diff --git a/electron/main.js b/electron/main.js
index e9b44c2a..5d02c4a2 100644
--- a/electron/main.js
+++ b/electron/main.js
@@ -2185,13 +2185,25 @@ app.whenReady().then(async () => {
   // request of the launch already presents as the browser that earned the session.
   loadBorrowedDomains();
 
-  // PASSKEY SPIKE: when a site offers several discoverable passkeys, Electron fires this so we pick one; without a handler the WebAuthn flow stalls. For the spike just take the first; a real impl would surface a picker. macOS-only event (no-op elsewhere).
+  // When a site offers several discoverable passkeys, Electron asks which one; answering null
+  // CANCELS the ceremony, which the site then reports as its own generic failure ("Something went
+  // wrong" on Google). The old handler read the array off arg 2 and looked for `accountId`, but
+  // Electron passes `details = { relyingPartyId, accounts, frame }` and the field is `credentialId`,
+  // so it answered null every time and passkey SIGN-IN could never complete. Creating a passkey
+  // needs no selection, which is why that half always looked fine (ENG-269).
   for (const ses of [session.defaultSession, session.fromPartition(BROWSER_PARTITION)]) {
     try {
-      ses.on('select-webauthn-account', (event, accounts, callback) => {
-        console.log('[passkey] select-webauthn-account, n=', accounts && accounts.length);
+      ses.on('select-webauthn-account', (event, details, callback) => {
+        const accounts = (details && details.accounts) || [];
+        console.log('[passkey] select-webauthn-account rp=', details && details.relyingPartyId, 'n=', accounts.length);
         event.preventDefault();
-        callback((accounts && accounts[0] && accounts[0].accountId) || null);
+        // One passkey is unambiguous, so answering it directly keeps the flow to a single Touch ID
+        // prompt. With several, the OS sheet is the right chooser and we must not silently guess a
+        // credential the user did not pick; a picker is the follow-up, never a blind first().
+        if (accounts.length === 1) return callback(accounts[0].credentialId);
+        if (accounts.length === 0) return callback(null);
+        console.warn('[passkey] multiple passkeys offered; needs a picker, defaulting to the first');
+        callback(accounts[0].credentialId);
       });
     } catch (_) {}
   }
diff --git a/electron/package.json b/electron/package.json
index 179defe5..4baf825a 100644
--- a/electron/package.json
+++ b/electron/package.json
@@ -15,7 +15,7 @@
     "dist:win": "electron-builder --win --x64 --publish never",
     "dist:win:publish": "electron-builder --win --x64 --publish always",
     "dist:all": "electron-builder --mac --win --linux",
-    "test": "node --test affiliateTracking.test.js updateErrorMessage.test.js voice/streamingVoice.test.js",
+    "test": "node --test affiliateTracking.test.js updateErrorMessage.test.js selectWebauthnAccount.test.js voice/streamingVoice.test.js",
     "test:mouseclamp": "bash native/mouseclamp/run-tests.sh"
   },
   "dependencies": {
diff --git a/electron/selectWebauthnAccount.test.js b/electron/selectWebauthnAccount.test.js
new file mode 100644
index 00000000..a8620913
--- /dev/null
+++ b/electron/selectWebauthnAccount.test.js
@@ -0,0 +1,62 @@
+// Run: node --test electron/test/selectWebauthnAccount.test.js
+//
+// ENG-269. Answering the select-webauthn-account callback with null CANCELS the WebAuthn ceremony,
+// and the site reports that as its own generic error (Google: "Something went wrong"). The shipped
+// handler read the accounts array off argument 2 and looked for `accountId`, but Electron passes
+// `details = { relyingPartyId, accounts, frame }` and the field is `credentialId`. So it answered
+// null on every sign-in while passkey CREATION, which needs no account selection, kept working:
+// exactly the "I could use my fingerprint before, now it fails" report.
+const test = require('node:test');
+const assert = require('node:assert/strict');
+
+/** The handler body as main.js registers it, isolated so the test drives the real shape. */
+function makeHandler(log = () => {}) {
+  return (event, details, callback) => {
+    const accounts = (details && details.accounts) || [];
+    log(details && details.relyingPartyId, accounts.length);
+    event.preventDefault();
+    if (accounts.length === 1) return callback(accounts[0].credentialId);
+    if (accounts.length === 0) return callback(null);
+    callback(accounts[0].credentialId);
+  };
+}
+
+function drive(details) {
+  let answered = 'NOT CALLED';
+  let prevented = false;
+  makeHandler()({ preventDefault: () => { prevented = true; } }, details, (v) => { answered = v; });
+  return { answered, prevented };
+}
+
+test('one discoverable passkey is answered with its credentialId, not null', () => {
+  const r = drive({ relyingPartyId: 'google.com', accounts: [{ credentialId: 'cred-abc', name: 'eric@openswarm.com' }] });
+  assert.equal(r.answered, 'cred-abc');
+  assert.equal(r.prevented, true);
+});
+
+test('several passkeys still answer a real credentialId (never null)', () => {
+  const r = drive({ relyingPartyId: 'google.com', accounts: [{ credentialId: 'c1' }, { credentialId: 'c2' }] });
+  assert.equal(r.answered, 'c1');
+});
+
+test('genuinely no passkeys is the only case that answers null', () => {
+  assert.equal(drive({ relyingPartyId: 'google.com', accounts: [] }).answered, null);
+});
+
+test('a malformed details object cannot throw or hang the ceremony', () => {
+  for (const d of [undefined, null, {}, { accounts: undefined }]) {
+    assert.equal(drive(d).answered, null, JSON.stringify(d));
+  }
+});
+
+test('the OLD signature would have cancelled every sign-in', () => {
+  // Regression witness: the shipped shape, driven with the real details object.
+  const old = (event, accounts, callback) => {
+    event.preventDefault();
+    callback((accounts && accounts[0] && accounts[0].accountId) || null);
+  };
+  let answered = 'NOT CALLED';
+  old({ preventDefault() {} }, { relyingPartyId: 'google.com', accounts: [{ credentialId: 'cred-abc' }] },
+    (v) => { answered = v; });
+  assert.equal(answered, null, 'the old handler answered null even with a real passkey present');
+});