Agent customization migration view jitters and becomes temporarily empty while session runs

Insiders:

https://github.com/user-attachments/assets/a98d75bf-57f4-4272-a7d1-45b857909243

Steps to Reproduce:

1. Start a new Agent Window session, or continue an existing session.
2. When the warning appears that customizations need to be updated, click it to open the customization migration view.
3. Leave the migration view open while the agent continues running and the underlying harness reports progress or other updates.

**Actual behavior**

The migration view repeatedly re-renders or refreshes even though its relevant content has not changed. Its content visibly jitters, and the view can become completely empty for several seconds before appearing again. This continues as the agent reports new information and causes severe lag across the UI.

**Expected behavior**

The migration view should remain stable and responsive while the agent runs. Unrelated session or harness updates should not clear or re-render the migration content unless data used by that view actually changes.

**Additional context**

This appears correlated with ongoing agent/harness updates rather than changes to migration state. The repeated updates make it difficult to read or interact with the migration view.