[Schema][Server][SEP-1686] Tasks

[chr-hertel]

Issue to track and address implementation of SEP-1686:

This SEP improves support for task-based workflows in the Model Context Protocol (MCP). It introduces both the task primitive and the associated task ID, which can be used to query the state and results of a task, up to a server-defined duration after the task has completed. This primitive is designed to augment other requests (such as tool calls) to enable call-now, fetch-later execution patterns across all requests for servers that support this primitive.

Spec Changes: https://github.com/modelcontextprotocol/modelcontextprotocol/pull/1732/files
Reference Implementation: modelcontextprotocol/typescript-sdk#1041

[LucaButBoring]

Relaying here from #general-sdk-dev:

There doesn't seem to be a central ticket for all SDK implementations of a particular change, so sharing this here for SEP-1686 -- the following revisions have been merged on top of the base specification PR for tasks:

• Clarify request lifetimes in task diagrams: PR
• Fix capability phrasing in spec: PR
• Remove an incorrectly-added field from notifications/cancelled: PR
• Adjust schema to better-communicate where tasks are valid: PR
• Rename/move annotations.taskHint to execution.taskSupport, tweak its enum values, and change a SHOULD to a MUST for the behavior when this is declared:
  • PR 1
  • PR 2
• GetTask polling clarification: PR
• SSE stream management clarification: PR

The actual functional changes should be limited to taskHint, but the rest should help clarify some details around polling.

To save the trouble of going through each of the above PRs one by one, you can also go to the file on the "Files changed" tab here, searching for docs/specification/draft/basic/utilities/tasks.mdx, and then using the "Display the rich diff" button, as shown:

[LucaButBoring]

One very last change (we're doing a hard cutoff on additional changes here): adding a lastUpdatedAt to the Task object: modelcontextprotocol/modelcontextprotocol#1875