Validate search filesystem context after selection

docs/roadmap/remediation.md

@@ -1,6 +1,6 @@
 # Configuration Discovery Review Findings
 
-Status: five open findings. Implementation has not been changed by these reviews.
+Status: finding 1 complete; findings 2–5 remain open.
 
 Reviewed commit: `e50fee2`, including the discovery implementation commits after
 `424c897`. The review compared the implementation with the
@@ -10,7 +10,13 @@ configuration and architecture contracts.
 
 ## 1. Defer Absence-Only Context Requirements Until The Search Outcome Is Known
 
-Priority: P2. Status: open.
+Priority: P2. Status: complete.
+
+**Completed:** search prevalidation now defers absence-only root requirements
+until selection. Ordinary, layered-main, and underlay regression cases compare
+searched files with explicit files under an empty context and retain errors for
+absent inputs. The regression failed before the fix. Focused context/absence
+tests and `./scripts/check.sh` passed with Go 1.26.10 on Linux.
 
 **Location:** [filesystem.go](../../internal/engine/filesystem.go), lines 77–123,
 and the outcome-specific validation in

internal/engine/discovery_load_test.go

@@ -204,6 +204,53 @@ func TestSearchContextCompatibilityUsesSelectedOutcome(t *testing.T) {
 	}
 }
 
+func TestSearchEmptyContextUsesSelectedOutcome(t *testing.T) {
+	t.Parallel()
+
+	root := t.TempDir()
+	selected := writeImportFile(t, root, "selected.yml", "value: selected\n")
+	missing := filepath.Join(root, "missing.yml")
+	context := &FilesystemContext{}
+	for _, entry := range []struct {
+		name string
+		load func(Source) (*Loaded[discoveryLoadConfig], error)
+	}{
+		{"ordinary", func(source Source) (*Loaded[discoveryLoadConfig], error) {
+			return Load(source, testSecretBinding(), Options[discoveryLoadConfig]{Imports: true, Filesystem: context})
+		}},
+		{"layered main", func(source Source) (*Loaded[discoveryLoadConfig], error) {
+			return LoadLayered(Input{Source: source, Imports: true, Filesystem: context}, testSecretBinding(), LayeredOptions[discoveryLoadConfig]{})
+		}},
+		{"underlay", func(source Source) (*Loaded[discoveryLoadConfig], error) {
+			return LoadLayered(Input{Source: NoSource()}, testSecretBinding(), LayeredOptions[discoveryLoadConfig]{
+				Underlays: []Underlay{{Inputs: []Input{{Source: source, Imports: true, Filesystem: context}}}},
+			})
+		}},
+	} {
+		t.Run(entry.name, func(t *testing.T) {
+			explicit, err := entry.load(File(selected))
+			if err != nil {
+				t.Fatal(err)
+			}
+			searched, err := entry.load(SearchConfig("", Paths(missing, selected)))
+			if err != nil {
+				t.Fatal(err)
+			}
+			assertEquivalentDiscoveryLoads(t, searched.Config, searched.Inspection, explicit.Config, explicit.Inspection, Keys("value"))
+			if searched.Config.Value != "selected" {
+				t.Fatalf("selected value = %q", searched.Config.Value)
+			}
+			for _, source := range []Source{NoSource(), SearchConfig("", Paths(missing))} {
+				result, err := entry.load(source)
+				var failure *LoadError
+				if result != nil || !errors.As(err, &failure) || len(failure.Diagnostics()) != 1 || failure.Diagnostics()[0].Code != CodeOptionsInvalid {
+					t.Fatalf("absent input with empty context = %#v, %v", result, err)
+				}
+			}
+		})
+	}
+}
+
 func TestSearchSourceObservesFileChangesBetweenLoads(t *testing.T) {
 	t.Parallel()
 

internal/engine/filesystem.go

@@ -79,7 +79,14 @@ func filesystemOptionDiagnostics(source Source, context *FilesystemContext) []Di
 	case sourceNone:
 		return absentFilesystemOptionDiagnostics(context)
 	case sourceSearch:
-		return absentFilesystemOptionDiagnostics(context)
+		if context.FS != nil {
+			return absentFilesystemOptionDiagnostics(context)
+		}
+		// A selected host file can derive its root; absence requires an
+		// explicit root. Check that compatibility only after selection.
+		if context.BaseDir != "" && !filepath.IsAbs(context.BaseDir) {
+			return []Diagnostic{optionDiagnostic(CodeOptionsInvalid, "filesystem base directory must be an absolute host path")}
+		}
 	case sourceFile:
 		if context.FS != nil {
 			return []Diagnostic{optionDiagnostic(CodeOptionsInvalid, "host file sources cannot use a native filesystem context")}