fix(feature-flags): Keep polling when no error listener is attached

[stanleyphu]

Why

A runtime client with no error listener crashes the host process on its first failed poll. poll() runs from a timer, and emitting error with nothing listening throws, because the emitter follows Node's EventEmitter. The throw escapes as an unhandled rejection and skips the retry. On a 401 it also skips failed and the waitUntilReady() rejection, so callers' try/catch around waitUntilReady() never runs. #1630 called this out as a pre-existing follow-up. Every example in the runtime client docs except the events one creates a client without an error listener, and so does getFeatureFlagsRuntimeClient() in authkit-nextjs.

• The poll loop emits error only when a listener is attached. With no listener and no logger, it warns once through workos.emitWarning and keeps retrying, so failures still aren't silent. A 401 always gets its own warning that syncing stopped, even after an earlier failure warned.
• 401 handling is unchanged: failed fires, polling stops, and waitUntilReady() rejects with UnauthorizedException before initialization.
• Calling client.emit('error') directly with no listener still throws.

Merging this before the release PR (#1722) ships it in 12.0.0.

Not covered by CI

• Ran the runtime client guide's main example, unchanged (no error listener, try/catch around waitUntilReady()), against builds of main and this branch, with scripted API responses.
• The four new tests fail on main: polling stops after an unobserved failure, waitUntilReady() never rejects on a 401, and nothing warns. They pass here.

Proof

main, 401 on the first poll:
  UnauthorizedException thrown from the poll timer; the process exits and the example's catch never runs

this branch, 401 on the first poll:
  Runtime client failed to initialize: UnauthorizedException: Could not authorize the request. Maybe your API key is invalid?

main, one poll fails all four attempts:
  the process exits with an unhandled rejection

this branch, same:
  (node) WorkOS: Feature flag sync failed and no 'error' listener or logger is attached; keeping the last good flags and retrying. ...
  later polls return 200, and the process is still running 2 seconds later

🤖 Generated with Claude Code

[stanleyphu]

@greptileai review this draft

[greptile-apps]

Confidence Score: 5/5

[Medium impact] The PR appears safe to merge, with no outstanding findings.

Summary

Keeps background polling alive when no error listener is attached.

• Flag polling reports unobserved errors and preserves retries and 401 stops.

The previous unnumbered finding is fixed: the 401 warning now says syncing stopped rather than promising retries.

_{Reviews (2) · Last reviewed commit: "fix(feature-flags): Warn when a 401 stop..." · Reviewed by Greptile}

[stanleyphu]

@greptileai review