[CI] Xcode 27 beta 5 Windows integration bots run macOS 26.3.1 instead of 26.4

## Summary

Windows Integration Test bot reservation repeatedly selects a macOS 26.3.1 host for Xcode 27 beta 5, but that Xcode build requires macOS 26.4. Provisioning retries four times and fails before Windows integration tests start.

- Stable signature: `windows-integration-xcode27-host-macos-too-old`
- Classification: CI infrastructure failure
- Distinct monitored PRs: 2
- Confirmed occurrences: 2
- First observed: 2026-08-12 15:14 UTC
- Latest observed: 2026-08-12 16:09 UTC

## Confirmed occurrences

- #26433, head `d0131c28fdd6e6107db5df5c7c13a9d613367e5e`
- [Build 14949555, Windows Integration Tests / Reserve macOS bot](https://devdiv.visualstudio.com/0bdbc590-a062-4c3f-b0f6-9383f67865ee/_build/results?buildId=14949555&view=logs&jobId=1483a13f-bcf1-57d8-b495-23590d1e6c0d)
- Host: macOS 26.3.1; Xcode 27 beta 5 requirement: macOS 26.4.
- Four provisioning task attempts failed. The overall build remains active.
- #26438, head `c12070bcb25ea8e62f8ed751289073f3bbb2d32b`
- [Build 14949997, Windows Integration Tests / Reserve macOS bot](https://devdiv.visualstudio.com/0bdbc590-a062-4c3f-b0f6-9383f67865ee/_build/results?buildId=14949997&view=logs&jobId=1483a13f-bcf1-57d8-b495-23590d1e6c0d)
- Host: macOS 26.3.1; Xcode 27 beta 5 requirement: macOS 26.4.
- Four provisioning task attempts failed. The overall build remains active.

## Reproduction and impact

The failure occurs before test execution while expanding and validating `Xcode_27_beta_5.xip`. Reserving an incompatible host deterministically fails the Windows Integration stage.

## Investigation performed

Azure build metadata, timelines, and provisioning task logs were inspected for both runs. Separate open/closed issue searches used the Xcode version, required/actual macOS versions, provisioning task, and Windows Integration component strings; no matching issue was found.

## Retry status and workaround

No retry has been submitted yet because both builds are still active. Under repository policy, the entire **Windows Integration Tests** stage must be rerun after terminal status, conflict/head/budget reconciliation, and confirmation that no equivalent retry is active. Infrastructure should reserve a macOS 26.4-or-newer host for Xcode 27 beta 5.

Start with the Azure build metadata, timelines, and provisioning task logs for the Windows Integration Tests stage, especially the Reserve macOS bot task. Confirm how Xcode_27_beta_5.xip host requirements are matched to available macOS hosts. Done means the stage reserves macOS 26.4 or newer and completes provisioning before the Windows integration tests run.

Written by the indexing model from the issue text.