Fork detection script

Rename network type to chain type in detector.py

Author: ImplOfAnImpl

build-tools/fork-detection/README.md

@@ -0,0 +1,33 @@
+## Fork detection script, for the extra peace of mind
+
+Here we have `detector.py`, which is a relatively crude way of detecting a permanent fork (split)
+in the network if it happens.
+
+The script basically runs the full sync in a loop, checking the node's log output for certain errors
+and comparing its mainchain block ids with those obtained from the API server.\
+If anything suspicious is detected during the full sync, the script will save the node's data
+directory and log file.\
+In any case, the script will temporarily ban some of the peers that participated in the sync
+(so that the next iteration has a chance to have different ones and to reduce the strain on
+the network) and start the full sync all over again, reusing the peerdb from the previous iteration.
+
+The node is always run with checkpoints disabled, so that it has the chance to find older forks too.
+
+The structure of the script's working directory (specified via the command line):
+- `current_attempt` - this corresponds to the current sync attempt (iteration).
+- `saved_attempts` - this contains subdirectories corresponding to attempts that
+  are considered suspicious; each subdirectory's name is the datetime of the moment
+  when the attempt was finished.
+- `saved_peer_dbs` - this is where peer dbs from previous attempts are stored; the script
+  only needs the one from the latest attempt, but, just in case, the penultimate one is
+  also stored.
+- `log.txt` - this is the log of the script itself.
+
+Each attempt's directory has the following structure:
+- `flags` - this directory contains flag files (which are usually zero-length) indicating
+  that certain problems were found during the sync. It is what determines whether the attempt's
+  directory will be saved in the end (i.e. if the directory is non-empty, the attempt will be saved).
+- `node_data` - this is the node's data directory of this attempt.
+- `node_log.txt` - the node's log.
+
+Note: currently the script requires Python 3.13 to run, though we may lift this requirement later.