[31.x] Backport #35168 #36361

1. 
   fametrano commented at 9:35 PM on September 27, 2026: contributor

   Backports:

   • #35168

   v31.1 still has the pre-fix LoadBlockIndex. It re-adds a pruned block to m_blocks_unlinked when its parent is header-only (#35050). When the next block connects, CheckBlockIndex fails with Assertion failed: (!foundInUnlinked). -checkblockindex is on by default only on regtest, so this crashes functional-test suites run against 31.x. With default settings, nodes on mainnet, testnet and signet do not run this check, so they do not crash.

   Both commits are clean cherry-picks (-x). The only difference from master is context in test_runner.py. The new feature_prune_stale_fork.py fails on the v31.1 release binary with the assertion above. It passes on this branch, built from depends. Two runs each, on macOS arm64.

   Made with my usual tools: a computer, the Internet and an LLM. The mistakes, as usual, are all mine.

2. validation: Don't add pruned blocks to m_blocks_unlinked on startup

   LoadBlockIndex() adds to m_blocks_unlinked based only on nTx > 0, without
   checking BLOCK_HAVE_DATA. Pruning preserves nTx but clears BLOCK_HAVE_DATA,
   so a pruned block whose parent was header-only gets re-added on every
   restart, causing the CheckBlockIndex() assertion that entries must have
   data on disk to fail.
   
   Check that BLOCK_HAVE_DATA is set before inserting into m_blocks_unlinked.
   
   Fixes #35050.
   
   (cherry picked from commit 0e4b0bacecf94063342c7f9eb9b03dac8a7a7936)

   6cedc5d47e
3. test: Add coverage for m_blocks_unlinked invariant in LoadBlockIndex

   A pruned stale-fork block whose parent doesn't have any transactions
   shouldn't be added to m_blocks_unlinked when starting up a node.
   
   (cherry picked from commit 3f44f9aef7ccd0417fcd0c2f33f20615ea5c11e6)

   5ec487b9ae
4. DrahtBot added the label Backport on Sep 27, 2026
5. 
   DrahtBot commented at 9:35 PM on September 27, 2026: contributor

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   For details see: https://corecheck.dev/bitcoin/bitcoin/pulls/36361.

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6. fanquake added this to the milestone 31.2 on Oct 21, 2026

Milestone
31.2