feat(groups): add fail-closed admission management

packages/minecraft/src/index.ts

@@ -46,6 +46,46 @@ export function formatManagedDiscordNickname(
   return [...firstName.trim()].slice(0, DISCORD_NICKNAME_LIMIT).join("").trimEnd();
 }
 
+export interface DiscordGuildIdentity {
+  id: string;
+  username: string;
+  globalName: string | null;
+  nickname: string | null;
+}
+
+export async function getGuildMemberIdentity(
+  input: { guildId: string; discordUserId: string; botToken: string },
+  request: typeof fetch = fetch,
+): Promise<DiscordGuildIdentity> {
+  const response = await request(
+    `https://discord.com/api/v10/guilds/${input.guildId}/members/${input.discordUserId}`,
+    {
+      headers: {
+        authorization: `Bot ${input.botToken}`,
+        accept: "application/json",
+      },
+      cache: "no-store",
+    },
+  );
+  if (!response.ok) throw new Error(`Discord guild member lookup failed (${response.status})`);
+
+  const payload: unknown = await response.json();
+  if (!payload || typeof payload !== "object") throw new Error("Discord guild member lookup returned invalid data");
+  const member = payload as { nick?: unknown; user?: unknown };
+  if (!member.user || typeof member.user !== "object") throw new Error("Discord guild member lookup omitted user data");
+  const user = member.user as { id?: unknown; username?: unknown; global_name?: unknown };
+  if (typeof user.id !== "string" || typeof user.username !== "string") {
+    throw new Error("Discord guild member lookup returned invalid user data");
+  }
+
+  return {
+    id: user.id,
+    username: user.username,
+    globalName: typeof user.global_name === "string" ? user.global_name : null,
+    nickname: typeof member.nick === "string" ? member.nick : null,
+  };
+}
+
 export async function updateGuildNickname(
   input: {
     guildId: string;

packages/minecraft/test/discord.test.ts

@@ -1,5 +1,25 @@
 import { describe, expect, it, vi } from "vitest";
-import { updateGuildNickname } from "../src/index";
+import { getGuildMemberIdentity, updateGuildNickname } from "../src/index";
+
+describe("Discord guild identity", () => {
+  it("reads the member username, global name, nickname, and immutable ID", async () => {
+    const request = vi.fn<typeof fetch>().mockResolvedValue(new Response(JSON.stringify({
+      nick: "Sam (Notch)",
+      user: { id: "987654321098765432", username: "samcraft", global_name: "Sam" },
+    }), { status: 200, headers: { "content-type": "application/json" } }));
+
+    await expect(getGuildMemberIdentity({
+      guildId: "123456789012345678",
+      discordUserId: "987654321098765432",
+      botToken: "secret",
+    }, request)).resolves.toEqual({
+      id: "987654321098765432",
+      username: "samcraft",
+      globalName: "Sam",
+      nickname: "Sam (Notch)",
+    });
+  });
+});
 
 describe("Discord nickname updates", () => {
   it("updates a member in the configured guild using bot authentication", async () => {