Refact Agent Engine API
Local HTTP/LSP API exposed by the Rust `refact-lsp` engine that runs inside the user's IDE or as a standalone server. Implements the agent runtime: provider/model capabilities, chat command queueing, SSE event streams, code completion, tool registry and confirmation rules, AST indexing, RAG/vector search over the workspace, integrations configuration, knowledge graph operations, task board management, and workspace checkpoint/rollback. This is the contract the VS Code and JetBrains plugins and the GUI call over `http://127.0.0.1:/v1`.