feat(backend): RpcClient (spawn/send/request/event) over JSONL

backend/src/rpc/rpc-client.ts

@@ -0,0 +1,38 @@
+import type { ChildProcessWithoutNullStreams } from "node:child_process";
+import { attachJsonlReader } from "./line-splitter.js";
+
+type Listener = (evt: any) => void;
+
+export class RpcClient {
+  private seq = 0;
+  private pending = new Map<string, (resp: any) => void>();
+  private listeners = new Set<Listener>();
+
+  constructor(private child: ChildProcessWithoutNullStreams) {
+    attachJsonlReader(child.stdout, (line) => {
+      if (!line) return;
+      let msg: any;
+      try { msg = JSON.parse(line); } catch { return; }
+      if (msg.type === "response" && msg.id && this.pending.has(msg.id)) {
+        this.pending.get(msg.id)!(msg);
+        this.pending.delete(msg.id);
+        return;
+      }
+      for (const l of this.listeners) l(msg);
+    });
+  }
+
+  nextId(): string { return `c${++this.seq}`; }
+
+  send(cmd: object): void { this.child.stdin.write(JSON.stringify(cmd) + "\n"); }
+
+  request(cmd: object & { type: string }): Promise<any> {
+    const id = this.nextId();
+    return new Promise((resolve) => {
+      this.pending.set(id, resolve);
+      this.send({ ...cmd, id });
+    });
+  }
+
+  on(_event: "event", cb: Listener): void { this.listeners.add(cb); }
+}

backend/test/rpc-client.test.ts

@@ -0,0 +1,26 @@
+import { test, expect } from "vitest";
+import { spawn } from "node:child_process";
+import path from "node:path";
+import { RpcClient } from "../src/rpc/rpc-client.js";
+
+const FAKE = path.resolve("../harness/tests/fake_pi/fake_pi_rpc.mjs");
+const SCRIPT = path.resolve("../harness/tests/fake_pi/scripts/f1_disambiguation.json");
+
+test("request(get_available_models) correla la response", async () => {
+  const child = spawn("node", [FAKE, SCRIPT]);
+  const rpc = new RpcClient(child as any);
+  const res = await rpc.request({ type: "get_available_models" });
+  expect(res.data.models[0].provider).toBe("zai");
+  child.stdin.end();
+});
+
+test("prompt emette un evento extension_ui_request", async () => {
+  const child = spawn("node", [FAKE, SCRIPT]);
+  const rpc = new RpcClient(child as any);
+  const got = new Promise<any>((resolve) => rpc.on("event", (e) => e.type === "extension_ui_request" && resolve(e)));
+  rpc.send({ type: "prompt", message: "/nuova-domanda \"x\"" });
+  const evt = await got;
+  expect(evt.method).toBe("input");                       // shape nativa di Pi
+  expect(JSON.parse(evt.title).widget).toBe("select");    // descriptor nel title
+  child.stdin.end();
+});