fix: make generated schema.json enforce spec constraints (#18)

The generated JSON Schema artifact previously failed to encode several
normative requirements, forcing non-TypeScript implementations to
maintain their own mirrors of core shapes and discriminators:

- InputRequest/InputResponse collapsed to anyOf:[{},{},{}] because the
  imported request/result types resolved to empty schemas, accepting
  any instance.
- The required resultType discriminators ('task' on CreateTaskResult,
  'complete' on Get/Update/CancelTaskResult) appeared nowhere in the
  artifact despite being normative MUSTs in the extension prose.
- Strip-mode object emission produced additionalProperties:false inside
  allOf intersections, making CreateTaskResult unsatisfiable: every
  spec-conformant instance (with resultType or _meta) was rejected.

The canonical specification is now the sole source of truth for all
core-spec shapes — no SDK package is consulted at any layer.
scripts/fetch-spec-schema.ts vendors spec.schema.json and spec.types.ts
from the same recorded spec commit with provenance headers:

- schema.ts imports every core type (JSON-RPC envelopes, Result,
  NotificationParams, the MRTR InputRequests/InputResponses, and the
  JSON-RPC Error object) from the vendored spec.types.ts, deleting the
  local mirrors that had already drifted from upstream.
- generate-schemas.ts emits $ref for all spec-owned types — including
  the JSON-RPC envelopes intersected by the extension's own types — and
  splices their transitive $ref closure verbatim from the vendored
  canonical schema.json. Core-spec corrections flow in via an explicit,
  reviewable refresh (npm run fetch:spec-schema) instead of silently
  diverging. The @modelcontextprotocol/sdk devDependency is removed.
- Runtime Zod stand-ins for imported types are permissive locals whose
  shapes never reach the artifact; generation fails on any unmapped
  placeholder, and on any definition that cannot be converted.
- JSON Schema emission uses io:'input' so TypeScript's open interface
  semantics are preserved and intersections remain satisfiable.
- resultType discriminators are encoded structurally in schema.ts.
- FailedTask.error now requires the canonical JSON-RPC Error shape;
  ttlMs and pollIntervalMs are integers per the prose.
- createdAt/lastUpdatedAt deliberately remain unconstrained strings:
  the prose requires ISO 8601 generally, and JSON Schema's date-time
  format/pattern machinery can only express RFC 3339, which would
  reject valid basic-form timestamps.

Validated with a Draft 2020-12 jsonschema matrix covering union
rejection/acceptance, discriminator enforcement, JSON-RPC envelope
enforcement, error-shape and integer constraints, byte-fidelity of all
56 spliced canonical definitions, complete $ref resolution, and
check-mode idempotency.

schema/draft/schema.ts

@@ -12,17 +12,14 @@
  */
 
 import type {
-  CreateMessageRequest,
-  CreateMessageResult,
-  ElicitRequest,
-  ElicitResult,
+  Error as JSONRPCErrorObject,
+  InputRequests,
+  InputResponses,
   JSONRPCNotification,
   JSONRPCRequest,
-  ListRootsRequest,
-  ListRootsResult,
   NotificationParams,
   Result,
-} from "@modelcontextprotocol/sdk/types.js";
+} from "./spec.types.js";
 
 /* Tasks */
 
@@ -79,6 +76,7 @@ export interface Task {
    * Time-to-live duration from creation in integer milliseconds, null for unlimited.
    * The server may discard the task after the TTL elapses. This value MAY change
    * over the lifetime of a task.
+   * @format int
    * @nullable
    */
   ttlMs: number | null;
@@ -87,6 +85,7 @@ export interface Task {
    * Suggested polling interval in integer milliseconds. Clients SHOULD honor
    * this value to avoid overwhelming the server. This value MAY change over
    * the lifetime of a task.
+   * @format int
    */
   pollIntervalMs?: number;
 }
@@ -103,51 +102,6 @@ export interface WorkingTask extends Task {
   status: "working";
 }
 
