Unpopular opinion; a full node enforcing Segwit is more likely to find itself on an fork than an SPV client ... I know this is insane to say, but it is true, If enough economic nodes decided to run older bitcoin core versions, miners can safely mine an invalid block according to segwit, and the full node will reject it, but the SPV will just follow the heaviest chain which after 6 blocks is very likely representing the economic majority, and definitely after 100 blocks, or 2016 or whatever threshold that makes you feel safe.
At the very least, full nodes should halt receiving funds if they see sudden drop of difficulty or significant block time lag... But... That is also what SPV clients should do.
Literally all boils down to; heaviest chain is the only objective proxy for consensus and if that doesn't work you HAVE to manually intervene and make a judgement call.
At the very least, full nodes should halt receiving funds if they see sudden drop of difficulty or significant block time lag... But... That is also what SPV clients should do.
Literally all boils down to; heaviest chain is the only objective proxy for consensus and if that doesn't work you HAVE to manually intervene and make a judgement call.