An optional OTLP endpoint #992

Parent

#700

What to build

A User config setting names an optional OTLP/HTTP endpoint. When one is set, each span is also sent there as it ends, so that a local viewer can receive it live.

• Sending is best effort. A failed or slow send never fails a session, and never delays it beyond a short bound.
• A Security run's sessions are never sent (ADR 0015).
• The setting is blank by default, and the User config's documented defaults and Setup describe it.

Acceptance criteria

• With a local test receiver, spans arrive as they end.
• With the receiver down, sessions finish as normal.
• A Security run's spans are never sent.
• The setting is blank by default and documented with the other User config defaults.