MCP Tasks Primitive (SEP-1686)

A Specification Enhancement Proposal (SEP-1686) for the Model Context Protocol that introduces a generic, cross-request **asynchronous state machine** — the "Tasks" primitive — augmenting any existing MCP request type. Under SEP-1686, a client dispatches a task-augmented request and immediately receives a `CreateTaskResult` containing a durable task ID; the actual execution runs server-side and the client later polls `tasks/get` or fetches with `tasks/result`.

Pre-SEP-1686 MCP was effectively synchronous — a tool call had to complete inside the transport timeout, blocking the agent's planning loop for the entire duration. Long-running operations (multi-hour ETL jobs, codebase migrations, large file conversions) routinely timed out. Developers worked around this with hand-rolled `start_job` / `check_status` / `get_results` triples, but the polling logic relied on prompt-engineering the model into a polling loop — hallucination-prone, expensive, inconsistent across servers. SEP-1686 standardizes the long-running primitive at the protocol level.