Tasks SEP-1686: In-progress results

What's broken?

The spec doesn't cover a case it clearly should

Where in the spec or docs?

https://github.com/modelcontextprotocol/modelcontextprotocol/blob/8d07c35d3857412a351c595fe01b7bc70664ba06/seps/1686-tasks.md

What should happen?

(this is a feature request more than an issue, but I couldn't find a more appropriate place to put it)

The tasks SEP currently assumes that no information is available about a task until it completes, after which its results can be queried. For many sorts of tasks, this is not true. For example, for a background process, the agent may want to get the current STDOUT so it can check it's status.

While there is apparently a statusMessage (I didn't see it in the SEP, but it was mentioned in https://github.com/modelcontextprotocol/modelcontextprotocol/issues/1955), I do not think that serves this need. That provides a short status update, while this would get the entire results (often much larger), just only what is available currently.

What actually happens?

There is no way to check the output (not just status) of an in-progress task until it completes.

Anything else?

In my Gradle MCP, my "run a task in the background" tool provides a way to get the current results, including the tasks and tests ran. IME this is rather frequently used by agents for longer builds, especially if they suspect a task or test is hanging.

Start with seps/1686-tasks.md and the discussion in issue #1955, then compare the task behavior described here with the Gradle MCP example. Define how an in-progress task exposes currently available results, distinct from statusMessage, and document the behavior in the SEP. Done means the specification covers querying partial output before completion.