fix: harden thothctl Windows safe I/O

tools/thothctl/internal/testsupport/symlink.go

@@ -0,0 +1,19 @@
+// Package testsupport provides portable helpers shared by thothctl tests.
+package testsupport
+
+import (
+	"os"
+	"testing"
+)
+
+// SymlinkOrSkip creates a symlink or skips only when Windows reports that symlink privilege is
+// unavailable. All other failures remain test failures.
+func SymlinkOrSkip(t testing.TB, target, link string) {
+	t.Helper()
+	if err := os.Symlink(target, link); err != nil {
+		if isSymlinkPrivilegeUnavailable(err) {
+			t.Skip("Windows symlink privilege is unavailable")
+		}
+		t.Fatal(err)
+	}
+}

tools/thothctl/internal/testsupport/symlink_nonwindows.go

@@ -0,0 +1,7 @@
+//go:build !windows
+
+package testsupport
+
+func isSymlinkPrivilegeUnavailable(_ error) bool {
+	return false
+}

tools/thothctl/internal/testsupport/symlink_test.go

@@ -0,0 +1,12 @@
+package testsupport
+
+import (
+	"errors"
+	"testing"
+)
+
+func TestSymlinkPrivilegeUnavailableDoesNotMatchUnrelatedErrors(t *testing.T) {
+	if isSymlinkPrivilegeUnavailable(errors.New("unrelated symlink failure")) {
+		t.Fatal("unrelated symlink failure was classified as a missing Windows privilege")
+	}
+}

tools/thothctl/internal/testsupport/symlink_windows.go

@@ -0,0 +1,14 @@
+//go:build windows
+
+package testsupport
+
+import (
+	"errors"
+	"os"
+
+	"golang.org/x/sys/windows"
+)
+
+func isSymlinkPrivilegeUnavailable(err error) bool {
+	return errors.Is(err, os.ErrPermission) || errors.Is(err, windows.ERROR_PRIVILEGE_NOT_HELD)
+}

tools/thothctl/internal/testsupport/symlink_windows_test.go

@@ -0,0 +1,38 @@
+//go:build windows
+
+package testsupport
+
+import (
+	"os"
+	"testing"
+
+	"golang.org/x/sys/windows"
+)
+
+func TestSymlinkPrivilegeUnavailableRecognizesOnlyWindowsPrivilegeErrors(t *testing.T) {
+	for name, err := range map[string]error{
+		"permission": os.ErrPermission,
+		"privilege not held": &os.LinkError{
+			Op:  "symlink",
+			Old: "target",
+			New: "link",
+			Err: windows.ERROR_PRIVILEGE_NOT_HELD,
+		},
+	} {
+		t.Run(name, func(t *testing.T) {
+			if !isSymlinkPrivilegeUnavailable(err) {
+				t.Fatalf("isSymlinkPrivilegeUnavailable(%v) = false, want true", err)
+			}
+		})
+	}
+
+	unrelated := &os.LinkError{
+		Op:  "symlink",
+		Old: "target",
+		New: "link",
+		Err: windows.ERROR_FILENAME_EXCED_RANGE,
+	}
+	if isSymlinkPrivilegeUnavailable(unrelated) {
+		t.Fatal("unrelated Windows symlink failure was classified as a missing privilege")
+	}
+}