Properly define the core pallet instead of placing it within the runtime

substrate/core/Cargo.toml

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+[package]
+name = "serai-core-pallet"
+version = "0.1.0"
+description = "Core pallet"
+license = "AGPL-3.0-only"
+repository = "https://github.com/serai-dex/serai/tree/develop/substrate/core"
+authors = ["Luke Parker <lukeparker5132@gmail.com>"]
+edition = "2021"
+rust-version = "1.85"
+
+[package.metadata.docs.rs]
+all-features = true
+rustdoc-args = ["--cfg", "docsrs"]
+
+[package.metadata.cargo-machete]
+ignored = ["scale"]
+
+[lints]
+workspace = true
+
+[dependencies]
+borsh = { version = "1", default-features = false, features = ["derive", "de_strict_order"] }
+
+scale = { package = "parity-scale-codec", version = "3", default-features = false, features = ["derive"] }
+
+sp-core = { git = "https://github.com/serai-dex/patch-polkadot-sdk", rev = "d4624c561765c13b38eb566e435131a8c329a543", default-features = false }
+sp-io = { git = "https://github.com/serai-dex/patch-polkadot-sdk", rev = "d4624c561765c13b38eb566e435131a8c329a543", default-features = false }
+
+frame-system = { git = "https://github.com/serai-dex/patch-polkadot-sdk", rev = "d4624c561765c13b38eb566e435131a8c329a543", default-features = false }
+frame-support = { git = "https://github.com/serai-dex/patch-polkadot-sdk", rev = "d4624c561765c13b38eb566e435131a8c329a543", default-features = false }
+
+serai-abi = { path = "../abi", default-features = false, features = ["substrate"] }
+
+[features]
+std = [
+  "borsh/std",
+  "scale/std",
+
+  "sp-core/std",
+  "sp-io/std",
+
+  "frame-system/std",
+  "frame-support/std",
+
+  "serai-abi/std",
+]
+
+runtime-benchmarks = [
+  "frame-system/runtime-benchmarks",
+  "frame-support/runtime-benchmarks",
+]
+
+# TODO
+try-runtime = []
+
+default = ["std"]

substrate/core/LICENSE

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+AGPL-3.0-only license
+
+Copyright (c) 2023-2025 Luke Parker
+
+This program is free software: you can redistribute it and/or modify
+it under the terms of the GNU Affero General Public License Version 3 as
+published by the Free Software Foundation.
+
+This program is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+GNU Affero General Public License for more details.
+
+You should have received a copy of the GNU Affero General Public License
+along with this program. If not, see <http://www.gnu.org/licenses/>.

substrate/core/README.md

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+# Serai Core Pallet

substrate/core/src/iumt.rs

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+use core::marker::PhantomData;
+
+use borsh::BorshSerialize;
+
+use serai_abi::primitives::merkle::{UnbalancedMerkleTree, IncrementalUnbalancedMerkleTree as Iumt};
+
+/// A wrapper around a `StorageValue` which offers a high-level API as an
+/// `IncrementalUnbalancedMerkleTree`.
+pub struct IncrementalUnbalancedMerkleTree<
+  T: frame_support::StorageValue<Iumt, Query = Option<Iumt>>,
+  const BRANCH_TAG: u8 = 1,
+  const LEAF_TAG: u8 = 0,
+>(PhantomData<T>);
+impl<
+    T: frame_support::StorageValue<Iumt, Query = Option<Iumt>>,
+    const BRANCH_TAG: u8,
+    const LEAF_TAG: u8,
+  > IncrementalUnbalancedMerkleTree<T, BRANCH_TAG, LEAF_TAG>
+{
+  /// Create a new Merkle tree, expecting there to be none already present.
+  ///
+  /// Panics if a Merkle tree was already present.
+  pub fn new_expecting_none() {
+    T::mutate(|value| {
+      assert!(value.is_none());
+      *value = Some(Iumt::new());
+    });
+  }
+  /// Append a leaf to the Merkle tree.
+  ///
+  /// Panics if no Merkle tree was present.
+  pub fn append<L: BorshSerialize>(leaf: &L) {
+    let leaf = sp_core::blake2_256(&borsh::to_vec(&(LEAF_TAG, leaf)).unwrap());
+
+    T::mutate(|value| {
+      let tree = value.as_mut().unwrap();
+      tree.append(BRANCH_TAG, leaf);
+    })
+  }
+  /// Get the unbalanced merkle tree.
+  ///
+  /// Panics if no Merkle tree was present.
+  pub fn get() -> UnbalancedMerkleTree {
+    T::get().unwrap().calculate(BRANCH_TAG)
+  }
+  /// Take the Merkle tree.
+  ///
+  /// Panics if no Merkle tree was present.
+  pub fn take() -> UnbalancedMerkleTree {
+    T::mutate(|value| value.take().unwrap().calculate(BRANCH_TAG))
+  }
+}

