feat(ext-tasks): server dispatch wiring — SEP-2663 runtime on the 2026 lane

Opt-in ext-tasks feature on turul-mcp-server (off by default per
SEP-2133); dispatcher design recorded in ADR-028 (2026-06-12 entry):

- .with_ext_tasks(store): advertises io.modelcontextprotocol/tasks in
  discover capabilities.extensions, registers tasks/get|update|cancel
- .ext_task_tool(_required): task election per the upstream lifecycle —
  declared per-request extension → durable CreateTaskResult (UUIDv4
  bearer-grade id, store written BEFORE the response) + spawned worker;
  undeclared → sync fallback (progressive enhancement) or -32003 with
  data.requiredCapabilities.extensions for required tools
- MRTR bridge: a task tool returning McpError::InputRequired parks in
  input_required; tasks/update validates keys against outstanding
  requests (partial delivery keeps it parked) and resumes the worker
  with responses injected through the same session-extension keys as
  the sync retry leg — tool code identical under both execution models
- tasks/cancel cooperative (aborts worker, drops waiters, acks
  terminal); notifications/tasks rides subscriptions/listen with
  taskIds honored iff the extension is advertised (capability-map
  keyed — no transport dependency on the ext crate), echoed in the ack
- turul-mcp-ext-tasks: TaskStore trait + TaskState + InMemoryTaskStore
  (state machine enforced; no tokio in the public API)

9 wire e2e tests (ext_tasks_2026.rs; gates + CI steps added): discover
advertisement, create→poll→completed, sync fallback, -32003 shape,
input_required⇄update round trip incl. requestState replay, cancel,
unknown-task -32602, UUIDv4 ids, taskIds-filtered listen delivery.
Revert-and-fail recorded: neutralizing the capability check fails
declared_call_returns_task_and_polls_to_completion with a sync result.
Driver-doc Major-6 (SEP-2663) promoted to ✅ (G1 closed).

Full ci-gates.sh all green.

Author: hortovanyi

.github/workflows/ci.yml

@@ -72,6 +72,10 @@ jobs:
         run: cargo build -p streamable-http-client
       - name: Client-using examples (not in default-members)
         run: cargo build -p mrtr-elicitation-server --bins -p bilingual-fleet-client
+      - name: Tasks extension (SEP-2663, opt-in feature)
+        run: cargo test -p turul-mcp-server --no-default-features --features http,sse,ext-tasks --test ext_tasks_2026
+      - name: Extension crates standalone
+        run: cargo test -p turul-mcp-ext-tasks -p turul-mcp-ext-apps
 
   opt-in-2025:
     name: Opt-in lane (2025-11-25)

