This PR allows users to prune their nodes up to the Prague fork. It
indirectly depends on #32157 and can't really be merged before eraE
files are widely available for download.
The `--history.chain` flag becomes mandatory for `prune-history`
command. Here I've listed all the edge cases that can happen and how we
behave:
## prune-history Behavior
| From | To | Result |
|-------------|--------------|--------------------------|
| full | postmerge | ✅ prunes |
| full | postprague | ✅ prunes |
| postmerge | postprague | ✅ prunes further |
| postprague | postmerge | ❌ can't unprune |
| any | all | ❌ use import-history |
## Node Startup Behavior
| DB State | Flag | Result |
|-------------|--------------|----------------------------------------------------------------|
| fresh | postprague | ✅ syncs from Prague |
| full | postprague | ❌ "run prune-history first" |
| postmerge | postprague | ❌ "run prune-history first" |
| postprague | postmerge | ❌ "can't unprune, use import-history or fix
flag" |
| pruned | all | ✅ accepts known prune points |
I added the history mode configuration in eth/ethconfig initially, since
it seemed like the logical place. But it turns out we need access to the
intended pruning setting at a deeper level, and it actually needs to be
integrated with the blockchain startup procedure.
With this change applied, if a node previously had its history pruned,
and is subsequently restarted **without** the `--history.chain
postmerge` flag, the `BlockChain` initialization code will now verify
the freezer tail against the known pruning point of the predefined
network and will restore pruning status. Note that this logic is quite
restrictive, we allow non-zero tail only for known networks, and only
for the specific pruning point that is defined.