-/**
- * A single input request from the server to the client during task execution.
- *
- * @category `tasks`
- */
-// TODO: Import from SDK once updated for MRTR
-export type InputRequest =
-  | CreateMessageRequest
-  | ListRootsRequest
-  | ElicitRequest;
-
-/**
- * A single input response from the client to the server during task execution.
- *
- * @category `tasks`
- */
-// TODO: Import from SDK once updated for MRTR
-export type InputResponse =
-  | CreateMessageResult
-  | ListRootsResult
-  | ElicitResult;
-
-/**
- * Outstanding server-to-client requests that need to be fulfilled during task execution.
- * Keys are arbitrary identifiers for matching requests to responses. Each key MUST be
- * unique over the lifetime of a single task.
- *
- * @category `tasks`
- */
-// TODO: Import from SDK once updated for MRTR
-export interface InputRequests {
-  [key: string]: InputRequest;
-}
-
-/**
- * Client responses to outstanding input requests. Each key MUST correspond to a
- * currently-outstanding inputRequest key.
- *
- * @category `tasks`
- */
-// TODO: Import from SDK once updated for MRTR
-export interface InputResponses {
-  [key: string]: InputResponse;
-}
-
 /**
  * A task that is waiting for input from the client.
  * Used by tasks/get and notifications/tasks.
@@ -193,7 +147,7 @@ export interface FailedTask extends Task {
   /**
    * The JSON-RPC error that caused the task to fail.
    */
-  error: { [key: string]: unknown };
+  error: JSONRPCErrorObject;
 }
 
 /**
@@ -230,7 +184,13 @@ export type DetailedTask =
  *
  * @category `tasks`
  */
-export type CreateTaskResult = Result & Task;
+export type CreateTaskResult = Result &
+  Task & {
+    /**
+     * Discriminator distinguishing a task handle from a standard result.
+     */
+    resultType: "task";
+  };
 
 /* Task Operations */
 
@@ -239,7 +199,7 @@ export type CreateTaskResult = Result & Task;
  *
  * @category `tasks/get`
  */
-export interface GetTaskRequest extends JSONRPCRequest {
+export type GetTaskRequest = JSONRPCRequest & {
   method: "tasks/get";
   params: {
     /**
@@ -247,7 +207,7 @@ export interface GetTaskRequest extends JSONRPCRequest {
      */
     taskId: string;
   };
-}
+};
 
 /**
  * The response to a tasks/get request. Carries the appropriate DetailedTask
@@ -256,14 +216,20 @@ export interface GetTaskRequest extends JSONRPCRequest {
  *
  * @category `tasks/get`
  */
-export type GetTaskResult = Result & DetailedTask;
+export type GetTaskResult = Result &
+  DetailedTask & {
+    /**
+     * Discriminator marking this as the standard result shape for tasks/get.
+     */
+    resultType: "complete";
+  };
 
 /**
  * A request to provide input responses to a task in the input_required state.
  *
  * @category `tasks/update`
  */
-export interface UpdateTaskRequest extends JSONRPCRequest {
+export type UpdateTaskRequest = JSONRPCRequest & {
   method: "tasks/update";
   params: {
     /**
@@ -277,7 +243,7 @@ export interface UpdateTaskRequest extends JSONRPCRequest {
      */
     inputResponses: InputResponses;
   };
-}
+};
 
 /**
  * The response to a tasks/update request. An empty acknowledgement.
@@ -285,14 +251,19 @@ export interface UpdateTaskRequest extends JSONRPCRequest {
  *
  * @category `tasks/update`
  */
-export type UpdateTaskResult = Result;
+export type UpdateTaskResult = Result & {
+  /**
+   * Discriminator marking this as the standard result shape for tasks/update.
+   */
+  resultType: "complete";
+};
 
 /**
  * A request to cancel a task.
  *
  * @category `tasks/cancel`
  */
-export interface CancelTaskRequest extends JSONRPCRequest {
+export type CancelTaskRequest = JSONRPCRequest & {
   method: "tasks/cancel";
   params: {
     /**
@@ -300,7 +271,7 @@ export interface CancelTaskRequest extends JSONRPCRequest {
      */
     taskId: string;
   };
-}
+};
 
 /**
  * The response to a tasks/cancel request. An empty acknowledgement.
@@ -309,7 +280,12 @@ export interface CancelTaskRequest extends JSONRPCRequest {
  *
  * @category `tasks/cancel`
  */
-export type CancelTaskResult = Result;
+export type CancelTaskResult = Result & {
+  /**
+   * Discriminator marking this as the standard result shape for tasks/cancel.
+   */
+  resultType: "complete";
+};
 
 /* Task Notifications */
 
@@ -329,10 +305,10 @@ export type TaskStatusNotificationParams = NotificationParams &
  *
  * @category `notifications/tasks`
  */
-export interface TaskStatusNotification extends JSONRPCNotification {
+export type TaskStatusNotification = JSONRPCNotification & {
   method: "notifications/tasks";
   params: TaskStatusNotificationParams;
-}
+};
 
 /* Subscription Additions */