Isolate user configuration discovery tests by platform

docs/roadmap/remediation.md

@@ -1,6 +1,6 @@
 # Configuration Discovery Review Findings
 
-Status: findings 1–2 complete; findings 3–5 remain open.
+Status: findings 1–3 complete; findings 4–5 remain open.
 
 Reviewed commit: `e50fee2`, including the discovery implementation commits after
 `424c897`. The review compared the implementation with the
@@ -101,7 +101,15 @@ still produce no records. Revise the existing nil-primary assertion accordingly.
 
 ## 3. Isolate User-Configuration Preset Tests Using The Platform's Go Convention
 
-Priority: P2. Status: open.
+Priority: P2. Status: complete.
+
+**Completed:** the environment-change test selects the environment variable used
+by Go on Windows, macOS/iOS, Plan 9, or other Unix hosts, and obtains both fixture
+bases through `os.UserConfigDir`. It remains nonparallel and restores the
+environment. The redundant relative-XDG failure assumption was removed; existing
+private-helper tests retain portable failure/short-circuit coverage. Focused
+tests and `./scripts/check.sh` passed on Linux. The macOS branch was checked
+against Go's helper implementation; no native macOS gate was added.
 
 **Location:** [discovery_load_test.go](../../internal/engine/discovery_load_test.go),
 `TestSearchSourceObservesUserConfigEnvironmentChanges`, lines 231–279.

internal/engine/discovery_load_test.go

@@ -326,21 +326,29 @@ func TestSearchSourceObservesFileChangesBetweenLoads(t *testing.T) {
 }
 
 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"))
+	setBase := func(directory string) string {
+		t.Helper()
+		switch runtime.GOOS {
+		case "windows":
+			t.Setenv("AppData", directory)
+		case "darwin", "ios":
+			t.Setenv("HOME", directory)
+		case "plan9":
+			t.Setenv("home", directory)
+		default:
+			t.Setenv("XDG_CONFIG_HOME", directory)
+		}
+		base, err := os.UserConfigDir()
+		if err != nil {
+			t.Fatal(err)
+		}
+		return base
 	}
 	type config struct {
 		Value string `yaml:"value"`
 	}
-	firstBase := os.Getenv("XDG_CONFIG_HOME")
-	if runtime.GOOS == "windows" {
-		firstBase = os.Getenv("APPDATA")
-	}
+	firstBase := setBase(filepath.Join(t.TempDir(), "first"))
 	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]{})
@@ -352,28 +360,11 @@ func TestSearchSourceObservesUserConfigEnvironmentChanges(t *testing.T) {
 	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)
-	}
+	secondBase := setBase(filepath.Join(t.TempDir(), "second"))
+	second := writeImportFile(t, secondBase, "app/app.yml", "value: second\n")
 	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) {