Forge does have tiered compaction, and it's configurable! Defaults are currently probably a bit on the high side for catching effective attention, but that might be a part of the code that interests you the most.

src/forge/context/ - specifically TieredCompact in strategies.py. That's the furthest I took it. The tool-call collapse in particular has been useful in agentic coding, but I haven't formalized/generalized it yet. I think within forge it'll be a callable tool that will rely on the model knowing when to trigger it (as you said - "I'm done with the task, can collapse"). That's the part I need to abstract out of my bespoke implementation.