Previously every executor took `_state: AppState` (unused) and `check_auth`
discarded the matched downstream key id, so `usage_logs` was orphan code.
This change plumbs the key id from auth → handlers → executors → billing,
adds the OpenAI Responses API endpoint, and exposes shim aliases under
`/api/comfyui-agent/proxy/openai/*` so embedded ComfyUI's OpenAI nodes
flow through the same auth/conductor/billing pipeline.
- check_auth now returns Option<i64> (managed key id) instead of unit
- record_billing helper writes usage_logs after each successful upstream call
- extract_usage handles both chat-completions and responses usage shapes
- conductor wrappers record billing post-Success; stream variant scans
chunks in reverse for the final usage event
- POST /v1/responses (stream + non-stream) via ProxyConductor
- shim aliases mounted on the same Router so auth/failover/billing work for free
- ComfyUIProcess injects BOOSAPI_BUILTIN_KEY env + --comfy-api-base on spawn
- bootstrap built-in `comfyui-agent` downstream key at startup (idempotent)
- get_auth_header in vendored ComfyUI falls back to BOOSAPI_BUILTIN_KEY env
Co-Authored-By: Kiro <noreply@kiro.dev>
boos