CHANGELOG.md

@@ -20,6 +20,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Added
 
+- **Tasks-extension server runtime (2026-06-12, SEP-2663 — closes driver gap G1).** New opt-in `ext-tasks` feature on `turul-mcp-server` (off by default per SEP-2133): `.with_ext_tasks(store)` advertises `io.modelcontextprotocol/tasks` in `server/discover`'s `capabilities.extensions` and registers `tasks/get`/`tasks/update`/`tasks/cancel`; `.ext_task_tool(tool)` / `.ext_task_tool_required(tool)` mark tools for task election — a request whose per-request `_meta` `clientCapabilities.extensions` declares the extension gets a durable `CreateTaskResult` (UUIDv4 bearer-grade id, store written BEFORE the response) with a spawned worker; undeclared requests run synchronously (progressive enhancement) or, for `_required` tools, get `-32003` with the upstream `data.requiredCapabilities.extensions` shape. **MRTR bridge**: a task tool returning `McpError::InputRequired` parks its task in `input_required`; `tasks/update` validates response keys against outstanding requests (partial delivery keeps it parked) and resumes the worker with the responses injected through the same session-extension keys as the sync retry leg — tool code is identical under both execution models. `tasks/cancel` is cooperative (aborts the worker, drops input waiters, acks terminal tasks). `notifications/tasks` rides `subscriptions/listen`: the transport honors a `taskIds` filter iff the extension is advertised (keyed off the capability map — no transport dependency on the ext crate), echoes it in the ack, and delivers per-taskId. `turul-mcp-ext-tasks` gains the `TaskStore` trait + `TaskState` + `InMemoryTaskStore` (no tokio in the public API). 9 wire e2e tests (`ext_tasks_2026.rs`, wired into gates + CI); revert-and-fail recorded. Dispatcher design recorded in ADR-028 (2026-06-12 entry).
 - **`turul-mcp-ext-apps` 0.1.0 scaffold (2026-06-12, SEP-1865).** Spec-neutral extension crate binding the MCP-side Apps surface: extension identifier `io.modelcontextprotocol/ui` (the ADR-028 table's `/apps` guess corrected against upstream), client capability (`UiClientCapabilities.mimeTypes` + the `text/html;profile=mcp-app` HTML-views gate), tool `_meta.ui` (`UiToolMeta`: `resourceUri`, `visibility` model/app), and UI-resource `_meta.ui` (`UiResourceMeta`: CSP domain lists, sandbox permissions, dedicated origin, `prefersBorder`). The host↔view iframe protocol is deliberately not bound (app/host SDK scope). Vendored spec pinned at `modelcontextprotocol/ext-apps@ca1d2989`; 5 wire-shape compliance tests.
 - **Versioning/cancellation/elicitation P2 trio (2026-06-12).** (1) **VER-4**: the headerless-`initialize` rejection (400 + `-32001`) now carries `error.data.supported` naming this build's protocol versions — a true legacy client's only diagnostic; wire test `headerless_initialize_rejection_names_supported_versions`, red-phase recorded. (2) **PAT/G10**: dedicated `CancelledNotificationHandler` extracts `requestId` + `reason` from inbound `notifications/cancelled` into a structured log line ("Both parties SHOULD log cancellation reasons"); accepted-and-ignored semantics unchanged. (3) **CF/GAP-CF-8**: new `turul_mcp_builders::validate_elicit_content(schema, content)` validates elicited form content against the requesting schema (required/unknown keys, primitive types, string-length/numeric bounds, integer-ness, enum membership across the 2026 enum-union shapes; format assertions annotation-only by design) — central enforcement is impossible on the stateless lane (leg-1 schema not retained), so tools call it on the MRTR retry; wired into `mrtr-elicitation-server` and live-verified. Plus **BP-5** (COMPLIANCE.md §"Supported JSON Schema dialects" — the documentation the SHOULD asks for) and **UTIL/COMP-3** (relevance/fuzzy/rate-limit completion SHOULDs dispositioned: provider semantics + middleware rate limiting). Driver summary now 305 ✅ / 68 🟡 / 5 ❌ / 12 🧪 / 100 ➖ — the 5 remaining ❌ all carry recorded dispositions.
 - **`turul-mcp-ext-tasks` 0.1.0 scaffold (2026-06-12, SEP-2663).** New spec-neutral extension crate per ADR-028 (2026-06-07 amendment): the `v2026_07_28` module carries the redesigned Tasks-extension surface — status-tagged `DetailedTask` (working/input_required/completed/failed/cancelled with variant fields inlined), `CreateTaskResult` (`resultType: "task"`, flat `Result & Task`), `tasks/get`/`tasks/update`/`tasks/cancel` bindings, `notifications/tasks`, `taskIds` subscription-filter fields, and capability negotiation helpers including SEP-2133 identifier validation. Upstream schema vendored from `modelcontextprotocol/ext-tasks@8966bea9` with a provenance README; 13 wire-shape compliance tests (explicit-null `ttlMs`, snake_case status strings, flat task discriminator). `protocol-2026-07-28` is the default feature; `--no-default-features` compiles empty. Server dispatch wiring and the 2025-11-25 reconciliation module are tracked as separate slices (ADR-028 revision log 2026-06-12). Partially closes driver gap **G1** (SEP-2663 row stays 🟡 until dispatch lands).

