feat(backfill): --resume a halted run from the store's last checkpoint - #4
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A long replay that halted (bad block, vote mismatch, crash) had to start over from the snapshot. Now the disk store periodically commits a checkpoint and --resume picks up from it, no snapshot needed. A checkpoint is the buffered accounts plus the bank-hash roll state (2048 LE lattice bytes ++ the 32-byte hash, same layout as the snapshot trailer) written in one durable redb commit, so a crash can't land the accounts without the checkpoint that describes them. What makes it sound is checkpoint_mode: once seeding is done, put() stops auto-flushing and flush() no-ops, leaving checkpoint_flush as the only committer. The redb therefore never holds writes past the last checkpoint, so resuming from it can't replay onto state that already moved. The checkpoint is written even when a chunk buffered nothing, so a no-write chunk still advances the slot.
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A long replay that halted (bad block, vote mismatch, crash) had to start over from the snapshot. Now the disk store periodically commits a checkpoint and --resume picks up from it, no snapshot needed.
A checkpoint is the buffered accounts plus the bank-hash roll state (2048 LE lattice bytes ++ the 32-byte hash, same layout as the snapshot trailer) written in one durable redb commit, so a crash can't land the accounts without the checkpoint that describes them.
What makes it sound is checkpoint_mode: once seeding is done, put() stops auto-flushing and flush() no-ops, leaving checkpoint_flush as the only committer. The redb therefore never holds writes past the last checkpoint, so resuming from it can't replay onto state that already moved. The checkpoint is written even when a chunk buffered nothing, so a no-write chunk still advances the slot.