GetBlockIDAtHeight said "not implemented" on I, Z and B while returning a real
answer on K, F, Q, G, S and M. The store writes the height entry in the same
commit as the block, so on these three it was a stub in front of an index that
already existed — and the engine resolves blocks by height when it bootstraps
and when it state-syncs.
Each is now one line onto that index, which cannot name a block the chain did
not accept because the two are the same commit. A test on each proves it: a
block whose commit is refused has no height entry, and gets one when it lands.
zeekay
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