[BUG]: the entire chain lived in memory and was lost on every restart

[aniket866]

Bug Description

What

Adds minichain/persistence.py — a minimal module that can write the full blockchain and account state to disk and restore it across sessions.

data/
  blockchain.json   ← serialized list of blocks
  state.json        ← accounts dict (balances, nonces, contract storage)

Why

Previously the entire chain lived in memory and was lost on every restart. This made multi-session research, demos, and testnet usage impossible.

API

from minichain.persistence import save, load
Save
save(blockchain, path="data/")
Restore
blockchain = load(path="data/")

load() returns a fully working Blockchain instance — new blocks can be mined and added immediately after loading.

Steps to Reproduce

No response

Logs and Screenshots

No response

Environment Details

No response

Impact

Critical - Application is unusable

Code of Conduct

• I have joined the Discord server and will post updates there
• I have searched existing issues to avoid duplicates