diff --git a/test/back/process-failure.test.cjs b/test/back/process-failure.test.cjs
new file mode 100644
index 00000000..fb217887
--- /dev/null
+++ b/test/back/process-failure.test.cjs
@@ -0,0 +1,52 @@
+const assert = require('node:assert/strict');
+const { test } = require('node:test');
+const { processFailure } = require('../helpers/process-failure.cjs');
+
+test('process failure diagnostics classify native crashes without credentials or raw output', () => {
+  const secret = 'private-client-secret';
+  const summary = processFailure({
+    code: null,
+    signal: 'SIGTRAP',
+    killed: false,
+    cmd: `node worker.cjs ${secret}`,
+    message: secret,
+    stdout: JSON.stringify({ token: secret }),
+    stderr: `${secret}\nCheck failed: (data_) != nullptr.\ncompiler/heap-refs.h\nv8::internal::compiler::JSHeapBroker\n`,
+  });
+  assert.equal(JSON.stringify(summary).includes(secret), false);
+  assert.equal(summary.signal, 'SIGTRAP');
+  assert.equal(summary.fatal.v8Check, true);
+  assert.equal(summary.fatal.heapBroker, true);
+  assert.equal(summary.fatal.compiler, true);
+  assert.equal(summary.fatal.outOfMemory, false);
+  assert.equal(summary.fatal.threadCreation, false);
+});
+
+test('process failure diagnostics retain timeout and resource classes without arbitrary error fields', () => {
+  const runtime = { versions: { node: '24.21.0' }, arch: 'x64' };
+  const summary = processFailure(
+    {
+      code: 1,
+      signal: 'SIGTERM private-token',
+      killed: true,
+      stderr: 'pthread_create: resource unavailable; heap out of memory',
+    },
+    runtime,
+  );
+  assert.deepEqual(summary, {
+    code: 1,
+    signal: null,
+    killed: true,
+    node: '24.21.0',
+    arch: 'x64',
+    fatal: {
+      threadCreation: true,
+      outOfMemory: true,
+      v8Check: false,
+      heapBroker: false,
+      compiler: false,
+    },
+  });
+  assert.equal(processFailure({ code: 'private-token' }).code, null);
+  assert.equal(processFailure().signal, null);
+});
diff --git a/test/back/systemTokenRenewal.test.cjs b/test/back/systemTokenRenewal.test.cjs
index 5e70be50..c807a5f3 100644
--- a/test/back/systemTokenRenewal.test.cjs
+++ b/test/back/systemTokenRenewal.test.cjs
@@ -7,6 +7,7 @@ const os = require('node:os');
 const path = require('node:path');
 const { execFile } = require('node:child_process');
 const { promisify } = require('node:util');
+const { processFailure } = require('../helpers/process-failure.cjs');
 const environment = fs.mkdtempSync(path.join(os.tmpdir(), 'ql-token-env-'));
 fs.writeFileSync(path.join(environment, '.env'), '');
 fs.mkdirSync(path.join(environment, 'data/db'), { recursive: true });
@@ -622,11 +623,7 @@ test('real SQLite and authentication cache retain concurrent process updates', a
     assert.equal(
       outcome.status,
       'fulfilled',
-      JSON.stringify({
-        code: outcome.reason?.code,
-        signal: outcome.reason?.signal,
-        killed: outcome.reason?.killed,
-      }),
+      JSON.stringify(processFailure(outcome.reason)),
     );
     return outcome.value;
   });
diff --git a/test/helpers/process-failure.cjs b/test/helpers/process-failure.cjs
new file mode 100644
index 00000000..47356444
--- /dev/null
+++ b/test/helpers/process-failure.cjs
@@ -0,0 +1,28 @@
+// execFile errors contain the command (including credentials), stdout and
+// stderr. Keep CI diagnostics useful without publishing any of those values.
+function processFailure(error, runtime = process) {
+  const stderr = String(error?.stderr || '');
+  return {
+    code: Number.isInteger(error?.code) ? error.code : null,
+    signal: /^SIG[A-Z0-9]+$/.test(error?.signal || '') ? error.signal : null,
+    killed: error?.killed === true,
+    node: runtime.versions.node,
+    arch: runtime.arch,
+    fatal: {
+      threadCreation:
+        /uv_thread_create|pthread_create|Failed to start thread|failed to create[^\n]*thread/i.test(
+          stderr,
+        ),
+      outOfMemory: /heap out of memory|Allocation failed|OutOfMemory/i.test(
+        stderr,
+      ),
+      v8Check: /Check failed:|Fatal error in/i.test(stderr),
+      heapBroker: /JSHeapBroker|compiler\/heap-refs/.test(stderr),
+      compiler: /v8::internal::(?:compiler|maglev)|PersistentHandles/.test(
+        stderr,
+      ),
+    },
+  };
+}
+
+module.exports = { processFailure };