Cargo.toml

@@ -223,6 +223,7 @@ turul-http-mcp-server = { version = "0.4.0", path = "crates/turul-http-mcp-serve
 turul-mcp-server = { version = "0.4.0", path = "crates/turul-mcp-server" }
 turul-mcp-derive = { version = "0.4.0", path = "crates/turul-mcp-derive" }
 turul-mcp-client = { version = "0.4.0", path = "crates/turul-mcp-client" }
+turul-mcp-ext-tasks = { version = "0.1.0", path = "crates/turul-mcp-ext-tasks" }
 turul-mcp-builders = { version = "0.4.0", path = "crates/turul-mcp-builders" }
 turul-mcp-aws-lambda = { version = "0.4.0", path = "crates/turul-mcp-aws-lambda" }
 turul-mcp-oauth = { version = "0.4.0", path = "crates/turul-mcp-oauth" }

crates/turul-http-mcp-server/src/streamable_http.rs

@@ -1993,6 +1993,28 @@ impl StreamableHttpHandler {
                 .filter(|uris| !uris.is_empty() && caps.resources.is_some()),
         };
 
+        // Tasks-extension filter addition (SEP-2663 `taskIds`): rides the same
+        // `notifications` object but is not a core-schema field, so it is read
+        // from the raw params; honored only when the server advertises
+        // `io.modelcontextprotocol/tasks` in `capabilities.extensions`.
+        let tasks_extension_advertised = caps
+            .extensions
+            .as_ref()
+            .is_some_and(|m| m.contains_key("io.modelcontextprotocol/tasks"));
+        let honored_task_ids: Option<Vec<String>> = request
+            .params
+            .as_ref()
+            .and_then(|p| serde_json::to_value(p).ok())
+            .as_ref()
+            .and_then(|v| v.pointer("/notifications/taskIds"))
+            .and_then(|v| v.as_array())
+            .map(|ids| {
+                ids.iter()
+                    .filter_map(|i| i.as_str().map(String::from))
+                    .collect::<Vec<_>>()
+            })
+            .filter(|ids| !ids.is_empty() && tasks_extension_advertised);
+
         // Gate delivery at the broadcast layer: the subscription registry entry is
         // created even when empty, so an empty filter delivers nothing (the
         // registry's no-entry default is allow-all).
@@ -2009,6 +2031,9 @@ impl StreamableHttpHandler {
         if honored.resource_subscriptions.is_some() {
             allowed_types.push("notifications/resources/updated".to_string());
         }
+        if honored_task_ids.is_some() {
+            allowed_types.push("notifications/tasks".to_string());
+        }
         self.stream_manager
             .subscribe_to_notifications(&session_id, allowed_types)
             .await;
@@ -2033,10 +2058,11 @@ impl StreamableHttpHandler {
 
         // Acknowledgement — wire-complete JSON-RPC notification, first frame.
         let mut ack_params = std::collections::HashMap::new();
-        ack_params.insert(
-            "notifications".to_string(),
-            serde_json::to_value(&honored).unwrap_or_default(),
-        );
+        let mut honored_value = serde_json::to_value(&honored).unwrap_or_default();
+        if let (Some(obj), Some(ids)) = (honored_value.as_object_mut(), honored_task_ids.as_ref()) {
+            obj.insert("taskIds".to_string(), serde_json::json!(ids));
+        }
+        ack_params.insert("notifications".to_string(), honored_value);
         ack_params.insert(
             "_meta".to_string(),
             serde_json::json!({ META_KEY_SUBSCRIPTION_ID: subscription_id }),
@@ -2054,6 +2080,7 @@ impl StreamableHttpHandler {
         // drops the rest — this is the per-URI filter plus defense in depth) and
         // stamp the subscription id into every delivered notification.
         let filter = honored;
+        let filter_task_ids = honored_task_ids;
         let sub_id = subscription_id;
         let live = ReceiverStream::new(rx).filter_map(move |ev| {
             let mut data = ev.data;
@@ -2077,6 +2104,17 @@ impl StreamableHttpHandler {
                         _ => false,
                     }
                 }
+                // Tasks extension (SEP-2663): per-taskId delivery.
+                "notifications/tasks" => {
+                    let task_id = data
+                        .get("params")
+                        .and_then(|p| p.get("taskId"))
+                        .and_then(|t| t.as_str());
+                    match (task_id, &filter_task_ids) {
+                        (Some(id), Some(ids)) => ids.iter().any(|x| x == id),
+                        _ => false,
+                    }
+                }
                 _ => false,
             };
             if !allowed {

