SDK v2 migration (behavior-neutral, versionNegotiation: 'legacy') (#1624)

Migrate all three clients + core + test-servers from
@modelcontextprotocol/sdk@1.29 to SDK v2 (2.0.0-beta.4), keeping behavior
identical against legacy (2025-11-25) servers. Foundation for the SDK V2 +
New Spec stack.

Packages
- Split @modelcontextprotocol/sdk -> @modelcontextprotocol/client (Client,
  transports, OAuth, error taxonomy, protocol types) + core (Zod schemas);
  stdio -> client/stdio, Ajv -> client/validators/ajv. Test-servers ->
  @modelcontextprotocol/server (+ server-legacy/sse). Deterministic import
  rewrite (schemas -> core, everything else -> client); the codemod misroutes
  client code to /server so it was not used for path routing.
- new Client(..., { versionNegotiation: { mode: 'legacy' } }) — nothing
  2026-era goes on the wire.

Runtime (core/mcp/inspectorClient.ts)
- Error taxonomy: McpError -> ProtocolError, ErrorCode -> ProtocolErrorCode;
  RequestTimeout -> SdkError/SdkErrorCode.
- Handlers take method strings; task methods (tasks/*, notifications/tasks/*)
  use the 3-arg custom form (excluded from v2's spec-method set).
- Legacy tasks kept working (per project requirement): requestor tasks re-
  implemented over raw client.request + explicit deprecated schemas;
  experimental.tasks.callToolStream replaced by a local pollTaskToolCall
  async generator (with _progressHandlers revival so task-execution progress
  still reaches the caller). Receiver (server-initiated) tasks: the v2 Client
  validates a sampling/elicit handler result and rejects the legacy { task }
  response with -32602 — installReceiverTaskResponseBypass swaps the wrapped
  entry in the private _requestHandlers map for the task-augmented branch so
  { task } reaches the wire (fixes server-initiated sampling-via-task).
- Pagination: list verbs use raw client.request({method}, List*ResultSchema)
  for single-page behavior (v2's client.listX() auto-aggregate all pages).

Web / auth / apps
- Rename local JsonSchemaType -> InspectorFormSchema + add toFormSchema()
  structural narrowing at the SDK-schema -> form boundary.
- ext-apps still peers on SDK v1: one compat boundary with documented casts
  (remove when ext-apps#702 lands a v2 peer).
- OAuth provider saveClientInformation reconciled with v2's
  OAuthClientInformationContext; InvalidClientMetadataError re-homed as a
  local class (server-legacy/auth is not browser-safe).
- vitest.shared.mts dedupes @modelcontextprotocol/client+core to one copy so
  vi.mock intercepts the SUT's import.

Accepted v2 behavior changes (per #1624 / spec §9.2): unknown-tool call
rejects with -32602; cancellation is stream-abort (no guaranteed
notifications/cancelled frame); output-schema strictness restored via the
Inspector's own Ajv check on the default path.

npm run ci green: validate (web 3087 / cli 212 / tui 274 / launcher 5),
coverage (>=90 per-file, all clients), smoke (launcher/cli/web), storybook
(410).

Closes #1624

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

clients/web/src/components/screens/AppsScreen/AppsScreen.stories.tsx

@@ -1,7 +1,7 @@
 import { useCallback, useRef, useState } from "react";
 import { Stack, Text } from "@mantine/core";
 import type { Meta, StoryObj } from "@storybook/react-vite";
-import type { CallToolResult, Tool } from "@modelcontextprotocol/sdk/types.js";
+import type { CallToolResult, Tool } from "@modelcontextprotocol/client";
 import type { AppBridge } from "@modelcontextprotocol/ext-apps/app-bridge";
 import { expect, fn, userEvent, waitFor, within } from "storybook/test";
 import {

clients/web/src/components/screens/AppsScreen/AppsScreen.test.tsx

@@ -3,7 +3,7 @@ import { act } from "@testing-library/react";
 import { describe, it, expect, vi } from "vitest";
 import userEvent from "@testing-library/user-event";
 import type { McpUiDisplayMode } from "@modelcontextprotocol/ext-apps/app-bridge";
-import type { ContentBlock, Tool } from "@modelcontextprotocol/sdk/types.js";
+import type { ContentBlock, Tool } from "@modelcontextprotocol/client";
 import type { AppBridge } from "@modelcontextprotocol/ext-apps/app-bridge";
 import {
   renderWithMantine,

clients/web/src/components/screens/AppsScreen/AppsScreen.tsx

@@ -25,7 +25,7 @@ import type {
   ContentBlock,
   LoggingMessageNotification,
   Tool,
-} from "@modelcontextprotocol/sdk/types.js";
+} from "@modelcontextprotocol/client";
 import type {
   AppBridgeEventMap,
   McpUiDisplayMode,
@@ -42,7 +42,7 @@ import { AppControls } from "../../groups/AppControls/AppControls";
 import { ContentViewer } from "../../elements/ContentViewer/ContentViewer";
 import { LogLevelBadge } from "../../elements/LogLevelBadge/LogLevelBadge";
 import { hasInputFields, resolveDisplayLabel } from "../../../utils/toolUtils";
-import { collectSchemaDefaults } from "../../../utils/jsonUtils";
+import { collectSchemaDefaults, toFormSchema } from "../../../utils/jsonUtils";
 
