API request telemetry gains time-to-first-content, per-attempt request IDs, and richer retry data

What

• The end-of-request telemetry (the api_request event and related completion logging) now tracks a firstContentMs value — time to first content — separately from time-to-first-token, and includes a ttft_ms field when that value is available.
• The main API-call success event, tengu_api_success, now also records firstContentMs, a client-generated request ID (clientRequestId), and the UUID of the originating user message (user_message_uuid).
• The API call dispatcher now generates a new clientRequestId for each attempt (sent as an extra header) and tracks an attempt counter, reporting request lifecycle telemetry — success/failure, status code, error class, attempt number, clientRequestId, requestId — plus a durationMs field on tengu_api_success that excludes time spent on retries.

Why These fields give much finer-grained visibility into API call performance and retry behavior, making it possible to distinguish slow model responses from network/retry overhead and to trace individual attempts by their request ID.