## What changed?
Tweak the "return special error if no recent poller when we're near the
deadline" logic:
- Use a one-shot timer instead of a context.
- Move it into the loop so that it also can activate in the
errForwarderSlowDown case.
## Why?
- Context Done channels are closed, so it becomes a busy loop after
close. A timer is more efficient here anyway.
- Use the logic in more potential situations for better error messages.
## How did you test it?
Existing tests. The previous code had correct behavior besides the busy
loop.
