Strict memory budgets: batching wrappers need their own reservation

When adding batching to a job queue that runs under a strict memory budget (every allocation reserved against an account before it happens), it is easy to account the child jobs but forget the batch wrapper itself: the wrapper object and its reserved pointer array are new allocations that no child reservation covers. Reserve the wrapper separately before allocating, release it exactly once (including on abandon and failure paths), and do not reuse a per-job fixed-overhead convention for it. Also check whether a new minimum-capacity knob changes only the initial capacity or the whole growth schedule (doubling from the new minimum instead of the old floor); if the latter, document it as a separate factor and keep a control arm with the old behavior. Gate tests: flush under budget pressure, abandon a partial batch.