Regression test for the exact issue #61932 report: head + an 8-message
protected tail made exclusively of oversized tool pairs. Pre-fix,
compress_start >= compress_end made compress() a pure no-op and the
retry loop ended in 'Cannot compress further'; post-fix the Phase-1
pressure demotion reclaims the tail in one pass while preserving
tool_call/tool_result pairing.
After multiple in-place compactions, short tool-heavy sessions can leave
nearly every remaining message inside protect_last_n while those messages
are huge completed file/tool outputs. The middle compress window then
makes no material token progress and the turn dies with
"Cannot compress further" (#61932).
Cap the prune message floor at the same bound as tail-cut, and under
pressure demote bulky protected-tail tool bodies (keeping a short recent
floor) so preflight can reclaim headroom without wiping the active ask.
Teknium
giggling-ginger