diff --git a/scripts/ci/lib/app-harness.js b/scripts/ci/lib/app-harness.js
index 1fe3bc29..c5c41acd 100644
--- a/scripts/ci/lib/app-harness.js
+++ b/scripts/ci/lib/app-harness.js
@@ -133,6 +133,29 @@ function parsePerfMarks(log) {
   return marks;
 }
 
+// Pure verdict on a backend.log: the log-based half of the boot check (provenance
+// matches HEAD, the three perf marks exist, are ordered, and are not degenerate).
+// Kept pure + exported so it can be mutation-tested (selftest-gate.js feeds it
+// crafted broken logs and proves each guard fires) without launching the app.
+// Returns { failures: string[], sha, marks }; empty failures == the log half passed.
+function bootFailures({ log, headShort } = {}) {
+  const failures = [];
+  const sha = parseProvenanceSha(log || '');
+  if (!sha) failures.push('no [provenance] line in backend.log');
+  else if (headShort && sha !== headShort) failures.push(`provenance sha ${sha} != git HEAD ${headShort}`);
+
+  const marks = parsePerfMarks(log || '');
+  const missing = ['app-launch', 'first-paint', 'backend-http-ready'].filter((k) => !(k in marks));
+  if (missing.length) missing.forEach((k) => failures.push(`missing [perf] ${k}`));
+  else {
+    if (!(marks['app-launch'] <= marks['first-paint'] && marks['first-paint'] <= marks['backend-http-ready'])) {
+      failures.push(`[perf] marks out of order: ${JSON.stringify(marks)}`);
+    }
+    if (!(marks['backend-http-ready'] > 0)) failures.push('[perf] backend-http-ready not > 0 (degenerate marks)');
+  }
+  return { failures, sha, marks };
+}
+
 // Launch the app and poll its backend.log until it reports HTTP-ready (or time out).
 // Returns { child, log, port }. Caller is responsible for killApp(child).
 async function launchAndWait({ appPath, timeoutMs = 180000, freshLog = true } = {}) {
@@ -175,5 +198,6 @@ module.exports = {
   attachToRunning,
   parseProvenanceSha,
   parsePerfMarks,
+  bootFailures,
   launchAndWait,
 };
diff --git a/scripts/ci/selftest-gate.js b/scripts/ci/selftest-gate.js
new file mode 100644
index 00000000..4cc90569
--- /dev/null
+++ b/scripts/ci/selftest-gate.js
@@ -0,0 +1,58 @@
+#!/usr/bin/env node
+// "Test the tests" - mutation testing of the gate's own logic. For each guard in
+// the boot check, we feed a deliberately BROKEN backend.log and assert the guard
+// fires (and that a good log passes). If breaking the input doesn't turn the gate
+// red, the gate is theater; this script fails loudly when that happens.
+//
+// This covers the PURE, log-based assertions (provenance + perf). The live-process
+// guards (signature --require-signed, wrong-token auth, verify-all aggregation,
+// renderer paint) are fault-injected separately - see GATE_AUDIT.md.
+//
+//   node scripts/ci/selftest-gate.js
+//
+// Exit 0 = every guard discriminates good from broken. Exit 1 = a guard is fake.
+
+'use strict';
+const h = require('./lib/app-harness');
+
+let failed = 0;
+function check(name, cond) { process.stdout.write(`  ${cond ? 'ok  ' : 'FAIL'}  ${name}\n`); if (!cond) failed++; }
+const caught = (log, head, re) => h.bootFailures({ log, headShort: head }).failures.some((f) => re.test(f));
+
+const HEAD = 'abc123def456';
+const GOOD = [
+  '[provenance] OpenSwarm 1.1.69 sha=abc123def456 channel=stable builtAt=2026-01-01T00:00:00Z',
+  '[perf] app-launch t=100',
+  '[perf] first-paint t=400',
+  '[perf] backend-http-ready t=4000',
+  'Backend ready on port 8324',
+].join('\n');
+
+process.stdout.write('boot-check mutation tests:\n');
+
+// Baseline: a good log must PASS (no false positives - the inverse failure mode).
+check('good log -> 0 failures (no false alarm)', h.bootFailures({ log: GOOD, headShort: HEAD }).failures.length === 0);
+
+// Each mutation must be CAUGHT:
+check('missing [provenance] -> caught', caught(GOOD.replace(/\[provenance\].*/, ''), HEAD, /provenance/));
+check('sha != HEAD -> caught', caught(GOOD.replace('abc123def456', '000000000000'), HEAD, /!= git HEAD/));
+check('missing first-paint mark -> caught', caught(GOOD.replace(/\[perf\] first-paint t=400\n/, ''), HEAD, /first-paint/));
+check('missing backend-http-ready mark -> caught', caught(GOOD.replace(/\[perf\] backend-http-ready t=4000/, ''), HEAD, /backend-http-ready/));
+check('out-of-order marks -> caught', caught(GOOD.replace('first-paint t=400', 'first-paint t=9999'), HEAD, /out of order/));
+check('degenerate all-zero marks -> caught', caught(
+  '[provenance] OpenSwarm 1 sha=abc123def456 channel=stable\n[perf] app-launch t=0\n[perf] first-paint t=0\n[perf] backend-http-ready t=0',
+  HEAD, /> 0|degenerate/));
+
+// And a stale build (old sha) must be caught even with all marks fine - the exact
+// real-world case we already saw fire live.
+check('stale build (every mark fine, wrong sha) -> still caught', caught(GOOD.replace('abc123def456', 'deadbeef0000'), HEAD, /!= git HEAD/));
+
+process.stdout.write('\nparse-function edge cases:\n');
+check('parseProvenanceSha reads a real line', h.parseProvenanceSha(GOOD) === 'abc123def456');
+check('parseProvenanceSha returns null on no marker', h.parseProvenanceSha('nothing here') === null);
+check('parsePerfMarks finds all three', Object.keys(h.parsePerfMarks(GOOD)).length === 3);
+
+process.stdout.write(failed
+  ? `\nGATE SELFTEST FAIL: ${failed} guard(s) did not discriminate - the gate has theater in it.\n`
+  : '\nGATE SELFTEST PASS: every boot guard fires on a break and passes on good input.\n');
+process.exit(failed ? 1 : 0);
diff --git a/scripts/ci/verify-packaged-app.js b/scripts/ci/verify-packaged-app.js
index 7cab0523..7a051757 100644
--- a/scripts/ci/verify-packaged-app.js
+++ b/scripts/ci/verify-packaged-app.js
@@ -41,16 +41,9 @@ async function main() {
   child = res.child;
   const { log, port } = res;
 
-  // --- assertions ---
-  const provSha = h.parseProvenanceSha(log);
-  if (!provSha) fail('no [provenance] line in backend.log (app may not have booted)');
-  if (headShort && provSha !== headShort) fail(`provenance sha ${provSha} != git HEAD ${headShort}`);
-
-  const marks = h.parsePerfMarks(log);
-  for (const k of ['app-launch', 'first-paint', 'backend-http-ready']) if (!(k in marks)) fail(`missing [perf] ${k} in backend.log`);
-  if (!(marks['app-launch'] <= marks['first-paint'] && marks['first-paint'] <= marks['backend-http-ready'])) {
-    fail(`[perf] marks out of order: ${JSON.stringify(marks)}`);
-  }
+  // --- assertions (log half is pure + mutation-tested in selftest-gate.js) ---
+  const { failures, sha: provSha, marks } = h.bootFailures({ log, headShort });
+  if (failures.length) fail(failures.join('; '));
 
   if (port) {
     let code = 0;