loadImportedDocumentsTrackedWithProcessing(selectedSource, options.Filesystem, parsed, destination, options.Definition.Version, limits, accounting, visited, hostToken, versionState, versionProcessing, options.sequencePolicy)
 		}
 		if len(diagnostics) != 0 {
 			return input, diagnostics
@@ -218,8 +235,8 @@ func assembleBaseInputTrackedForRole[T any](source Source, options Options[T], d
 		if versionProcessing != nil {
 			input.document = versionProcessing.payload
 		}
-		if options.Filesystem != nil && (source.kind == sourceNone || !activeOverlay(options.Overlay)) {
-			if diagnostic := validateFilesystemContext(source, options.Filesystem, parsed); diagnostic != nil {
+		if options.Filesystem != nil && (selectedSource.kind == sourceNone || !activeOverlay(options.Overlay)) {
+			if diagnostic := validateFilesystemContext(selectedSource, options.Filesystem, parsed); diagnostic != nil {
 				return input, []Diagnostic{*diagnostic}
 			}
 		}
@@ -251,7 +268,7 @@ func assembleBaseInputTrackedForRole[T any](source Source, options Options[T], d
 		if accounting.sources+1 > limits.sources || accounting.bytes+parsed.bytes > limits.bytes || accounting.nodes+rawNodes+placementNodes > limits.nodes {
 			return input, []Diagnostic{sourceDiagnostic(CodeSourceLimitExceeded, parsed.source.ID, "configuration exceeds the aggregate input limit")}
 		}
-		if diagnostic := registerAcquiredSource(source, options.Filesystem, parsed.source, visited, hostToken); diagnostic != nil {
+		if diagnostic := registerAcquiredSource(selectedSource, options.Filesystem, parsed.source, visited, hostToken); diagnostic != nil {
 			return input, []Diagnostic{*diagnostic}
 		}
 		accounting.sources++
@@ -259,7 +276,7 @@ func assembleBaseInputTrackedForRole[T any](source Source, options Options[T], d
 		accounting.nodes += rawNodes + placementNodes
 	}
 	if !activeOverlay(options.Overlay) || options.Imports {
-		contexts, diagnostic := contextsForAcquiredSources(source, options.Filesystem, parsed.source, input.sources)
+		contexts, diagnostic := contextsForAcquiredSources(selectedSource, options.Filesystem, parsed.source, input.sources)
 		if diagnostic != nil {
 			return input, []Diagnostic{*diagnostic}
 		}
diff --git a/internal/engine/options.go b/internal/engine/options.go
index 802be28..4b833a9 100644
--- a/internal/engine/options.go
+++ b/internal/engine/options.go
@@ -31,6 +31,16 @@ func selectOptions[T any](source Source, supplied []Options[T]) (Options[T], []D
 	if options.Filesystem != nil {
 		diagnostics = append(diagnostics, filesystemOptionDiagnostics(source, options.Filesystem)...)
 	}
+	if source.kind == sourceSearch {
+		for _, issue := range source.searchIssues {
+			diagnostics = append(diagnostics, optionDiagnostic(CodeOptionsInvalid, issue))
+		}
+		if source.search == nil {
+			diagnostics = append(diagnostics, optionDiagnostic(CodeOptionsInvalid, "configuration search is invalid"))
+		} else {
+			diagnostics = append(diagnostics, validateSearch(*source.search, source.searchApp)...)
+		}
+	}
 	if source.kind == sourceNone && activeOverlay(options.Overlay) && options.Filesystem == nil {
 		diagnostics = append(diagnostics, optionDiagnostic(CodeOptionsInvalid, "NoSource overlays require explicit filesystem context"))
 	}
diff --git a/internal/engine/source.go b/internal/engine/source.go
index 5b7a89d..e66f57c 100644
--- a/internal/engine/source.go
+++ b/internal/engine/source.go
@@ -21,17 +21,21 @@ const (
 // Source is an opaque configuration input. Construct sources with File,
 // Filesystem.File, Bytes, Reader, or NoSource; the zero value is invalid.
 type Source struct {
-	kind      sourceKind
-	path      string
-	label     string
-	namespace *nativeNamespace
-	data      []byte
-	reader    *readerSource
-	mapping   *document.Node
-	mapIssue  *valueIssue
-	mapBytes  int64
-	mapNodes  int
-	createErr sourceCreationError
+	kind           sourceKind
+	path           string
+	label          string
+	namespace      *nativeNamespace
+	data           []byte
+	reader         *readerSource
+	mapping        *document.Node
+	mapIssue       *valueIssue
+	mapBytes       int64
+	mapNodes       int
+	createErr      sourceCreationError
+	search         *Search
+	searchApp      string
+	searchRequired bool
+	searchIssues   []string
 }
 
 type sourceKind uint8
@@ -44,6 +48,7 @@ const (
 	sourceReader
 	sourceMapping
 	sourceNone
+	sourceSearch
 )
 
 type sourceCreationError uint8