CI fix windows integration test failures

[julian-hj]

Fix ShrinkRootPartition to reliably free space on stemcell 2019.99

On stemcell 2019.99 the gap between SizeMin (~29.05 GB) and the partition size (~30 GB) is only ~950 MB. The previous approach used SizeMin + 1 GB as the target, which exceeded SizeMax (= CurrentSize) and caused Resize-Partition to fail with "Size Not Supported". A later attempt used SizeMax - 10 GB, which fell below SizeMin and caused Resize-Partition to silently return exit code 0 without making any change (LargestFreeExtent remained 0).

Fix by shrinking 200 MB from the current partition size:

• Uses (Get-Partition).Size (current size) instead of SizeMax, so we always shrink even when there is adjacent unallocated space.
• 200 MB is well within the achievable range (~950 MB gap) and well above the agent's 1 MB minimum for creating an ephemeral partition.
• Small amount means minimal data movement and fast completion.

Also remove the agent-windows-large-root-disk.yml ops file added as a workaround: the AWS CPI ignores root_disk in instance-group-level cloud_properties, so the disk remained at 30 GB regardless. The ops file is no longer needed with the corrected shrink strategy.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: ASSERTIVE

Plan: Pro

Run ID: 4a4bf249-9e70-453f-8a61-d95b1c6fb330

📥 Commits

Reviewing files that changed from the base of the PR and between e1ffdfc and 0a022ce.

📒 Files selected for processing (3)

• ci/pipeline.yml
• integration/assets/agent-windows-large-root-disk.yml
• integration/windows/environment_test.go

💤 Files with no reviewable changes (1)

• integration/assets/agent-windows-large-root-disk.yml

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Walkthrough

This PR removes the 100GB disk override for Windows integration test deployments. The agent-windows-large-root-disk.yml ops file is deleted and its reference is removed from the CI pipeline configuration. The Windows test code is updated to shrink the C: partition by a smaller fixed 200 MB amount computed from the current partition size, replacing the previous 10 GB shrink logic that was tied to the maximum supported partition size.

Suggested reviewers

• aramprice

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title accurately summarizes the main change: fixing Windows integration test failures in the CI pipeline, which is the core objective of the pull request.
Description check	✅ Passed	The description comprehensively explains the root cause of the test failures, the solution implemented, and the rationale for removing the ops file workaround.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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✨ Finishing Touches

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• Create stacked PR
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🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch fix-windows-integration-flakes-re-redux

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