Recognize crash mid OAuth2 token fetch as a network error

[bengotow]

Fixes https://foundry-376-llc.sentry.io/issues/MAILSPRING-CLIENT-DH

What I observed

MAILSPRING-CLIENT-DH is "An unknown error has occurred mailsync: 3765269347" — 116 users impacted, 240 events, all on Windows. Every single sampled event (25/25) has the identical shape:

Waiting for Account JSON:

Waiting for Identity JSON:
info: Identity created at <ts> - using ID Schema 1
info: Fetching XOAuth2 access token (gmail) for <accountId>

...with mailsync exiting with code 3765269347, which is exactly 0xE06D7363 — the well-known Microsoft Visual C++ runtime SEH code that signals an uncaught C++ exception. This always happens in test mode, which is used by finalizeAndValidateAccount() (app/internal_packages/onboarding/lib/onboarding-helpers.ts) right after the user finishes the OAuth flow for a new Gmail/Outlook account.

So the pattern is: mailsync logs that it's about to fetch an OAuth2 access token, and then the process dies with a native C++ exception before it can log anything else — most likely because Windows security software that intercepts TLS (corporate antivirus, proxies, etc.) causes the HTTPS client to throw mid-request instead of failing gracefully.

MailsyncProcess._buildCrashError already has a heuristic for this exact class of problem (TLS interception during test mode), but it only fires when mailsync manages to log a {"offline":true} JSON marker before crashing. Here the crash happens too early for that marker to ever be written, so the heuristic never fires, and:

• Users see an unhelpful "unknown error ... 3765269347" message instead of "Connection Error - check your internet connection."
• oauth-signin-page.tsx's _onError only skips reporting to Sentry when err.isNetworkError (or isUserError) is set, so this crash — which isn't a fixable Mailspring bug — keeps flooding error tracking.

The actual native crash lives in the C++ sync engine (a separate repo), so it can't be root-caused or fixed from this codebase.

The fix

Widen _buildCrashError in app/src/mailsync-process.ts to also recognize this fingerprint: test mode, exit code 0xE06D7363, and a log tail showing the crash happened while fetching an OAuth2 token. When matched, it's classified the same way as the existing {"offline":true} case — the user gets the friendly, localized connection-error message, and the error is no longer reported to Sentry as an unexplained crash.

Added app/spec/mailsync-process-spec.ts covering both the existing offline-marker case and the new OAuth2-crash fingerprint (including that it's scoped to test mode and doesn't misclassify unrelated crashes that happen to share the same exit code).

Test plan

• Added unit tests for _buildCrashError covering both network-failure signatures and the negative cases (wrong mode, unrelated crash with the same exit code)
• Could not run the full Jasmine suite in this environment (no node_modules installed); verified the change compiles cleanly via an isolated tsc check

🤖 Generated with Claude Code

https://claude.ai/code/session_01BfBhpanbqfLKX7csCsArzN

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Generated by Claude Code

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PR Summary

Recognizes a specific Windows crash as a network error so affected users get a helpful message and the crash stops flooding Sentry. Sentry issue MAILSPRING-CLIENT-DH shows ~116 Windows users hitting exit code 3765269 (0xE06D7363, the MSVC signature for an uncaught C++ exception) right after mailsync logs it's about to fetch an OAuth2 token during new-account validation — most likely TLS-intercepting security software making the HTTPS client throw mid-request. The existing test-mode network-error heuristic only fired on an "offline":true log marker, which is never written when the crash happens this early.

• MailsyncProcess._buildCrashError now also flags isNetworkError when the exit code is 0xE06D7363 and the log contains Fetching XOAuth2 access token, additive to and preserving the existing offline-marker path, still scoped to mode === 'test'.
• As a result, oauth-signin-page._onError shows the localized connection-error message and skips reporting the crash to Sentry.
• Adds a mailsync-process-spec.ts unit spec covering the new signature plus guardrails: offline-marker case, mode scoping, matching exit code with an unrelated log, and signal-terminated crashes.

Issues

No issues found.

CI Checks

All CI checks passed on 6db1dd6.