[WIP] Add experimental HTTP backend SPI

package.json

@@ -72,6 +72,11 @@
       "import": "./dist/transports/server.js",
       "default": "./dist/transports/server.js"
     },
+    "./experimental/http-backend": {
+      "types": "./dist/transports/http-backend.d.ts",
+      "import": "./dist/transports/http-backend.js",
+      "default": "./dist/transports/http-backend.js"
+    },
     "./experimental/node": {
       "types": "./dist/transports/node-adapter.d.ts",
       "import": "./dist/transports/node-adapter.js",

src/core/jsonrpc.ts

@@ -432,6 +432,15 @@ type PreparedRequest<Output> = {
  */
 export type MaybePromise<T> = T | Promise<T>;
 
+/**
+ * Allocates IDs for JSON-RPC requests sent by this connection.
+ *
+ * The default generator is a per-connection numeric sequence starting at `0`.
+ * HTTP server integrations can inject a custom generator so server-originated
+ * request IDs remain unique across distributed server instances.
+ */
+export type JsonRpcRequestIdGenerator = () => string | number;
+
 /**
  * Incoming request passed to JSON-RPC handlers.
  */
@@ -852,6 +861,13 @@ export type ConnectionOptions = {
    * @internal
    */
   allowBatches?: boolean;
+
+  /**
+   * Allocates IDs for outbound JSON-RPC requests.
+   *
+   * Defaults to the existing per-connection numeric sequence: 0, 1, 2, ...
+   */
+  requestIdGenerator?: JsonRpcRequestIdGenerator;
 };
 
 /**
@@ -865,6 +881,8 @@ export class Connection {
     new Map();
   private incomingRequests: Map<JsonRpcId, AbortController> = new Map();
   private nextRequestId = 0;
+  private requestIdGenerator: JsonRpcRequestIdGenerator = () =>
+    this.nextRequestId++;
   private staticHandlers: JsonRpcHandler[] = [];
   private dynamicHandlers: Set<JsonRpcHandler> = new Set();
   private fallbackHandlers: JsonRpcHandler[] = [];
@@ -1115,7 +1133,7 @@ export class Connection {
     mapResponse: ((response: Resp) => Output) | undefined,
     options: SendRequestOptions = {},
   ): PreparedRequest<Output> {
-    const id = this.nextRequestId++;
+    const id = this.requestIdGenerator();
     let cancel = () => {};
     const response = new Promise<Output>((resolve, reject) => {
       const pendingResponse: ConnectionPendingResponse = {
@@ -1189,6 +1207,8 @@ export class Connection {
     this.staticHandlers = handlers;
     this.fallbackHandlers = [...(options?.fallbackHandlers ?? [])];
     this.allowBatches = options?.allowBatches ?? true;
+    this.requestIdGenerator =
+      options?.requestIdGenerator ?? (() => this.nextRequestId++);
     this.closedPromise = new Promise((resolve) => {
       this.abortController.signal.addEventListener("abort", () => resolve());
     });

src/test-support/test-http-server.ts

@@ -1,3 +1,4 @@
+import type { AcpHttpBackend } from "../transports/http-backend.js";
 import http from "node:http";
 import { WebSocketServer } from "ws";
 
@@ -19,9 +20,12 @@ export interface TestHttpServer {
 
 export async function startTestServer(
   createAgent: () => AgentApp = () => createTestAgentApp(),
-  options: { port?: number } = {},
+  options: { port?: number; httpBackend?: AcpHttpBackend } = {},
 ): Promise<TestHttpServer> {
-  const acpServer = new AcpServer({ createAgent });
+  const acpServer = new AcpServer({
+    createAgent,
+    httpBackend: options.httpBackend,
+  });
   const httpServer = http.createServer(createNodeHttpHandler(acpServer));
   const webSocketServer = new WebSocketServer({ noServer: true });