🐛 Express error handler captures errors with an empty message and no request context #4241

What — server errors that reach the Express error handler with an empty message land in PostHog Error Tracking with nothing to read: no message, no stack, no route.
Why — such a group cannot be triaged: nobody can tell which request failed or whether a user saw it.

Scope

• Seen in a downstream consumer: one Error Tracking group with an empty message, no stack, level unset, source system — 5 events in 30 days, 2 in the last day, first seen 3 weeks ago.
• Level unset + source system match the 4-arg middleware in lib/services/errorTracker.js (setupExpressErrorHandler): it calls captureException(err, { distinctId, requestId }) only — no method, route or status. The Winston transport (logger.posthog.transport.js) always sets logLevel, so it is not the source.
• Fix: add method, the route path (no query string), and the status code to the captured properties; when err.message is empty, capture a message like <METHOD> <route> <status> so the group is named; skip expected 4xx (status < 500), as the logger does for expected outcomes.
• Tests: an error with an empty message passed to next() is captured with method, route and status; a 4xx is not captured.

Rank — P2: no user sees it, but the error is invisible to triage.

Filed by the gtm job
Created via /dev:issue