333275162f
Harvested from PR #2639 by @gaord. Adds POST /v1/sessions for runtime clients to persist completed threads as managed saved sessions, with a 409 guard for queued or active turn/item state and focused session endpoint coverage. Also makes MCP HTTP tests install the rustls ring provider before constructing reqwest clients so filtered no-provider test runs are deterministic. Co-authored-by: gaord <9567937+gaord@users.noreply.github.com>