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>
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