The names for the pieces are confusing, so it's easy to talk past each other. For instance, you're saying "Codex the agent", which isn't a thing now. It's currently GPT-5.5, and at one point it was GPT-5.3-Codex, so when I say "Codex", I meant the MacOS "harness". Similar for Claude Code vs Claude Opus/Sonnet.

Anyways, I don't know specifics well enough to argue with you on anything, but there is a cost for input tokens, and you see/pay it when you use the API directly or through OpenRouter. Maybe you looked at the leaked source for the Claude Code and can tell me definitively otherwise, but Anthropics and OpenAI's incentives for when to compact are not always aligned with the users depending on pricing plans.