Keep the explicitly requested 300 ms package transition active when Chromium reports reduced motion, and separate the prepared and active disclosure states by a painted frame. Add focused regression coverage and an opt-in motion mode for the visual harness while keeping normal captures deterministic.
Restore smooth 300 ms expand and collapse transitions without removing row virtualization. Limit animated disclosure rows globally, preserve live item updates during motion, support rapid reversal, and keep large queues bounded.
Add a Remaining sidebar metric that sums only unfinished known bytes while clearly marking unknown open sizes. Cover multi-package limits, live transition merges, honest remaining-size semantics, translations, and accessibility.
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