I am presently implementing the rpc name invalidateblock on btcd, an alternate Bitcoin full node implementation. I am attempting to determine how Bitcoin Core handles department choice on reorganizations with invalidateblock.

Say there’s 3 chaintips like so:

genesis -> 1  -> 2  -> 3  (energetic)     (chainwork=8)
       -> 1a             (valid-fork) (chainwork=4)
       -> 1b             (valid-fork) (chainwork=6)

Blocks at peak 1 had been acquired within the order of: 1, 1a, 1b. Block 1 was acquired most lately and block 1b was acquired final.

If I name invalidateblock on block 2, which block will change into the energetic chaintip?