Diagnostics should capture fatal server failures without replacing the terminal stderr signal that developers rely on during local startup. Fatal uncaught exceptions now print their stack to stderr, persist the diagnostic event, and exit non-zero so repeated server starts expose port conflicts immediately.
Constraint: Startup diagnostics must still write sanitized runtime events for export bundles.
Rejected: Only document checking runtime-errors.log | developers should not lose the standard stderr failure path.
Confidence: high
Scope-risk: narrow
Directive: Do not install process-level exception handlers that swallow fatal startup errors without preserving stderr and non-zero exit behavior.
Tested: bun test src/server/__tests__/diagnostics-service.test.ts
Tested: bun run check:server
Tested: SERVER_PORT=3456 bun run src/server/index.ts returned exit=1 and printed the port-conflict stack while diagnostics recorded the event
8b07c16f45