Empty-body handling fixed "no share yet" but re-opening the share
sheet for a document that already had one still errored — confirmed
via a raw response capture that data is { shares: [...] }, a
one-element array, not the bare share object the docs show. Same
pattern as pins.list.
Added SharesInfoPayload (mirrors PinsListPayload), shareInfo now takes
.shares.first. createShare/updateShare are unaffected — the user's
earlier successful create-and-copy confirms those aren't wrapped this
way, only shares.info. Test rewritten with the exact captured payload.