fix(proxy): stabilize upstream fetch transport

Refs #1686

tests/integration/proxy/fixtures/runtime-probe.cjs

@@ -0,0 +1,100 @@
+const http = require('node:http');
+const path = require('node:path');
+
+const repoRoot = process.env.CCS_RUNTIME_PROBE_ROOT || process.cwd();
+const {
+  closeOpenAICompatProxyServer,
+  startOpenAICompatProxyServer,
+} = require(path.join(repoRoot, 'dist/proxy/server/proxy-server.js'));
+
+function waitForListening(server) {
+  if (server.listening) return Promise.resolve();
+  return new Promise((resolve, reject) => {
+    server.once('error', reject);
+    server.once('listening', resolve);
+  });
+}
+
+function request(port, requestPath, options = {}) {
+  return new Promise((resolve, reject) => {
+    const req = http.request(
+      {
+        hostname: '127.0.0.1',
+        port,
+        path: requestPath,
+        method: options.method || 'GET',
+        headers: options.headers,
+        agent: options.agent,
+      },
+      (res) => {
+        let body = '';
+        res.setEncoding('utf8');
+        res.on('data', (chunk) => (body += chunk));
+        res.on('end', () => resolve({ status: res.statusCode || 0, body }));
+      }
+    );
+    req.once('error', reject);
+    req.end(options.body);
+  });
+}
+
+async function startProbeServer() {
+  const server = startOpenAICompatProxyServer({
+    profile: {
+      profileName: 'sentinel',
+      settingsPath: '/tmp/sentinel.settings.json',
+      baseUrl: process.env.CCS_RUNTIME_PROBE_UPSTREAM,
+      apiKey: 'sentinel-api-key-not-real',
+      provider: 'generic-chat-completion-api',
+      model: 'sentinel-model',
+      passthrough: false,
+    },
+    port: 0,
+    authToken: 'sentinel-local-token',
+  });
+  await waitForListening(server);
+  return server;
+}
+
+async function runTransportProbe() {
+  const server = await startProbeServer();
+  const port = server.address().port;
+  const response = await request(port, '/v1/messages', {
+    method: 'POST',
+    headers: {
+      'content-type': 'application/json',
+      'x-api-key': 'sentinel-local-token',
+    },
+    body: JSON.stringify({
+      model: 'sentinel-model',
+      messages: [{ role: 'user', content: 'hi' }],
+    }),
+  });
+  await closeOpenAICompatProxyServer(server, 250);
+  const parsed = JSON.parse(response.body);
+  console.log(
+    JSON.stringify({
+      status: response.status,
+      text: parsed.content?.[0]?.text,
+      error: parsed.error?.message,
+    })
+  );
+}
+
+async function runShutdownProbe() {
+  const server = await startProbeServer();
+  const port = server.address().port;
+  const agent = new http.Agent({ keepAlive: true });
+  await request(port, '/health', { agent });
+  const startedAt = Date.now();
+  await closeOpenAICompatProxyServer(server, 250);
+  const elapsedMs = Date.now() - startedAt;
+  agent.destroy();
+  console.log(JSON.stringify({ closed: !server.listening, elapsedMs }));
+}
+
+const mode = process.env.CCS_RUNTIME_PROBE_MODE || 'transport';
+Promise.resolve(mode === 'shutdown' ? runShutdownProbe() : runTransportProbe()).catch((error) => {
+  console.error(JSON.stringify({ name: error.name, message: error.message }));
+  process.exitCode = 1;
+});