ADR 0002: Native sync and async separation

Context

Notebooks and services need both modes without event-loop ownership failures.

Decision

Maintain native sync and async transports, services, resolvers, clients, limiters, and backoff.

Alternatives

Running async from sync, running sync in executors, and a mutable mode flag were considered.

Consequences

The two paths have matching capabilities but explicit lifecycles.

Rejected shortcuts

Loop runners, loop patching, and hidden thread adaptation are rejected.

Operational implications

Users select Client or AsyncClient; injected resources remain caller-owned.