substrate/core/src/lib.rs

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+#![cfg_attr(docsrs, feature(doc_auto_cfg))]
+#![doc = include_str!("../README.md")]
+#![deny(missing_docs)]
+#![cfg_attr(not(feature = "std"), no_std)]
+
+use core::marker::PhantomData;
+
+use frame_support::pallet_prelude::*;
+
+use serai_abi::{
+  primitives::{prelude::*, merkle::IncrementalUnbalancedMerkleTree as Iumt},
+  *,
+};
+
+mod iumt;
+pub use iumt::*;
+
+#[frame_support::pallet]
+mod pallet {
+  use super::*;
+
+  /// The set of all blocks prior added to the blockchain.
+  #[pallet::storage]
+  pub(super) type Blocks<T: Config> = StorageMap<_, Identity, T::Hash, (), OptionQuery>;
+  /// The Merkle tree of all blocks added to the blockchain.
+  #[pallet::storage]
+  #[pallet::unbounded]
+  pub(super) type BlocksCommitment<T: Config> = StorageValue<_, Iumt, OptionQuery>;
+  pub(super) type BlocksCommitmentMerkle<T> = IncrementalUnbalancedMerkleTree<BlocksCommitment<T>>;
+
+  /// The Merkle tree of all transactions within the current block.
+  #[pallet::storage]
+  #[pallet::unbounded]
+  pub(super) type BlockTransactionsCommitment<T: Config> = StorageValue<_, Iumt, OptionQuery>;
+  pub(super) type BlockTransactionsCommitmentMerkle<T> =
+    IncrementalUnbalancedMerkleTree<BlockTransactionsCommitment<T>>;
+
+  /// The hashes of events caused by the current transaction.
+  #[pallet::storage]
+  #[pallet::unbounded]
+  pub(super) type TransactionEvents<T: Config> = StorageValue<_, Iumt, OptionQuery>;
+  pub(super) type TransactionEventsMerkle<T> = IncrementalUnbalancedMerkleTree<
+    TransactionEvents<T>,
+    TRANSACTION_EVENTS_COMMITMENT_BRANCH_TAG,
+    TRANSACTION_EVENTS_COMMITMENT_LEAF_TAG,
+  >;
+  /// The roots of the Merkle trees of each transaction's events.
+  #[pallet::storage]
+  #[pallet::unbounded]
+  pub(super) type BlockEventsCommitment<T: Config> = StorageValue<_, Iumt, OptionQuery>;
+  pub(super) type BlockEventsCommitmentMerkle<T> = IncrementalUnbalancedMerkleTree<
+    BlockEventsCommitment<T>,
+    EVENTS_COMMITMENT_BRANCH_TAG,
+    EVENTS_COMMITMENT_LEAF_TAG,
+  >;
+
+  /// A mapping from an account to its next nonce.
+  #[pallet::storage]
+  type NextNonce<T: Config> = StorageMap<_, Blake2_128Concat, SeraiAddress, T::Nonce, ValueQuery>;
+
+  #[pallet::config]
+  pub trait Config: frame_system::Config<Hash: Into<[u8; 32]>> {}
+
+  #[pallet::pallet]
+  pub struct Pallet<T>(_);
+
+  impl<T: Config> Pallet<T> {
+    /// If a block exists on the current blockchain.
+    #[must_use]
+    pub fn block_exists(hash: impl scale::EncodeLike<T::Hash>) -> bool {
+      Blocks::<T>::contains_key(hash)
+    }
+
+    /// The next nonce for an account.
+    #[must_use]
+    pub fn next_nonce(account: &SeraiAddress) -> T::Nonce {
+      NextNonce::<T>::get(account)
