initial: @a2a/mcp gateway for a2acloud agents

Local MCP server that exposes any number of deployed A2A agents to
Claude Code, Cursor, Windsurf, and other MCP clients. Reuses the
~/.a2a/credentials.json token written by the Python a2a CLI. Adding
or removing agents is a single ~/.a2a/mcp.json edit.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/credentials.ts

@@ -0,0 +1,61 @@
+/**
+ * Reader for ~/.a2a/credentials.json — same file the Python `a2a` CLI writes.
+ *
+ * We deliberately *only read* this file (and overwrite it on `a2a-mcp login`)
+ * so a single login flow is shared between the Python and Node tooling.
+ */
+import { promises as fs } from "node:fs";
+import os from "node:os";
+import path from "node:path";
+
+export const DEFAULT_API_URL = "https://api.a2acloud.io";
+
+export interface Credentials {
+  apiUrl: string;
+  token: string;
+  email: string;
+}
+
+const credsDir = () => path.join(os.homedir(), ".a2a");
+const credsFile = () => path.join(credsDir(), "credentials.json");
+
+export async function loadCredentials(): Promise<Credentials | null> {
+  try {
+    const raw = await fs.readFile(credsFile(), "utf8");
+    const data = JSON.parse(raw);
+    if (!data?.token) return null;
+    return {
+      apiUrl: data.api_url ?? DEFAULT_API_URL,
+      token: data.token,
+      email: data.email ?? "",
+    };
+  } catch (err: any) {
+    if (err?.code === "ENOENT") return null;
+    throw err;
+  }
+}
+
+export async function saveCredentials(c: Credentials): Promise<void> {
+  await fs.mkdir(credsDir(), { recursive: true });
+  await fs.writeFile(
+    credsFile(),
+    JSON.stringify({ api_url: c.apiUrl, token: c.token, email: c.email }),
+    { mode: 0o600 },
+  );
+}
+
+export async function clearCredentials(): Promise<boolean> {
+  try {
+    await fs.unlink(credsFile());
+    return true;
+  } catch (err: any) {
+    if (err?.code === "ENOENT") return false;
+    throw err;
+  }
+}
+
+export function resolveApiUrl(override?: string): string {
+  if (override) return override;
+  if (process.env.A2A_API_URL) return process.env.A2A_API_URL;
+  return DEFAULT_API_URL;
+}