Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@minichain/chain.py`:
- Around line 123-126: The current verification uses temp_state after replaying
transactions only, but you must commit and verify the post-reward state
(including miner/reward) so all nodes reach the same state_root; update the
block acceptance path (the code using block.state_root, temp_state.state_root(),
and chain.state) to apply the miner reward to temp_state before computing and
comparing state_root, ensure the miner/reward fields are included in the hashed
block payload used to derive state_root, and only commit chain.state after
verifying that temp_state.state_root() (after reward) matches block.state_root.

In `@minichain/mpt.py`:
- Around line 8-10: The trie key conversion can crash on non-hex account keys;
add explicit hex-format validation and graceful errors: update to_nibbles to
first ensure key_hex is a str of hex characters (e.g., via a regex or
int(...,16) guard) and raise a clear ValueError mentioning the offending key,
and/or add a validation call from State.state_root before inserting keys to
confirm all keys are valid hex; also enforce hex checks at ingress points by
calling the existing is_valid_receiver (or similar) from _validate_sync_payload,
persistence.load/genesis allocation loading, and wherever accounts are inserted
so invalid addresses are rejected with a clear error instead of crashing in
to_nibbles.

In `@minichain/state.py`:
- Around line 16-27: state_root currently rebuilds a new Trie from self.accounts
on every call (using Trie(), trie.put(...), trie.root_hash()) which is O(N) per
invocation; change this to maintain the Trie incrementally by storing a
persistent trie instance (e.g., self._trie) and its cached root (e.g.,
self._cached_state_root) that are updated inside mutation points such as
apply_transaction and any methods that modify self.accounts (and
invalidated/updated in add_block when a rollback/alternative path occurs) so
state_root simply returns the cached root; ensure Trie.put/delete calls are
performed in apply_transaction (or a helper like _update_trie_for_account) and
that mutations clear or update the cached root to keep consistency.
- Around line 16-27: state_root() builds the committed MPT from self.accounts
including lazily-created empty accounts from State.get_account(), causing
divergent roots; update state_root (in class State) to skip inserting accounts
that are "empty" (e.g., default-created accounts with zero balance, zero nonce
and no storage) when iterating self.accounts before calling Trie.put, preserving
the sorted iteration and existing use of Trie.put/root_hash so only non-empty
accounts are committed to the trie.

---

Outside diff comments:
In `@minichain/p2p.py`:
- Around line 182-200: The validator currently allows omitting required keys
because it only checks that payload keys are a subset of allowed_fields and uses
payload.get(...) which returns None (accepted for state_root because its
expected type includes None); update _validate_message to explicitly verify all
required keys are present (e.g., assert set(required_fields).issubset(payload)
or loop to check membership before type checks) and change the expected type for
"state_root" in required_fields from (str, type(None)) to str so missing or None
values fail validation; keep the existing allowed_fields check but perform the
required-key presence check before the isinstance validations that iterate
required_fields.

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@minichain/mpt.py`:
- Around line 10-13: The current except block discards the original parse
exception which loses diagnostic details; update the handler around the list
comprehension that parses key_hex (the try/except that returns [int(c, 16) for c
in key_hex]) to capture the original ValueError (e.g., except ValueError as e)
and re-raise the new ValueError using exception chaining (raise
ValueError(f"Invalid MPT key: '{key_hex}'. Keys must be valid hex strings.")
from e) so the original parse failure is preserved for debugging.

---

Outside diff comments:
In `@main.py`:
- Around line 149-157: Received blocks are being credited twice: chain.add_block
already applies the miner reward and commits temp_state, so remove the redundant
post-acceptance credit. Delete or stop calling
chain.state.credit_mining_reward(miner) in the block-receive path (the block
acceptance branch where logger.info("📥 Received Block #%d — added to chain") is
logged) and leave mempool.remove_transactions(block.transactions) intact; ensure
you still derive miner with payload.get("miner", BURN_ADDRESS) only if needed
elsewhere (BURN_ADDRESS may become unused and can be cleaned up).