Implements the long-running execution path for SEP-2663 for the MCP Spec 2026-07-28 release.

Tracked by umbrella #335. Largest design decision in this milestone.

Spec summary

Tools can opt into task-eligible execution. The runtime returns a task handle early; the tool body continues running asynchronously and writes progress/results to the task store. Subsequent tasks/get/tasks/update calls read from the store.

PHP SDK changes

• Extend #[McpTool] (or add a sibling marker) to signal task-eligibility.
• src/Capability/Registry/Handler/ReferenceHandler.php: today the Fiber either returns a result or suspends for sampling/elicitation. Add a path where the handler returns early with a task handle and continues running.
• Open design question: how does a PHP server keep a task progressing between HTTP requests? Options to evaluate:
  • Push the tool body onto a queue worker (Symfony Messenger / queue interface).
  • Spawn a detached process / use fastcgi_finish_request.
  • Require user-supplied background executor (lightweight strategy interface).
• Extend tools/call handler in src/Server/Handler/Request/ to honor the negotiated tasks extension and emit a task handle when the runtime defers.

Related

• Umbrella [2026-07-28] Extensions framework + Tasks + MCP Apps #335
• Depends on: SEP-2133 framework, SEP-2663 schema, SEP-2663 store