fix: keep sse streams alive behind proxies

test/fetch-utils.test.mjs

@@ -1,5 +1,6 @@
 import test from 'node:test';
 import assert from 'node:assert/strict';
+import { readFileSync } from 'node:fs';
 import { safeFetch, safeFetchText, getFetchMetrics } from '../apis/utils/fetch.mjs';
 
 test('safeFetch reports HTML as degraded JSON response', async () => {
@@ -34,3 +35,14 @@ test('safeFetchText returns text and byte count', async () => {
     globalThis.fetch = originalFetch;
   }
 });
+
+test('SSE endpoint sends reconnect guidance and clears heartbeat timer', () => {
+  const server = readFileSync(new URL('../server.mjs', import.meta.url), 'utf8');
+  const config = readFileSync(new URL('../crucix.config.mjs', import.meta.url), 'utf8');
+  assert.match(config, /sseHeartbeatIntervalMs/);
+  assert.match(server, /retry: 10000\\n/);
+  assert.match(server, /setInterval\(\(\) =>/);
+  assert.match(server, /: heartbeat/);
+  assert.match(server, /clearInterval\(heartbeat\)/);
+  assert.match(server, /X-Accel-Buffering/);
+});