[8.18](backport #7601) [packaging] proxy binary to be for the root dir of windows archive

[mergify]

What does this PR do?

This PR introduces a Windows-specific proxy binary (elastic-agent-archive-root.exe) that is placed at the root of the Elastic Agent .zip archive. The proxy acts as a thin wrapper that forwards execution to the actual agent binary located under the data/elastic-agent-{commit-sha} directory.

The proxy is built during the packaging step using a new Mage target (WindowsArchiveRootBinary), and replaces the duplicated agent binary that previously resided in the archive root due to lack of symlink support in .zip archives. This approach mimics the behavior seen on other platforms like Linux/macOS, where the root-level agent is a symlink into the versioned binary path.

This change avoids the need to duplicate the agent binary in the archive, reducing both the archive size and post-extraction disk footprint.

Why is it important?

The Windows .zip archive currently includes a full copy of the elastic-agent.exe binary at the root of the archive due to the lack of symlink support in the zip format. This duplication, increases the download size and disk footprint unnecessarily

Checklist

• I have read and understood the pull request guidelines of this project.
• My code follows the style guidelines of this project
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have made corresponding change to the default configuration files
• I have added tests that prove my fix is effective or that my feature works
• I have added an entry in ./changelog/fragments using the changelog tool
• I have added an integration test or an E2E test

Disruptive User Impact

There should be no disruptive user impact. The proxy binary is fully backward-compatible with existing workflows that invoke the elastic-agent.exe binary from the root of the archive on Windows. Users should not notice any difference in behavior.

How to test this PR locally

1. Package the windows archive

   PACKAGES=zip EXTERNAL=true PLATFORMS=windows/amd64 SNAPSHOT=true mage -v package
   

2. Unzip the resulting .zip file and verify that:

• The root elastic-agent.exe is a lightweight proxy (~2MB instead of 260MB+)
• The actual binary lives under data/elastic-agent-/elastic-agent.exe
• Running the root elastic-agent.exe launches the nested agent as expected

Related issues

• Closes [Windows] Shrink the disk footprint of the .zip package by including only one copy of elastic-agent.exe #7592

Manual Testing

1. DRA dry-run here and artifacts are produced successfully (link) (ty @pchila 🙏 )
2. With the windows artifact from the above I directly installed a fleet-managed and agent got installed fine and reported healthy
3. I installed a standalone agent at the version v8.17.4. Then again from the windows artifact of the above DRA I did an upgrade and this was successful

---

This is an automatic backport of pull request #7601 done by [Mergify](https://mergify.com).

[mergify]

Cherry-pick of 6b4b0dc has failed:

On branch mergify/bp/8.18/pr-7601
Your branch is up to date with 'origin/8.18'.

You are currently cherry-picking commit 6b4b0dc69.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Changes to be committed:
	modified:   magefile.go
	new file:   wrapper/windows/archive-proxy/go.mod
	new file:   wrapper/windows/archive-proxy/go.sum
	new file:   wrapper/windows/archive-proxy/main.go

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   dev-tools/packaging/packages.yml

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally

[elasticmachine]

Pinging @elastic/elastic-agent-control-plane (Team:Elastic-Agent-Control-Plane)

[elastic-sonarqube]

Quality Gate failed

Failed conditions
0.0% Coverage on New Code (required ≥ 40%)

See analysis details on SonarQube

[elasticmachine]

💛 Build succeeded, but was flaky

• Buildkite Build
• Commit: adb587d

Failed CI Steps

• Win2025:sudo:install-uninstall
• x86_64:sudo: fleet-endpoint-security

History

• 💔 Build #19370 failed 2249998

cc @pkoutsovasilis