When partial inventories omitted node details, the root got an unknown
availability row and the differing manifest root digests appended a
second, changed content row, so one logical path was counted as both
changed and unknown. Fold the manifest content change into an existing
unknown or changed root row instead, keeping its dimensions, occurrence
and artifact identities, and citations; contradiction and presence rows
are left as they are.
Fixes#1844
Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>