Recognize crash mid OAuth2 token fetch as a network error

Windows security software that intercepts TLS (corporate antivirus,
proxies) can make mailsync's HTTPS client throw an uncaught C++
exception while fetching an OAuth2 access token, crashing the process
with SEH code 0xE06D7363 (the MSVC runtime's "C++ exception" signature)
before it can log the usual {"offline":true} marker. This bypassed the
existing network-failure detection in _buildCrashError, so every
occurrence surfaced to users as an unhelpful "unknown error" message
and was reported to Sentry as an unactionable crash (MAILSPRING-CLIENT-DH,
~100 Windows users hitting this exact exit code while linking a new
Gmail/Outlook account).

Detect this specific crash fingerprint - the known SEH code plus a log
tail showing the process died fetching an OAuth2 token - and classify
it the same as the existing offline-marker case.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01BfBhpanbqfLKX7csCsArzN

Author: claude

app/spec/mailsync-process-spec.ts

@@ -0,0 +1,43 @@
+import { MailsyncProcess } from '../src/mailsync-process';
+
+describe('MailsyncProcess._buildCrashError', () => {
+  let proc: MailsyncProcess;
+
+  beforeEach(() => {
+    proc = new MailsyncProcess({ configDirPath: '/tmp', resourcePath: '/tmp', verbose: false });
+  });
+
+  it('flags a crash with the offline marker during test mode as a network error', () => {
+    const rawLog = 'Testing connection\n{"offline":true,"retryable":true}\n';
+    const error: any = proc._buildCrashError('test', 1, null, rawLog);
+    expect(error.isNetworkError).toBe(true);
+    expect(error.message).not.toContain('unknown error');
+  });
+
+  it('flags a crash mid OAuth2 token fetch (SEH 0xE06D7363) during test mode as a network error', () => {
+    const rawLog =
+      'Waiting for Account JSON:\n\nWaiting for Identity JSON:\ninfo: Identity created at 123 - using ID Schema 1\ninfo: Fetching XOAuth2 access token (gmail) for abc123\n';
+    const error: any = proc._buildCrashError('test', 0xe06d7363, null, rawLog);
+    expect(error.isNetworkError).toBe(true);
+    expect(error.message).not.toContain('unknown error');
+  });
+
+  it('does not flag the same OAuth2 crash outside of test mode', () => {
+    const rawLog = 'info: Fetching XOAuth2 access token (gmail) for abc123\n';
+    const error: any = proc._buildCrashError('sync', 0xe06d7363, null, rawLog);
+    expect(error.isNetworkError).toBe(false);
+  });
+
+  it('does not flag an unrelated crash with the same exit code as a network error', () => {
+    const rawLog = 'Some other crash entirely, nothing about OAuth2\n';
+    const error: any = proc._buildCrashError('test', 0xe06d7363, null, rawLog);
+    expect(error.isNetworkError).toBe(false);
+    expect(error.message).toContain('unknown error');
+  });
+
+  it('reports a signal-terminated crash with the exit description in the message', () => {
+    const error: any = proc._buildCrashError('sync', null, 'SIGKILL' as NodeJS.Signals, 'crashed');
+    expect(error.isNetworkError).toBe(false);
+    expect(error.message).toContain('signal SIGKILL');
+  });
+});

app/src/mailsync-process.ts

@@ -325,13 +325,25 @@ export class MailsyncProcess extends EventEmitter {
   // requests and shouldn't have unrelated crashes reclassified this way - and
   // surface a friendly, localized, network-flagged error so callers can avoid
   // reporting it to Sentry.
+  //
+  // A second signature covers the same TLS-interception scenario when mailsync
+  // doesn't get a chance to log the offline marker at all: on Windows, security
+  // software that intercepts TLS (corporate antivirus, proxies, etc.) can make
+  // the HTTPS client throw an uncaught C++ exception mid-request, which crashes
+  // the process with SEH code 0xE06D7363 - the MSVC runtime's signature for an
+  // unhandled C++ exception - right after mailsync logs that it's about to fetch
+  // an OAuth2 access token (see MAILSPRING-CLIENT-DH, ~100 Windows users hitting
+  // this exact exit code while linking a new Gmail/Outlook account).
   _buildCrashError(
     mode: string,
     code: number | null,
     signal: NodeJS.Signals | null,
     rawLog: string
   ) {
-    const isNetworkFailure = mode === 'test' && /"offline"\s*:\s*true/.test(rawLog);
+    const hasOfflineMarker = /"offline"\s*:\s*true/.test(rawLog);
+    const crashedFetchingOAuthToken =
+      code === 0xe06d7363 && /Fetching XOAuth2 access token/.test(rawLog);
+    const isNetworkFailure = mode === 'test' && (hasOfflineMarker || crashedFetchingOAuthToken);
     const exitDescription = signal ? `signal ${signal}` : `${code}`;
     const error = isNetworkFailure
       ? new Error(LocalizedErrorStrings.ErrorConnection)