Create parent directories only after the containment check in InstallHelper.TryExtractToDirectory

src/code/InstallHelper.cs の InstallHelper.TryExtractToDirectory から始め、ディレクトリ作成と containment チェックのロジック周辺を確認します。entry.FullName がどのように destinationPath になるかを追跡し、ディレクトリやファイルに対する副作用が発生する前に containment がチェックされていることを検証します。完了条件は、containment によって拒否されたエントリがディレクトリを一切残さず、有効なエントリは引き続き通常どおり展開されることです。

Summary of the new feature / enhancement

During package extraction, entry-derived parent directories are created before the path-containment decision runs. An entry whose file write the containment check would reject can still leave empty directories outside the extraction root (directory-only effect — no file content is written outside). As a user, I want each entry's extraction side effects to be all-or-nothing, so a malformed package cannot leave stray directories anywhere on disk.

Proposed technical implementation details

In src/code/InstallHelper.cs, TryExtractToDirectory (~L1299 on current main):

• For entries containing a path separator, Directory.CreateDirectory(Path.Combine(extractPath, parentDirs)) runs first (~L1372-1377), using the raw entry prefix.
• Only afterwards is destinationPath = Path.GetFullPath(Path.Combine(extractPath, entry.FullName)) computed and the StartsWith(extractPath) containment verified (~L1381-1386) — and that check gates only the ExtractToFile call (~L1388).

So a package containing an entry such as ../../../../empty/dir/x (this loop is reached on installs from HTTP repositories, which do not go through a BCL extraction up front) creates empty/dir relative to the extraction temp directory as empty directories, and then the file write is skipped by the containment check.

Suggested reordering, so containment gates every side effect:

1. Compute destinationPath = Path.GetFullPath(Path.Combine(extractPath, entry.FullName)) first.
2. Verify containment of destinationPath under extractPath.
3. Only then create Path.GetDirectoryName(destinationPath) and call ExtractToFile.
4. Skip entries that fail containment entirely — no partial side effects.

This also makes directory creation consistent with the resolved path rather than the raw entry string.