Changing any required_role cell saves the policy and re-renders the units
list to refresh the attribution chips, but the re-render rebuilt every
<details> closed — collapsing the accordion the admin was actively
editing (m, 2026-05-08 11:19).
Capture the set of open data-unit-ids before innerHTML overwrites them,
then re-apply the open attribute on the rendered nodes for those ids.
Adds data-unit-id to the <details> as the stable identity. No behavior
change for first render or for units the admin hadn't expanded.
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