Honestly probably not a PR from me right now — I'm in the middle of shipping something else — but the design idea I keep returning to is splitting the trigger into two signals:

1. Runtime-computed "context pressure" — tokens-since-last-compaction, depth of tool-call nesting, response/call ratio in recent turns. The runtime computes this; the model never sees it.

2. Model-emitted "natural breakpoint" — a tool call the model fires when it perceives it's done with a thread (file closed, task complete, branch abandoned).

Compaction fires on the AND of both. Keeps the model from compacting mid-reasoning-chain, and keeps the runtime from waiting until 90% context for the model to notice on its own.