its not possible to start a node when no proposer

[srene]

even if proposer is sentinel it may be necessary to start a node as full-node. rn it does not allow to start a node after sequencer is rotated to sentinel.

[danwt]

This is just an operator friendliness issue? Or something more critical?

[mtsitrin]

I see it as 2 subfeatures:
For halted rollapp:

1. Operator should be able to sync to the last height
2. Operator's node should be up and running waiting for the fork event to happen once sequencer registered

1 is mandatory, 2 is nice to have

[mtsitrin]

related to #1040