fix: include the PoX sunset burn in mainnet staking reward totals

src/api/routes/v3/staking-rewards.ts

@@ -1,9 +1,17 @@
 import { FastifyPluginAsync } from 'fastify';
 import { Server } from 'node:http';
 import { TypeBoxTypeProvider } from '@fastify/type-provider-typebox';
+import { STACKS_MAINNET } from '@stacks/network';
 import { handleBurnchainChainTipCache } from '../../controllers/cache-controller.js';
 import { StakingRewardsSchema } from '../../schemas/v3/entities/staking-rewards.js';
 
+/**
+ * BTC burned on mainnet by the 2.0-era PoX sunset-ramp surcharge (bitcoin blocks ~766050-781551),
+ * in satoshis. The node never reported these burns in its burn block events, so they are added as a
+ * fixed historical total.
+ */
+const MAINNET_SUNSET_BURN_AMOUNT = 489352064n;
+
 export const StakingRewardsRoutes: FastifyPluginAsync<
   Record<never, never>,
   Server,
@@ -28,11 +36,15 @@ export const StakingRewardsRoutes: FastifyPluginAsync<
     },
     async (_req, reply) => {
       const totals = await fastify.db.v3.getStakingRewards();
+      const sunsetBurnAmount =
+        fastify.chainId === STACKS_MAINNET.chainId ? MAINNET_SUNSET_BURN_AMOUNT : 0n;
+      const rewardAmount = BigInt(totals.reward_amount);
+      const burnAmount = BigInt(totals.burn_amount) + sunsetBurnAmount;
       await reply.send({
         btc: {
-          reward_amount: totals.reward_amount,
-          burn_amount: totals.burn_amount,
-          total_amount: (BigInt(totals.reward_amount) + BigInt(totals.burn_amount)).toString(),
+          reward_amount: rewardAmount.toString(),
+          burn_amount: burnAmount.toString(),
+          total_amount: (rewardAmount + burnAmount).toString(),
         },
       });
     }

tests/api/burnchain/staking-rewards.test.ts

@@ -1,7 +1,7 @@
 import supertest from 'supertest';
 import { afterEach, beforeEach, describe, test } from 'node:test';
 import assert from 'node:assert/strict';
-import { STACKS_TESTNET } from '@stacks/network';
+import { STACKS_MAINNET, STACKS_TESTNET } from '@stacks/network';
 import { ApiServer, startApiServer } from '../../../src/api/init.ts';
 import { EventStreamServer, startEventServer } from '../../../src/event-stream/event-server.ts';
 import { httpPostRequest } from '../../../src/helpers.ts';
@@ -182,6 +182,19 @@ describe('staking rewards totals', () => {
     });
   });
 
+  test('mainnet totals include the fixed PoX sunset burn', async () => {
+    await api.terminate();
+    api = await startApiServer({ datastore: db, chainId: STACKS_MAINNET.chainId });
+    assert.deepEqual(await getTotals(), {
+      btc: { reward_amount: '0', burn_amount: '489352064', total_amount: '489352064' },
+    });
+
+    await deliverBurnBlock({ hash: '0xaa01', height: 100, burnAmount: 500n, rewardAmount: 1000n });
+    assert.deepEqual(await getTotals(), {
+      btc: { reward_amount: '1000', burn_amount: '489352564', total_amount: '489353564' },
+    });
+  });
+
   test('migration backfill reproduces the live counters', async () => {
     const migrationName = '1779800000016_chain-tip-staking-rewards';
     await deliverBurnBlock({ hash: '0xaa01', height: 100, burnAmount: 500n, rewardAmount: 1000n });