crates/turul-mcp-ext-tasks/Cargo.toml

@@ -23,3 +23,6 @@ protocol-2026-07-28 = ["dep:turul-mcp-protocol-2026-07-28"]
 turul-mcp-protocol-2026-07-28 = { version = "0.4.0", path = "../turul-mcp-protocol-2026-07-28", optional = true }
 serde.workspace = true
 serde_json.workspace = true
+async-trait.workspace = true
+thiserror.workspace = true
+chrono.workspace = true

crates/turul-mcp-ext-tasks/src/lib.rs

@@ -20,7 +20,8 @@
 //!   `subscriptions/listen` with `taskIds` filter fields
 //!
 //! Adding this crate as a dependency is the opt-in — extensions are disabled
-//! by default. Schema provenance: `schema/README.md` (vendored from
+//! by default. Server-side dispatch lives in `turul-mcp-server` behind its
+//! `ext-tasks` feature (`.with_ext_tasks(store)` + `.ext_task_tool(...)`). Schema provenance: `schema/README.md` (vendored from
 //! `modelcontextprotocol/ext-tasks` at a pinned commit).
 //!
 //! See the SEP: <https://modelcontextprotocol.io/seps/2663-tasks-extension>.
@@ -31,9 +32,10 @@ pub mod v2026_07_28;
 #[cfg(feature = "protocol-2026-07-28")]
 pub use v2026_07_28::{
     CancelTaskParams, CreateTaskResult, DetailedTask, EXTENSION_IDENTIFIER, GetTaskParams,
-    GetTaskResult, InvalidExtensionIdentifier, METHOD_NOTIFICATIONS_TASKS, METHOD_TASKS_CANCEL,
-    METHOD_TASKS_GET, METHOD_TASKS_UPDATE, Nullable, RESULT_TYPE_TASK, Task, TaskAckResult,
-    TaskFields, TaskStatus, TaskStatusNotificationParams,
+    GetTaskResult, InMemoryTaskStore, InputDelivery, InvalidExtensionIdentifier,
+    METHOD_NOTIFICATIONS_TASKS, METHOD_TASKS_CANCEL, METHOD_TASKS_GET, METHOD_TASKS_UPDATE,
+    Nullable, RESULT_TYPE_TASK, Task, TaskAckResult, TaskFields, TaskState, TaskStatus,
+    TaskStatusNotificationParams, TaskStore, TaskStoreError,
     TaskSubscriptionAcknowledgedNotifications, TaskSubscriptionNotifications, UpdateTaskParams,
     capability, declared_by_client, declared_by_server, validate_identifier,
 };

crates/turul-mcp-ext-tasks/src/v2026_07_28/mod.rs

@@ -2,6 +2,7 @@
 
 pub mod capability;
 pub mod lifecycle;
+pub mod store;
 pub mod types;
 
 #[cfg(test)]
@@ -17,6 +18,7 @@ pub use lifecycle::{
     TaskStatusNotificationParams, TaskSubscriptionAcknowledgedNotifications,
     TaskSubscriptionNotifications, UpdateTaskParams,
 };
+pub use store::{InMemoryTaskStore, InputDelivery, TaskState, TaskStore, TaskStoreError};
 pub use types::{
     CreateTaskResult, DetailedTask, Nullable, RESULT_TYPE_TASK, Task, TaskFields, TaskStatus,
 };