The spare covered only the pending round's tool results. The owning
assistant(tool_calls) row sits at spared.start - 1, below the lowered
prune boundary, so pass 3 (range(prune_boundary)) and pass 4's
_shrink_at still truncated its arguments: a pending 60 KB write_file
call came back as 456 chars next to its intact, unread result. The
model then reads its result beside a mangled copy of the call it just
made.
_spared_pending_tool_round now includes the owning assistant row, so
the boundary and _shrink_at skip it along with the results. That row
also counts toward the hard-share check, so the >20% escape hatch
(#61932) still applies to the whole round.
The existing pending-round test now gives the pending call >500-char
args and asserts the assistant's tool_calls survive unchanged (red
before, green after).
Co-authored-by: MongLong0214 <97578200+MongLong0214@users.noreply.github.com>
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