[denialhaag]

Description

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Keep the input DD and its owned reference unchanged when global-phase application fails to allocate. Register the replacement root before changing the caller's edge.

Frontports the global-phase fix from #2826.

AI notice

This PR and its contents were created with the assistance of GPT-6 Astra via Codex.

Checklist

• The pull request only contains commits that are focused and relevant to this change.
• I have added appropriate tests that cover the new/changed functionality.
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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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[denialhaag]

Not sure if this test addition is really needed...