+    }
+
+    /// Consume the next nonce for an account.
+    ///
+    /// Panics if the current nonce is `<_>::MAX`.
+    pub fn consume_next_nonce(signer: &SeraiAddress) {
+      NextNonce::<T>::mutate(signer, |value| {
+        *value = value
+          .checked_add(&T::Nonce::one())
+          .expect("`consume_next_nonce` called when current nonce is <_>::MAX")
+      });
+    }
+
+    /// The code to run when beginning execution of a transaction.
+    ///
+    /// The caller MUST ensure two transactions aren't simultaneously started.
+    pub fn start_transaction() {
+      TransactionEventsMerkle::<T>::new_expecting_none();
+    }
+    /// Emit an event.
+    // TODO: Have this called
+    pub fn emit_event(event: impl TryInto<serai_abi::Event>) {
+      if let Ok(event) = event.try_into() {
+        TransactionEventsMerkle::<T>::append(&event);
+      }
+    }
+    /// End execution of a transaction.
+    pub fn end_transaction(transaction_hash: [u8; 32]) {
+      BlockTransactionsCommitmentMerkle::<T>::append(&transaction_hash);
+
+      let transaction_events_root = TransactionEventsMerkle::<T>::take().root;
+
+      // Append the leaf (the transaction's hash and its events' root) to the block's events'
+      // commitment
+      BlockEventsCommitmentMerkle::<T>::append(&(&transaction_hash, &transaction_events_root));
+    }
+  }
+}
+pub use pallet::*;
+
+/// The code to run at the start of a block for this pallet.
+pub struct StartOfBlock<T: Config>(PhantomData<T>);
+impl<T: Config> frame_support::traits::PreInherents for StartOfBlock<T> {
+  fn pre_inherents() {
+    if frame_system::Pallet::<T>::block_number().is_zero() {
+      BlocksCommitmentMerkle::<T>::new_expecting_none();
+    } else {
+      let parent_hash = frame_system::Pallet::<T>::parent_hash();
+      Blocks::<T>::set(parent_hash, Some(()));
+      let parent_hash: [u8; 32] = parent_hash.into();
+      BlocksCommitmentMerkle::<T>::append(&parent_hash);
+    }
+
+    BlockTransactionsCommitmentMerkle::<T>::new_expecting_none();
+    BlockEventsCommitmentMerkle::<T>::new_expecting_none();
+  }
+}
+
+/// The code to run at the end of a block for this pallet.
+pub struct EndOfBlock<T: Config>(PhantomData<T>);
+impl<T: Config> frame_support::traits::PostTransactions for EndOfBlock<T> {
+  fn post_transactions() {
+    frame_system::Pallet::<T>::deposit_log(
+      frame_support::sp_runtime::generic::DigestItem::Consensus(
+        SeraiExecutionDigest::CONSENSUS_ID,
+        borsh::to_vec(&SeraiExecutionDigest {
+          builds_upon: BlocksCommitmentMerkle::<T>::get(),
+          transactions_commitment: BlockTransactionsCommitmentMerkle::<T>::take(),
+          events_commitment: BlockEventsCommitmentMerkle::<T>::take(),
+        })
+        .unwrap(),
+      ),
+    );
+  }
+}