[dbernheisel]

Summary

• Add Phantom.Tasks. A tool returns {:reply, %Phantom.Tasks{}, session} to answer tools/call with a task (lib/phantom/tasks.ex, Router.finalize_result/5).
• Phantom does not store tasks. The router implements get_task/2 to enable the extension. update_task/3, cancel_task/2, and authorize_task_subscriptions/2 are optional (lib/phantom/router.ex).
• Dispatch tasks/get, tasks/update, and tasks/cancel under MCP 2026-07-28. Return -32021 when the request does not declare the extension, -32602 for an unknown task, and -32601 when the router does not implement tasks.
• Require Mcp-Name to equal taskId on tasks/* (lib/phantom/plug.ex).
• Accept taskIds on subscriptions/listen. Phantom.Tracker.notify_task_updated/1 sends notifications/tasks. Each stream fetches the task with get_task/2 before it sends, and stops following a finished task.
• Add Phantom.Session.tasks_supported?/1, Phantom.Request.missing_task_capability/0, Phantom.Elicit.to_input_request/1, and Phantom.Test task helpers.
• Add Phantom.Session.progress_ref/1. It gives a JSON-safe reference to the current request. A job on any node sends progress with Phantom.Session.notify_progress/4. The request stream subscribes to a PubSub topic for the request before the handler runs.
• Run the 10 tasks scenarios of the conformance suite on the single and the distributed topology. They must pass.
• Add guides/tasks.md with examples for Ecto, Oban, and Oban Pro.
• Deferred: a limit on the length of taskIds, a capability check on task inputRequests, and removal of the duplicated fail-closed and notification blocks that the resource code also has.

Evidence

Run with MIX_ENV=test iex -S mix. The conformance router runs over Bandit. Req sends the requests over HTTP. The first task asks for input, gets it, and completes. The second task is cancelled while it works.

iex

iex> Phantom.Cache.register(Phantom.Conformance.MCP.Router)
iex> {:ok, _} = Bandit.start_link(plug: {Phantom.Test.ClusterPlug, phantom_opts: [router: Phantom.Conformance.MCP.Router, validate_origin: false]}, port: 4199)
iex> meta = %{"io.modelcontextprotocol/protocolVersion" => "2026-07-28", "io.modelcontextprotocol/clientCapabilities" => %{"elicitation" => %{}, "extensions" => %{"io.modelcontextprotocol/tasks" => %{}}}}
iex> mcp = fn method, params, name -> Req.post!("http://127.0.0.1:4199/", json: %{jsonrpc: "2.0", id: 1, method: method, params: Map.put(params, "_meta", meta)}, headers: [{"accept", "application/json, text/event-stream"}, {"mcp-protocol-version", "2026-07-28"}, {"mcp-method", method}, {"mcp-name", name}]).body |> String.split("\n") |> Enum.find_value(fn "data: " <> json -> JSON.decode!(json); _ -> nil end) |> then(&(&1["result"] || &1["error"])) |> Map.delete("_meta") end
iex> %{"taskId" => id} = mcp.("tools/call", %{"name" => "confirm_delete", "arguments" => %{"filename" => "report.csv"}}, "confirm_delete")
%{
  "createdAt" => "2026-10-04T23:04:52.691146Z",
  "lastUpdatedAt" => "2026-10-04T23:04:52.691146Z",
  "pollIntervalMs" => 200,
  "resultType" => "task",
  "status" => "input_required",
  "taskId" => "p4l1VSc4Z8r8RFWTwLmcsJsISFyKGfXJOGopJPFOyBo",
  "ttlMs" => 300000
}
iex> mcp.("tasks/get", %{"taskId" => id}, id)
%{
  "createdAt" => "2026-10-04T23:04:52.691146Z",
  "inputRequests" => %{
    "confirm" => %{
      "method" => "elicitation/create",
      "params" => %{
        "message" => "Delete report.csv?",
        "requestedSchema" => %{
          "properties" => %{"confirm" => %{"type" => "boolean"}},
          "required" => ["confirm"],
          "type" => "object"
        }
      }
    }
  },
  "lastUpdatedAt" => "2026-10-04T23:04:52.691146Z",
  "pollIntervalMs" => 200,
  "resultType" => "complete",
  "status" => "input_required",
  "taskId" => "p4l1VSc4Z8r8RFWTwLmcsJsISFyKGfXJOGopJPFOyBo",
  "ttlMs" => 300000
}
iex> mcp.("tasks/update", %{"taskId" => id, "inputResponses" => %{"confirm" => %{"action" => "accept", "content" => %{"confirm" => true}}}}, id)
%{"resultType" => "complete"}
iex> mcp.("tasks/get", %{"taskId" => id}, id)
%{
  "createdAt" => "2026-10-04T23:04:52.691146Z",
  "lastUpdatedAt" => "2026-10-04T23:04:52.696437Z",
  "pollIntervalMs" => 200,
  "result" => %{
    "content" => [%{"text" => "Deleted report.csv", "type" => "text"}]
  },
  "resultType" => "complete",
  "status" => "completed",
  "taskId" => "p4l1VSc4Z8r8RFWTwLmcsJsISFyKGfXJOGopJPFOyBo",
  "ttlMs" => 300000
}
iex> %{"taskId" => slow} = mcp.("tools/call", %{"name" => "slow_compute", "arguments" => %{"seconds" => 60, "label" => "demo"}}, "slow_compute")
%{
  "createdAt" => "2026-10-04T23:04:52.697175Z",
  "lastUpdatedAt" => "2026-10-04T23:04:52.697175Z",
  "pollIntervalMs" => 200,
  "resultType" => "task",
  "status" => "working",
  "taskId" => "3uYS-CwMwXR54a31TV8Hw7GTYO2QqJIOM77G6vNXcRA",
  "ttlMs" => 300000
}
iex> mcp.("tasks/cancel", %{"taskId" => slow}, slow)
%{"resultType" => "complete"}
iex> mcp.("tasks/get", %{"taskId" => slow}, slow)
%{
  "createdAt" => "2026-10-04T23:04:52.697175Z",
  "lastUpdatedAt" => "2026-10-04T23:04:52.697534Z",
  "pollIntervalMs" => 200,
  "resultType" => "complete",
  "status" => "cancelled",
  "statusMessage" => "Cancelled by the client",
  "taskId" => "3uYS-CwMwXR54a31TV8Hw7GTYO2QqJIOM77G6vNXcRA",
  "ttlMs" => 300000
}
iex> mcp.("tasks/get", %{"taskId" => "nope"}, "nope")
%{"code" => -32602, "message" => "Failed to retrieve task: Task not found"}

Conformance: mix test test/conformance/conformance_test.exs --include conformance passes 30 of 30, which includes the 10 tasks scenarios on both topologies.