diff --git a/scripts/ci/verify-preflight.js b/scripts/ci/verify-preflight.js
new file mode 100644
index 00000000..12f7746b
--- /dev/null
+++ b/scripts/ci/verify-preflight.js
@@ -0,0 +1,89 @@
+#!/usr/bin/env node
+// Layer 5: hostile-env matrix verifier. Reads OPENSWARM_TEST_NETWORK / _APPDATA / _LANG flags from the environment and asserts the preflight produces the EXPECTED verdict for that scenario. A false positive ('fail' under network=blocked instead of 'warn') is the bug class we are guarding against; this leg fails red when it happens. Pure node, no app launch, runs on every CI leg in under 10s.
+
+'use strict';
+const fs = require('fs');
+const os = require('os');
+const path = require('path');
+const pf = require('../../electron/preflight');
+
+function expectVerdict({ network, appdata, lang }) {
+  // Encode the matrix: each axis has known-expected ranges. 'fail' means a
+  // specific check returns fail; 'warn' means it returns warn (not fail);
+  // 'ok' means clean. Network-blocked must be WARN, not fail.
+  if (appdata === 'readonly') return { verdictRange: ['fail'], expect: { 'appdata-writable': 'fail' } };
+  if (network === 'blocked') return { verdictRange: ['warn'], expect: { network: 'warn', clock: 'warn' } };
+  if (lang === 'de-DE') return { verdictRange: ['ok', 'warn'], expect: {} };
+  return { verdictRange: ['ok', 'warn'], expect: {} };
+}
+
+async function main() {
+  const scenario = {
+    network: process.env.OPENSWARM_TEST_NETWORK || 'normal',
+    appdata: process.env.OPENSWARM_TEST_APPDATA || 'normal',
+    lang: process.env.OPENSWARM_TEST_LANG || 'en-US',
+  };
+  process.stdout.write(`Scenario: network=${scenario.network} appdata=${scenario.appdata} lang=${scenario.lang}\n`);
+
+  const env = pf.defaultEnv();
+  // Synthesize the hostile conditions inside env so we don't actually have to
+  // poison the runner's filesystem or DNS (and so the gate is hermetic).
+  if (scenario.network === 'blocked') {
+    // Block egress by routing through a hung local server.
+    const http = require('http');
+    const blockedSrv = http.createServer(() => { /* never respond */ });
+    await new Promise((resolve) => blockedSrv.listen(0, '127.0.0.1', resolve));
+    const blockedUrl = `http://127.0.0.1:${blockedSrv.address().port}/`;
+    process.on('exit', () => { try { blockedSrv.close(); } catch {} });
+    var netOpts = { url: blockedUrl, timeoutMs: 600 };
+    var clockOpts = { url: blockedUrl, timeoutMs: 600 };
+    var dsOpts = { host: 'invalid-host-that-cannot-resolve.openswarm.local', timeoutMs: 400 };
+  }
+  if (scenario.appdata === 'readonly') {
+    // Synthesize an unwriteable dir by overriding writeFileSync to throw.
+    env.fs = Object.assign({}, fs, { writeFileSync: () => { throw new Error('EACCES synthetic'); } });
+  }
+  if (scenario.lang === 'de-DE') {
+    // Pretend Get-MpComputerStatus returned a German antivirus name.
+    env.child_process = { execFile: (cmd, args, opts, cb) => setImmediate(() => cb(null, 'Antivirenprogramm aktiviert: True', '')) };
+    env.platform = 'win32';
+  }
+
+  const dataDir = path.join(os.tmpdir(), `openswarm-pf-scenario-${process.pid}-${Date.now()}`);
+  const t0 = Date.now();
+  const result = await pf.run(env, {
+    dataDir,
+    network: typeof netOpts !== 'undefined' ? netOpts : { url: 'https://api.openswarm.com/', timeoutMs: 4000 },
+    clock: typeof clockOpts !== 'undefined' ? clockOpts : undefined,
+    dualStack: typeof dsOpts !== 'undefined' ? dsOpts : undefined,
+  });
+  const dt = Date.now() - t0;
+  process.stdout.write(`Total runtime: ${dt}ms; verdict: ${result.verdict}\n`);
+
+  let failed = 0;
+  const expected = expectVerdict(scenario);
+  if (!expected.verdictRange.includes(result.verdict)) {
+    process.stderr.write(`  FAIL  verdict ${result.verdict} not in expected ${JSON.stringify(expected.verdictRange)}\n`);
+    failed++;
+  } else {
+    process.stdout.write(`  ok    verdict ${result.verdict} matches expectation\n`);
+  }
+  for (const [name, expStatus] of Object.entries(expected.expect)) {
+    const r = result.results.find((x) => x.name === name);
+    if (!r) { process.stderr.write(`  FAIL  no result for check ${name}\n`); failed++; continue; }
+    if (r.status !== expStatus) {
+      process.stderr.write(`  FAIL  ${name} status=${r.status} expected ${expStatus} (${r.reason})\n`);
+      failed++;
+    } else {
+      process.stdout.write(`  ok    ${name} = ${r.status} (${r.reason})\n`);
+    }
+  }
+  // Belt-and-braces: total runtime stays under a budget regardless of scenario.
+  if (dt > 10_000) { process.stderr.write(`  FAIL  preflight took ${dt}ms > 10s budget\n`); failed++; }
+
+  if (failed) { process.stderr.write(`\nPREFLIGHT MATRIX FAIL: ${failed} assertion(s)\n`); process.exit(1); }
+  process.stdout.write('\nPREFLIGHT MATRIX PASS: verdict matches the expected envelope for this scenario.\n');
+  process.exit(0);
+}
+
+main().catch((e) => { process.stderr.write(`\nPREFLIGHT MATRIX FAIL: ${e && e.stack || e}\n`); process.exit(1); });