Context estimate very incorrect when using with local strata server #96

When using Strata locally, I'm seeing agentty report 65.0k/65.5k while streaming a response, and then sometimes resetting down to the actual 33.0k/65.5k context size after the request completes. I'm often seeing the context size reported by agentty report being above 100% even though the strata web dashboard reports it at a much lower value. This makes the context usage estimate extremely unreliable as it rarely reports anything near what is in actual use.

Strata makes current prompt token usage available in the /metrics endpoint at .live.prompt_tokens, which can be used instead of guessing current context usage.