weave

Weave every ply in the current desired set and bond them into one Seam.

All-or-nothing, and it leaks nothing (#1784). Unlike a live reconciliation — where one ply failing is absorbed and retried — a ply that cannot be woven here fails the whole weave: the caller gets no Seam at all, so onPlyFailure never sees it and, with the fixed-list constructor, there is no later list to retry from. Which is why the plies that did come up must not simply be dropped: this method is their only holder, and weave throwing leaves the caller no handle to close them with. So a failure closes them on the way out before rethrowing. The composite is precisely the type that must not leak a transport across a failed attach.