Implements the schema portion of SEP-2663 for the MCP Spec 2026-07-28 release.

Tracked by umbrella #335. Depends on SEP-2133 extensions framework.

Spec summary

Reframes Tasks as a stateless, server-directed extension. Servers may respond to any tools/call (or any future task-augmented method) with a polymorphic result discriminated by resultType: "task" — a task handle — instead of a final result. Clients then poll via tasks/get, tasks/update, and tasks/cancel.

PHP SDK changes

• Add Task shape under src/Schema/: taskId, status enum (pending/running/input_required/completed/cancelled/failed), result, error, list of pending server-to-client requests.
• Add resultType: "task" discriminator on CallToolResult (and any other task-augmentable result types).
• Add TaskGetRequest/Result, TaskUpdateRequest/Result, TaskCancelRequest/Result under src/Schema/Request/ and src/Schema/Result/.
• Add task status enum under src/Schema/Enum/.

Notes

SEP-2663 supersedes SEP-1686. Issue #139 (SEP-1686 Tasks placeholder) is being closed in favor of this milestone.

Related

• Umbrella [2026-07-28] Extensions framework + Tasks + MCP Apps #335
• Blocked by SEP-2133 extension framework issue