Under the hood
- Added a code-mode protocol host codec along with remote session handling, connection drivers, readers, and cleanup logic.
- Introduced an executor plugin in the connectors crate and a JSONL event processor in exec.
- Expanded environment variable support with new CODEX_* entries for CA certificates, code mode host paths, exec server URLs, network profiles, and permission profiles.
- Added numerous serde structs, enums, events, and typed payloads to support delegate requests, host responses, wire runtime results, MCP server matching, thread management, and related flows.