 export interface AppsScreenProps {
   tools: Tool[];
@@ -475,7 +475,7 @@ export function AppsScreen({
     onUiChange({
       ...ui,
       selectedAppName: name,
-      formValues: collectSchemaDefaults(next.inputSchema),
+      formValues: collectSchemaDefaults(toFormSchema(next.inputSchema) ?? {}),
     });
     setMaximized(false);
     resetAppChannels();

clients/web/src/components/screens/LoggingScreen/LoggingScreen.fixtures.ts

@@ -1,4 +1,4 @@
-import type { LoggingLevel } from "@modelcontextprotocol/sdk/types.js";
+import type { LoggingLevel } from "@modelcontextprotocol/client";
 import type { LogEntryData } from "../../elements/LogEntry/LogEntry";
 
 const logMessages: {

clients/web/src/components/screens/LoggingScreen/LoggingScreen.tsx

@@ -1,5 +1,5 @@
 import { Card, Flex, Stack } from "@mantine/core";
-import type { LoggingLevel } from "@modelcontextprotocol/sdk/types.js";
+import type { LoggingLevel } from "@modelcontextprotocol/client";
 import { LogControls } from "../../groups/LogControls/LogControls";
 import { LogStreamPanel } from "../../groups/LogStreamPanel/LogStreamPanel";
 import type { LogEntryData } from "../../elements/LogEntry/LogEntry";

clients/web/src/components/screens/LoggingScreen/logLevels.ts

@@ -1,4 +1,4 @@
-import type { LoggingLevel } from "@modelcontextprotocol/sdk/types.js";
+import type { LoggingLevel } from "@modelcontextprotocol/client";
 
 // Default visible-level filter: every level on. Shared by LoggingScreen (its
 // fallback when the parent hasn't set `visibleLevels`) and App, which seeds and

clients/web/src/components/screens/PromptsScreen/PromptsScreen.stories.tsx

@@ -1,7 +1,7 @@
 import { useState } from "react";
 import type { ComponentProps } from "react";
 import type { Meta, StoryObj } from "@storybook/react-vite";
-import type { Prompt } from "@modelcontextprotocol/sdk/types.js";
+import type { Prompt } from "@modelcontextprotocol/client";
 import { fn, userEvent, within } from "storybook/test";
 import { PromptsScreen } from "./PromptsScreen";
 import type { GetPromptState, PromptsUiState } from "./PromptsScreen";

clients/web/src/components/screens/PromptsScreen/PromptsScreen.test.tsx

@@ -1,7 +1,7 @@
 import { useState } from "react";
 import { describe, it, expect, vi } from "vitest";
 import userEvent from "@testing-library/user-event";
-import type { Prompt } from "@modelcontextprotocol/sdk/types.js";
+import type { Prompt } from "@modelcontextprotocol/client";
 import { renderWithMantine, screen } from "../../../test/renderWithMantine";
 import {
   PromptsScreen,

clients/web/src/components/screens/PromptsScreen/PromptsScreen.tsx

@@ -8,10 +8,7 @@ import {
   Stack,
   Text,
 } from "@mantine/core";
-import type {
-  GetPromptResult,
-  Prompt,
-} from "@modelcontextprotocol/sdk/types.js";
+import type { GetPromptResult, Prompt } from "@modelcontextprotocol/client";
 import { PromptControls } from "../../groups/PromptControls/PromptControls";
 import { PromptArgumentsForm } from "../../groups/PromptArgumentsForm/PromptArgumentsForm";
 import { PromptMessagesDisplay } from "../../groups/PromptMessagesDisplay/PromptMessagesDisplay";

clients/web/src/components/screens/ResourcesScreen/ResourcesScreen.stories.tsx

@@ -3,8 +3,8 @@ import type { ComponentProps } from "react";
 import type { Meta, StoryObj } from "@storybook/react-vite";
 import type {
   Resource,
-  ResourceTemplate,
-} from "@modelcontextprotocol/sdk/types.js";
+  ResourceTemplateType as ResourceTemplate,
+} from "@modelcontextprotocol/client";
 import type { InspectorResourceSubscription } from "../../../../../../core/mcp/types.js";
 import { expect, fn, userEvent, within } from "storybook/test";
 import { ResourcesScreen } from "./ResourcesScreen";

clients/web/src/components/screens/ResourcesScreen/ResourcesScreen.test.tsx

@@ -3,9 +3,9 @@ import { describe, it, expect, vi } from "vitest";
 import userEvent from "@testing-library/user-event";
 import type {
   Resource,
-  ResourceTemplate,
+  ResourceTemplateType as ResourceTemplate,
   ReadResourceResult,
-} from "@modelcontextprotocol/sdk/types.js";
+} from "@modelcontextprotocol/client";
 import { renderWithMantine, screen } from "../../../test/renderWithMantine";
 import {
   ResourcesScreen,

