Proposal: raise the minimum supported Xcode version to Xcode 26

We plan to raise this SDK’s minimum supported build toolchain to **Xcode 26**.

Apple now requires App Store Connect submissions to be [built with Xcode 26 or later and an iOS 26 SDK or later](https://developer.apple.com/news/upcoming-requirements/?id=04282026a). This lets us remove legacy Xcode/SDK compatibility code, older CI coverage, and workarounds that no longer serve App Store builds.

This is a request for concrete blockers before we make the change.

Please comment if you still need an older Xcode version, including:

- the oldest Xcode version you need;
- whether the app is distributed through the App Store, Enterprise/MDM, internal distribution, or another channel;
- why upgrading is blocked; and
- the specific SDK feature or integration that prevents the upgrade.

No files, tests, or implementation entry points are named. Start by reviewing the proposed Xcode 26 and iOS 26 SDK requirement, then identify any concrete older-Xcode blockers, including the oldest required version, distribution channel, upgrade constraint, and blocking SDK feature or integration; the issue is complete when those blockers are collected and the compatibility change is decided.

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