feat(commands): add 'rs gain' to grant the VIP audio gain boost

Admins can now run 'rs gain list|grant <vip>|revoke <vip>' from web chat or
Discord. Grant matches only against the verified list and revoke only
against current holders, so a nickname shared with an unverified visitor
reports not-found rather than resolving to someone ineligible. The action
joins the moderation set so lockdown narrows it to lockdown admins.

Also extracts the ceiling math into audioLevelsService/gainMath.js and
covers both it and the command with node:test suites.

Co-Authored-By: Claude <noreply@anthropic.com>

server/src/services/operatorCommandService/commands/gain.test.js

@@ -0,0 +1,125 @@
+// Operator Gain Command Tests
+// Purpose: Verifies the audio gain boost command stays admin-only and VIP-only.
+// Scope: Exercises command target resolution with in-memory identity doubles.
+const test = require('node:test');
+const assert = require('node:assert/strict');
+const { createGainCommand } = require('./gain');
+
+const VIPS = [
+  { userId: 'usr-vip', nickname: 'Croissant', cookieUserId: 'cookie-croissant' },
+  { userId: 'usr-other', nickname: 'Baguette', cookieUserId: 'cookie-baguette' },
+];
+
+function createHarness({ verified = VIPS, boosted = [], isAdmin = true } = {}) {
+  const calls = [];
+  const replies = [];
+  const handler = createGainCommand({
+    listVerifiedUsers: () => verified,
+    listAudioGainBoostUsers: () => boosted,
+    grantAudioGainBoost: (selector, actor) => {
+      calls.push({ action: 'grant', selector, actor });
+      return { nickname: 'Croissant', cookieUserId: 'cookie-croissant' };
+    },
+    revokeAudioGainBoost: (selector, actor) => {
+      calls.push({ action: 'revoke', selector, actor });
+      return { nickname: 'Croissant', cookieUserId: 'cookie-croissant' };
+    },
+    sanitizeMentions: (value) => value,
+    config: { commands: { prefix: 'rs' } },
+  });
+  const message = {
+    actor: { id: 'admin', isAdmin },
+    reply: async (payload) => {
+      replies.push(payload);
+      return payload;
+    },
+  };
+  return { handler, message, calls, replies };
+}
+
+test('non-admins cannot manage the boost', async () => {
+  const { handler, message, calls, replies } = createHarness({ isAdmin: false });
+
+  await handler(message, ['grant', 'Croissant']);
+
+  assert.deepEqual(calls, []);
+  assert.match(replies[0].content, /Only admins/);
+});
+
+test('grant resolves a VIP nickname to its stable user id', async () => {
+  const { handler, message, calls } = createHarness();
+
+  await handler(message, ['grant', 'croissant']);
+
+  assert.deepEqual(calls, [{ action: 'grant', selector: 'usr-vip', actor: 'admin' }]);
+});
+
+test('grant refuses a nickname that belongs to no VIP', async () => {
+  const { handler, message, calls, replies } = createHarness({ verified: [] });
+
+  await handler(message, ['grant', 'Stranger']);
+
+  assert.deepEqual(calls, []);
+  assert.match(replies[0].content, /not found/i);
+});
+
+test('revoke only matches users who currently hold the boost', async () => {
+  const { handler, message, calls, replies } = createHarness({ boosted: [] });
+
+  await handler(message, ['revoke', 'Croissant']);
+
+  assert.deepEqual(calls, []);
+  assert.match(replies[0].content, /not found/i);
+});
+
+test('revoke resolves against the boosted list', async () => {
+  const { handler, message, calls } = createHarness({ boosted: [VIPS[0]] });
+
+  await handler(message, ['revoke', 'Croissant']);
+
+  assert.deepEqual(calls, [{ action: 'revoke', selector: 'usr-vip', actor: 'admin' }]);
+});
+
+test('grant without a target prints usage instead of acting', async () => {
+  const { handler, message, calls, replies } = createHarness();
+
+  await handler(message, ['grant']);
+
+  assert.deepEqual(calls, []);
+  assert.match(replies[0].content, /rs gain grant/);
+});
+
+test('list defaults when no subcommand is given', async () => {
+  const { handler, message, replies } = createHarness({ boosted: [VIPS[0]] });
+
+  await handler(message, []);
+
+  assert.match(replies[0].content, /Croissant/);
+  assert.match(replies[0].content, /usr-vip/);
+});
+
+test('list reports an empty holder set', async () => {
+  const { handler, message, replies } = createHarness({ boosted: [] });
+
+  await handler(message, ['list']);
+
+  assert.match(replies[0].content, /No users hold/);
+});
+
+test('a service rejection is surfaced instead of thrown', async () => {
+  const { handler, message, replies } = createHarness();
+  const failing = createGainCommand({
+    listVerifiedUsers: () => VIPS,
+    listAudioGainBoostUsers: () => [],
+    grantAudioGainBoost: () => {
+      throw new Error('Only verified VIPs can be granted an audio gain boost.');
+    },
+    revokeAudioGainBoost: () => null,
+    sanitizeMentions: (value) => value,
+    config: { commands: { prefix: 'rs' } },
+  });
+
+  await failing(message, ['grant', 'Croissant']);
+
+  assert.match(replies[0].content, /Only verified VIPs/);
+});