validation: do not add the snapshot to candidates set of the background chainstate #34786

1. 
   mzumsande commented at 11:53 am on March 10, 2026: contributor

   The snapshot block needs to be added to the candidates set of the assumed-valid chain because it will be the tip of that chainstate right after snapshot activation.

   However, adding it also to the background chainstate is not necessary for anything. Before, the index would be in the set without being connectable. It will be eventually added to the set as part of the normal block download - no extra logic is necessary here.

   This simplifies a unit test which had a comment that having the block in the set is “not intended”. This was suggested here and here in #34521

   Note that adding the snapshot block was harmless, since FindMostWorkChain() lazily removes blocks without data from the set, so this does not fix a bug but just simplifies some code.

2. validation: do not add the snapshot block to candidates of bg chainstate

   The snapshot block needs to be added to the candidates set of the
   assumed-valid chain because it will be the tip of that chainstate
   right after snapshot activation.
   However, adding it also to the background chainstate is not necessary
   for anything. Before, the index would linger in the set without being
   connectable. It will be eventually added to the set as part of the
   normal block download - no extra logic is necessary here.

   69baddc910
3. DrahtBot added the label Validation on Mar 10, 2026
4. 
   DrahtBot commented at 11:54 am on March 10, 2026: contributor

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5. 
   sedited commented at 4:55 pm on March 10, 2026: contributor

   Concept ACK, thanks for the follow up.

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