clients/web/src/components/screens/ResourcesScreen/ResourcesScreen.tsx

@@ -11,8 +11,8 @@ import {
 import type {
   ReadResourceResult,
   Resource,
-  ResourceTemplate,
-} from "@modelcontextprotocol/sdk/types.js";
+  ResourceTemplateType as ResourceTemplate,
+} from "@modelcontextprotocol/client";
 import type { InspectorResourceSubscription } from "../../../../../../core/mcp/types.js";
 import { ResourceControls } from "../../groups/ResourceControls/ResourceControls";
 import { ResourcePreviewPanel } from "../../groups/ResourcePreviewPanel/ResourcePreviewPanel";

clients/web/src/components/screens/TasksScreen/TasksScreen.stories.tsx

@@ -1,5 +1,5 @@
 import type { Meta, StoryObj } from "@storybook/react-vite";
-import type { Task } from "@modelcontextprotocol/sdk/types.js";
+import type { Task } from "@modelcontextprotocol/client";
 import { fn } from "storybook/test";
 import { TasksScreen } from "./TasksScreen";
 import { EMPTY_TASKS_UI } from "../screenUiState";

clients/web/src/components/screens/TasksScreen/TasksScreen.test.tsx

@@ -1,6 +1,6 @@
 import { describe, it, expect, vi } from "vitest";
 import userEvent from "@testing-library/user-event";
-import type { Task } from "@modelcontextprotocol/sdk/types.js";
+import type { Task } from "@modelcontextprotocol/client";
 import { renderWithMantine, screen } from "../../../test/renderWithMantine";
 import { TasksScreen } from "./TasksScreen";
 import { EMPTY_TASKS_UI } from "../screenUiState";

clients/web/src/components/screens/TasksScreen/TasksScreen.tsx

@@ -1,5 +1,5 @@
 import { Card, Flex, Stack } from "@mantine/core";
-import type { Task, TaskStatus } from "@modelcontextprotocol/sdk/types.js";
+import type { Task, TaskStatus } from "@modelcontextprotocol/client";
 import { TaskControls } from "../../groups/TaskControls/TaskControls";
 import { TaskListPanel } from "../../groups/TaskListPanel/TaskListPanel";
 import type { TaskProgress } from "../../groups/TaskCard/TaskCard";

clients/web/src/components/screens/ToolsScreen/ToolsScreen.fixtures.ts

@@ -1,4 +1,4 @@
-import type { Tool } from "@modelcontextprotocol/sdk/types.js";
+import type { Tool } from "@modelcontextprotocol/client";
 
 export const longToolList: Tool[] = [
   {

clients/web/src/components/screens/ToolsScreen/ToolsScreen.stories.tsx

@@ -1,7 +1,7 @@
 import { useState } from "react";
 import type { ComponentProps } from "react";
 import type { Meta, StoryObj } from "@storybook/react-vite";
-import type { ElicitRequest, Tool } from "@modelcontextprotocol/sdk/types.js";
+import type { ElicitRequest, Tool } from "@modelcontextprotocol/client";
 import { Modal } from "@mantine/core";
 import { fn, userEvent, within } from "storybook/test";
 import { ToolsScreen } from "./ToolsScreen";

clients/web/src/components/screens/ToolsScreen/ToolsScreen.test.tsx

@@ -1,7 +1,7 @@
 import { useState } from "react";
 import { describe, it, expect, vi } from "vitest";
 import userEvent from "@testing-library/user-event";
-import type { Tool } from "@modelcontextprotocol/sdk/types.js";
+import type { Tool } from "@modelcontextprotocol/client";
 import { renderWithMantine, screen } from "../../../test/renderWithMantine";
 import {
   ToolsScreen,

clients/web/src/components/screens/ToolsScreen/ToolsScreen.tsx

@@ -3,14 +3,14 @@ import type {
   CallToolResult,
   ReadResourceResult,
   Tool,
-} from "@modelcontextprotocol/sdk/types.js";
+} from "@modelcontextprotocol/client";
 import { ToolControls } from "../../groups/ToolControls/ToolControls";
 import {
   ToolDetailPanel,
   type ToolProgress,
 } from "../../groups/ToolDetailPanel/ToolDetailPanel";
 import { ToolResultPanel } from "../../groups/ToolResultPanel/ToolResultPanel";
-import { collectSchemaDefaults } from "../../../utils/jsonUtils";
+import { collectSchemaDefaults, toFormSchema } from "../../../utils/jsonUtils";
 
 export interface ToolCallState {
   status: "idle" | "pending" | "ok" | "error";
@@ -162,7 +162,10 @@ export function ToolsScreen({
               // empty-object fallback is an unreachable defensive default.
               let formValues: Record<string, unknown> = {};
               /* v8 ignore next -- unreachable: onSelectTool always names a tool in the list */
-              if (tool) formValues = collectSchemaDefaults(tool.inputSchema);
+              if (tool)
+                formValues = collectSchemaDefaults(
+                  toFormSchema(tool.inputSchema) ?? {},
+                );
               onUiChange({
                 ...ui,
                 selectedToolName: name,