After restart, reservedTargetPaths (in-memory) was empty so claimTargetPath
could not distinguish between "file belongs to this item" and "file belongs
to another item". The naive fix (allow overwrite if unclaimed) would have
risked overwriting completed files from other items.
Proper fix: restore reservedTargetPaths from persisted session data on init.
This way each item's targetPath is correctly claimed, and claimTargetPath
can safely reuse the item's own file while protecting other items' files.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
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