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/config.ts

@@ -0,0 +1,62 @@
+/**
+ * Local config at ~/.a2a/mcp.json — which agents the gateway should expose.
+ *
+ * We store the agent URL alongside the name so the gateway never needs to hit
+ * the control plane during startup. Adding/removing an agent is a single
+ * file write; the MCP client picks up the change on the next list_tools.
+ */
+import { promises as fs } from "node:fs";
+import os from "node:os";
+import path from "node:path";
+
+export interface EnabledAgent {
+  name: string;
+  url: string;
+  description?: string;
+  addedAt: string;
+}
+
+export interface GatewayConfig {
+  version: 1;
+  agents: EnabledAgent[];
+}
+
+const cfgDir = () => path.join(os.homedir(), ".a2a");
+const cfgFile = () => path.join(cfgDir(), "mcp.json");
+
+const EMPTY: GatewayConfig = { version: 1, agents: [] };
+
+export async function loadConfig(): Promise<GatewayConfig> {
+  try {
+    const raw = await fs.readFile(cfgFile(), "utf8");
+    const data = JSON.parse(raw);
+    if (data?.version !== 1 || !Array.isArray(data.agents)) return { ...EMPTY };
+    return data as GatewayConfig;
+  } catch (err: any) {
+    if (err?.code === "ENOENT") return { ...EMPTY };
+    throw err;
+  }
+}
+
+export async function saveConfig(cfg: GatewayConfig): Promise<void> {
+  await fs.mkdir(cfgDir(), { recursive: true });
+  await fs.writeFile(cfgFile(), JSON.stringify(cfg, null, 2), { mode: 0o600 });
+}
+
+export async function addAgent(agent: EnabledAgent): Promise<GatewayConfig> {
+  const cfg = await loadConfig();
+  const existing = cfg.agents.findIndex((a) => a.name === agent.name);
+  if (existing >= 0) cfg.agents[existing] = agent;
+  else cfg.agents.push(agent);
+  await saveConfig(cfg);
+  return cfg;
+}
+
+export async function removeAgent(name: string): Promise<boolean> {
+  const cfg = await loadConfig();
+  const before = cfg.agents.length;
+  cfg.agents = cfg.agents.filter((a) => a.name !== name);
+  if (cfg.agents.length === before) return false;
+  await saveConfig(cfg);
+  return true;
+}