feat(tasks): serve the MCP Tasks extension

.github/workflows/ci.yml

@@ -19,6 +19,8 @@ jobs:
             otp: "27"
           - elixir: "1.20"
             otp: "29"
+            # Formatter output differs between Elixir versions.
+            check_format: true
 
     steps:
       - uses: actions/checkout@v7
@@ -52,6 +54,7 @@ jobs:
         run: mix deps.unlock --check-unused
 
       - name: Check formatting
+        if: matrix.check_format
         run: mix format --check-formatted
 
       - name: Compile (warnings as errors)

CHANGELOG.md

@@ -1,5 +1,30 @@
 ## Unreleased
 
+- New: the Tasks extension (`io.modelcontextprotocol/tasks`) under MCP
+  2026-07-28. A tool returns `{:reply, %Phantom.Tasks{}, session}` to answer
+  with a task, and the router implements `c:Phantom.Router.get_task/2`, and
+  optionally `update_task/3`, `cancel_task/2`, and
+  `authorize_task_subscriptions/2`, for `tasks/get`, `tasks/update`, and
+  `tasks/cancel`. Phantom does not store tasks. See the Tasks guide for Ecto
+  and Oban examples.
+- New: `Phantom.Session.tasks_supported?/1`, and
+  `Phantom.Tracker.notify_task_updated/1`. Each `subscriptions/listen` stream
+  that follows the task fetches it with `get_task/2` and sends
+  `notifications/tasks`.
+- New: `Phantom.Test.get_task/3`, `update_task/4`, `cancel_task/3`,
+  `assert_task/2`, and a `:tasks` option for `call_tool/4`.
+- New: `Phantom.Session.progress_ref/1` returns a JSON-safe reference to the
+  current request. `Phantom.Session.notify_progress/4` accepts it, so a job
+  on any node can report progress to a waiting `tools/call` or `prompts/get`
+  through PubSub.
+- New: `Phantom.Elicit.to_input_request/1` renders one embedded
+  `elicitation/create` request to place under your own `inputRequests` key,
+  such as a task's input requests.
+- New: `Phantom.Request.missing_task_capability/0`, the error for a tool that
+  only runs as a task when the client did not declare the extension.
+- `Phantom.Request.missing_capability/1` accepts a `ClientCapabilities` map,
+  for capabilities whose names contain dots.
+
 Streamable HTTP transport fixes for the protocol versions before 2026-07-28:
 
 - New: `Phantom.Plug` option `validate_session: true` answers `404 Not Found`

README.md

@@ -717,6 +717,10 @@ Phantom will implement these MCP requests on your behalf:
   `input_required` result + encrypted `requestState`; both flows go through
   `Phantom.Session.elicit/3` and behave identically from the tool's point
   of view.
+- `tasks/get`, `tasks/update`, `tasks/cancel` - the Tasks extension under MCP
+  `2026-07-28`, when the router implements `c:Phantom.Router.get_task/2`. A tool
+  answers with a `Phantom.Tasks` and you store and run the task, such as with
+  Oban. See the [Tasks guide](guides/tasks.md).
 
 Phantom **does not yet support these methods**:
 
@@ -872,8 +876,10 @@ the JSON-RPC body into HTTP headers so load balancers, proxies, and WAFs
 can route on the operation without parsing the body:
 
 - `Mcp-Method` — mirrors `method`. Required on every POST.
-- `Mcp-Name` — mirrors `params.name` (for `tools/call`, `prompts/get`)
-  or `params.uri` (for `resources/read`).
+- `Mcp-Name` — mirrors `params.name` (for `tools/call`, `prompts/get`),
+  `params.uri` (for `resources/read`), or `params.taskId` (for `tasks/get`,
+  `tasks/update`, `tasks/cancel`). Route on it when tasks live in one node's
+  memory.
 
 Header names are case-insensitive; values are case-sensitive (so
 `Mcp-Method: TOOLS/CALL` does *not* match a body method of `tools/call`).