validation: insert assumed-valid block index entries into candidates

src/validation.cpp

@@ -3773,7 +3773,9 @@ bool BlockManager::LoadBlockIndex(
             pindex->nStatus |= BLOCK_FAILED_CHILD;
             setDirtyBlockIndex.insert(pindex);
         }
-        if (pindex->IsValid(BLOCK_VALID_TRANSACTIONS) && (pindex->HaveTxsDownloaded() || pindex->pprev == nullptr)) {
+        if (pindex->IsAssumedValid() ||
+                (pindex->IsValid(BLOCK_VALID_TRANSACTIONS) &&
+                 (pindex->HaveTxsDownloaded() || pindex->pprev == nullptr))) {
             block_index_candidates.insert(pindex);
         }
         if (pindex->nStatus & BLOCK_FAILED_MASK && (!pindexBestInvalid || pindex->nChainWork > pindexBestInvalid->nChainWork))

src/validation.h

@@ -647,9 +647,10 @@ public:
     const std::optional<uint256> m_from_snapshot_blockhash;
 
     /**
-     * The set of all CBlockIndex entries with BLOCK_VALID_TRANSACTIONS (for itself and all ancestors) and
+     * The set of all CBlockIndex entries with either BLOCK_VALID_TRANSACTIONS (for
-     * as good as our current tip or better. Entries may be failed, though, and pruning nodes may be
+     * itself and all ancestors) *or* BLOCK_ASSUMED_VALID (if using background
-     * missing the data for the block.
+     * chainstates) and as good as our current tip or better. Entries may be failed,
+     * though, and pruning nodes may be missing the data for the block.
      */
     std::set<CBlockIndex*, CBlockIndexWorkComparator> setBlockIndexCandidates;