BN01 fold2 finding (2c Low): collapsing the over-budget branch in
d24e5875b7 read `item["content"]` unguarded. A user message whose text
is measured only via `output_text` (no `content` key) reaches that
branch when it exceeds the budget and raised KeyError, aborting the
prune. Use `item.get("content")` so it falls through to the
non-truncatable path (keep nothing, budget reset) as before the
refactor. The typed-boundary parametrize gains a row for it.
4d1b2dcf65