The salvaged lossless-history change rebuilt the carried head/tail from
canonical history, which undid _pressure_demote_tail's tool-result
shrinking and re-broke #61932 (an all-oversized tail could no longer
compress). Pruning no longer rewrites tool_calls, so the pruned copy's
arguments are already byte-identical to canonical history: assemble the
head and tail from the pruned copy, keeping tool-result demotions and
exact tool-call arguments at once. Docs updated to match.
f6ce8bb23b