refactor!: extract LegacyServer/LegacyClient; NEW Server/Client compose them#2134
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refactor!: extract LegacyServer/LegacyClient; NEW Server/Client compose them#2134felixweinberger wants to merge 5 commits into
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git mv server.ts legacyServer.ts + class rename. Zero body changes. Importers updated to `LegacyServer as Server` so behavior is identical and the rename shows as a true file rename in history.
…rver `Server` no longer extends `Protocol`. It owns the 2026 stateless dispatch path (subscriptions, statelessHandlers, _dispatchStateless, _buildDispatchServerContext, _ondiscover) and the dual-mode surface (connect/close/transport/onclose/onerror, _fanoutNotify, send*ListChanged), lifted verbatim from the sectioned `LegacyServer` with field reads re-pointed at `this.config.*` / `this._legacy.*`. `LegacyServer` keeps the session-dependent block. Both share one handler registry via `_legacy._dispatch`/`_legacy.setRequestHandler`. `server.legacy` is the explicit escape hatch. LegacyServer body changes are limited to: - `_assertSession()` guard inserted at top of createMessage / elicitInput / listRoots / sendLoggingMessage / ping - ctor: dropped `subscriptions` init + `server/discover` registration (lifted to NEW Server) Adds `SdkErrorCode.SessionRequired`.
git mv client.ts legacyClient.ts + class rename. Zero body changes. Importers updated to `LegacyClient as Client` so behavior is identical and the rename shows as a true file rename in history.
…ient `Client` no longer extends `Protocol`. It owns the 2026 stateless send path (_isStateless/_buildMeta/_withMeta/_collect/_send/_negotiate/ subscribe/_listChangedLoop) and the typed request methods (callTool/listTools/getPrompt/listPrompts/readResource/listResources/ listResourceTemplates/complete/setLoggingLevel), lifted verbatim from the sectioned `LegacyClient` with field reads re-pointed at `this.config.*` / `this._legacy.*`. `LegacyClient` keeps the session-dependent block. Both share one handler registry via `_legacy._dispatch`/`_legacy.setRequestHandler`; negotiated server state lives on `_legacy` (single source of truth) and is written by both `_negotiate` (via `_setNegotiated`) and `_initialize`. `client.legacy` is the explicit escape hatch. LegacyClient body changes are limited to: - `_assertSession()` guard inserted at top of ping / subscribeResource / unsubscribeResource / sendRootsListChanged - ctor: dropped now-unused `_enforceStrictCapabilities` / `_pendingListChangedConfig` / `_cachedToolOutputValidators` fields (lifted to NEW Client) - `_initialize` / `_setupListChangedHandler` visibility widened to @internal
Integration tests that exercise the pre-2026 session-dependent surface (server.createMessage / elicitInput / listRoots / sendLoggingMessage / ping / getClientCapabilities / getClientVersion / oninitialized / createElicitationCompletionNotifier / notification / request / setNotificationHandler; client.sendRootsListChanged / ping / subscribeResource / unsubscribeResource / request / notification) now go through `.legacy`. LegacyTestClient unchanged: it extends NEW Client and pins versions, so `connect()` skips the discover probe exactly as before. clientSend statelessClient() helper updated to set `_transport` / negotiated state on `c.legacy` (private state moved there).
felixweinberger
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@modelcontextprotocol/client
@modelcontextprotocol/server
@modelcontextprotocol/express
@modelcontextprotocol/fastify
@modelcontextprotocol/hono
@modelcontextprotocol/node
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This was referenced May 20, 2026
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Extracts
LegacyServer/LegacyClient(theProtocol-derived, session-stateful classes) and introduces NEWServer/Clientthat own the 2026 stateless path and compose the legacy class via.legacy.Motivation and Context
After #2131 the sectioned
Server/Clientcarry both the 2026 stateless surface and the pre-2026 session-dependent surface side by side. That works, but nothing in the type system tells a caller which methods are session-only. This PR makes the boundary structural:Server/Clientno longer extendProtocol. They expose the 2026 stateless surface plus the version-agnostic typed request methods.createMessage/elicitInput/listRoots/sendLoggingMessage/pingon the server;subscribeResource/unsubscribeResource/sendRootsListChanged/pingon the client; rawrequest/notification/setNotificationHandleron both) live only onLegacyServer/LegacyClient, reachable via the explicit.legacyescape hatch._assertSession()guards the legacy methods at runtime and throwsSdkErrorCode.SessionRequiredwith a migration URL when called on a 2026 connection.Both classes share one handler registry and negotiated state (single source of truth on the legacy instance), so behavior is identical to the sectioned base; this PR just moves the seam into the type system.
How Has This Been Tested?
pnpm typecheck:all && lint:fix:all && build:all && test:all && docs:checkall green. Integration tests updated to call session-dependent methods through.legacy.Breaking Changes
Server/Clientno longer extendProtocol. Session-dependent methods move to.legacy.*. Seedocs/migration.md.Types of changes
Checklist
Additional context
Reviewable per-commit:
refactor(server): rename Server -> LegacyServer (verbatim)—git mv+ class rename, zero body changesrefactor(server)!: NEW Server class (Protocol-free) composes LegacyServerrefactor(client): rename Client -> LegacyClient (verbatim)—git mv+ class rename, zero body changesrefactor(client)!: NEW Client class (Protocol-free) composes LegacyClienttest: adapt tests to .legacy getter for session-dependent methods