Prune block_hashes at every checkpoint#6599
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A checkpoint only guarantees the availability of the blocks it vouches for in its `outbox_block_hashes`, so a node that bootstraps from it never learns the other pre-checkpoint blocks. Drop those from `block_hashes` when executing a checkpoint, so a node that has been following the chain all along converges on the same set. Retained below the checkpoint are the vouched-for blocks, which still carry unacknowledged messages, and any block still queued in an outbox: a queue is drained by a delivery confirmation from the recipient's validators, which is a separate path from the acknowledgement that empties `unfinalized_message_blocks`, so it can outlive the checkpoint's guarantee. For the vouched-for set to cover every `previous_message_blocks` anchor, the checkpoint also drops the anchor of each recipient that has acknowledged everything we sent it. Such an anchor would otherwise dangle even without any pruning, breaking a bootstrapped node on its next block to that recipient. Finally, `process_outgoing_messages` now treats a missing `block_hashes` entry for the outbox's previous height as "no predecessor" instead of a corrupted chain state -- the same state a bootstrapped node's rebuilt outbox is in.
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Motivation
A checkpoint only guarantees the availability of the blocks it vouches for in its
outbox_block_hashes, so a node that bootstraps from it never learns the other pre-checkpoint blocks.However, a node that just executes a block with a checkpoint, without bootstrapping from it, has its
block_hashescollection growing indefinitely.Proposal
Drop those from
block_hasheswhen executing a checkpoint. Retained below the checkpoint are the vouched-for blocks, which still carry unacknowledged messages, and any block still queued in an outbox.For the vouched-for set to cover every
previous_message_blocksanchor, the checkpoint also drops the anchor of each recipient that has acknowledged everything we sent it. Such an anchor would otherwise dangle even without any pruning, breaking a bootstrapped node on its next block to that recipient.Finally,
process_outgoing_messagesnow treats a missingblock_hashesentry for the outbox's previous height as "no predecessor" instead of a corrupted chain state -- the same state a bootstrapped node's rebuilt outbox is in.Test Plan
Tests were extended.
Release Plan
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