The gateway /usage handler only looked in _running_agents for the agent
object, which is only populated while the agent is actively processing a
message. Between turns (when users actually type /usage), the dict is
empty and the handler fell through to a rough message-count estimate.
The agent object actually lives in _agent_cache between turns (kept for
prompt caching). This fix checks both dicts, with _running_agents taking
priority (mid-turn) and _agent_cache as the between-turns fallback.
Also brings the gateway output to parity with the CLI /usage:
- Model name
- Detailed token breakdown (input, output, cache read, cache write)
- Cost estimation (estimated amount or 'included' for subscriptions)
- Cache token lines hidden when zero (cleaner output)
This fixes Nous Portal rate limit headers not showing up for gateway
users — the data was being captured correctly but the handler could
never see it.
