simplify: move RequestTransport/Backchannel2511 to internal-only; drop DispatchEnv alias

- core/public no longer exports RequestTransport or isRequestTransport
  (kept in the internal barrel; shttpHandler can be public without exposing
  the second transport interface before SEP-2598 settles).
- server no longer exports Backchannel2511 (constructed internally by
  shttpHandler/streamableHttp; it exists to be deleted when 2025-11 sunsets,
  so making it API surface defeats that).
- DispatchEnv deprecated alias deleted (RequestEnv is the name).
- Outbound was already not in public exports — confirmed unchanged.

Author: felixweinberger

packages/core/src/exports/public/index.ts

@@ -71,9 +71,10 @@ export { takeResult, toArrayAsync } from '../../shared/responseMessage.js';
 // stdio message framing utilities (for custom transport authors)
 export { deserializeMessage, ReadBuffer, serializeMessage } from '../../shared/stdio.js';
 
-// Transport types (NOT normalizeHeaders)
-export type { ChannelTransport, FetchLike, RequestTransport, Transport, TransportSendOptions } from '../../shared/transport.js';
-export { createFetchWithInit, isRequestTransport } from '../../shared/transport.js';
+// Transport types (NOT normalizeHeaders). RequestTransport stays internal until
+// SEP-2598 (pluggable transports) finalizes.
+export type { ChannelTransport, FetchLike, Transport, TransportSendOptions } from '../../shared/transport.js';
+export { createFetchWithInit } from '../../shared/transport.js';
 
 // URI Template
 export type { Variables } from '../../shared/uriTemplate.js';

packages/core/src/shared/dispatcher.ts

@@ -18,9 +18,6 @@ import { getNotificationSchema, getRequestSchema, ProtocolError, ProtocolErrorCo
 import type { StandardSchemaV1 } from '../util/standardSchema.js';
 import type { BaseContext, RequestEnv, RequestOptions } from './context.js';
 
-/** @deprecated Renamed to {@linkcode RequestEnv} (now in `context.ts`). */
-export type DispatchEnv = RequestEnv;
-
 /**
  * One yielded item from {@linkcode Dispatcher.dispatch}. A dispatch yields zero or more
  * notifications followed by exactly one terminal response.

packages/server/src/index.ts

@@ -6,7 +6,6 @@
 //
 // Any new export added here becomes public API. Use named exports, not wildcards.
 
-export { Backchannel2511 } from './server/backchannel2511.js';
 export { Server } from './server/compat.js';
 export type { CompletableSchema, CompleteCallback } from './server/completable.js';
 export { completable, isCompletable } from './server/completable.js';