Choose which old messages to drop to hit a token target without touching the cached prompt prefix

Overview

Given a conversation, the index of the last message inside the provider's cached prefix, and a token target, returns which messages to drop: whole tool call plus tool result pairs (so no result is left without its call) and messages the caller marked droppable, oldest first or largest first, never inside the cached prefix, never the most recent keepRecent messages, never pinned ones. Everything up to the cache breakpoint stays byte-identical because it is never selected; the

Health