pop-fork 0.13.0

// SPDX-License-Identifier: GPL-3.0

//! Blockchain manager for forked chains.
//!
//! This module provides the [`Blockchain`] struct, which is the main entry point
//! for creating and interacting with local forks of live Polkadot SDK chains.
//!
//! # Architecture
//!
//! ```text
//! ┌─────────────────────────────────────────────────────────────────┐
//! │                        Blockchain                               │
//! │                                                                 │
//! │   fork() ──────► Connect to live chain                          │
//! │                        │                                        │
//! │                        ▼                                        │
//! │              Create fork point Block                            │
//! │                        │                                        │
//! │                        ▼                                        │
//! │              Initialize RuntimeExecutor                         │
//! │                        │                                        │
//! │                        ▼                                        │
//! │              Detect chain type (relay/para)                     │
//! │                        │                                        │
//! │                        ▼                                        │
//! │              Ready for block building                           │
//! └─────────────────────────────────────────────────────────────────┘
//! ```
//!
//! # Example
//!
//! ```ignore
//! use pop_fork::Blockchain;
//! use url::Url;
//!
//! // Fork a live chain
//! let endpoint: Url = "wss://rpc.polkadot.io".parse()?;
//! let blockchain = Blockchain::fork(&endpoint, None).await?;
//!
//! // Get chain info
//! println!("Chain: {}", blockchain.chain_name());
//! println!("Fork point: {:?}", blockchain.fork_point());
//!
//! // Build a block with extrinsics
//! let block = blockchain.build_block(vec![extrinsic]).await?;
//!
//! // Query storage at head
//! let value = blockchain.storage(&key).await?;
//! ```

use crate::{
	Block, BlockBuilder, BlockBuilderError, BlockError, BlockForkPoint, CacheError, ExecutorConfig,
	ExecutorError, ForkRpcClient, InherentProvider, RuntimeExecutor, StorageCache,
	builder::ApplyExtrinsicResult,
	create_next_header_with_slot, default_providers,
	strings::{
		inherent::{parachain::storage_keys, timestamp::slot_duration},
		txpool::{runtime_api, transaction_source},
	},
};
use scale::Decode;
use std::{
	path::Path,
	sync::{
		Arc,
		atomic::{AtomicU64, Ordering},
	},
};
use subxt::config::substrate::H256;
use tokio::sync::{OnceCell, RwLock, broadcast};
use url::Url;

/// Minimum interval (in seconds) between reconnection log messages at DEBUG level.
/// More frequent reconnections are logged at TRACE to reduce noise.
const RECONNECT_LOG_DEBOUNCE_SECS: u64 = 30;

pub type BlockBody = Vec<Vec<u8>>;

// Transaction validity types for decoding TaggedTransactionQueue_validate_transaction results.

/// Result of transaction validation.
///
/// Mirrors `sp_runtime::transaction_validity::TransactionValidity`.
#[derive(Debug, Clone, Decode)]
pub enum TransactionValidity {
	/// Transaction is valid.
	#[codec(index = 0)]
	Ok(ValidTransaction),
	/// Transaction is invalid.
	#[codec(index = 1)]
	Err(TransactionValidityError),
}

/// Information about a valid transaction.
#[derive(Debug, Clone, Decode)]
pub struct ValidTransaction {
	/// Priority of the transaction (higher = more likely to be included).
	pub priority: u64,
	/// Transaction dependencies (tags this tx requires).
	pub requires: Vec<Vec<u8>>,
	/// Tags this transaction provides.
	pub provides: Vec<Vec<u8>>,
	/// Longevity - how long this tx is valid (in blocks).
	pub longevity: u64,
	/// Whether this transaction should be propagated.
	pub propagate: bool,
}

/// Error when transaction validation fails.
#[derive(Debug, Clone, Decode)]
pub enum TransactionValidityError {
	/// Transaction is invalid (won't ever be valid).
	#[codec(index = 0)]
	Invalid(InvalidTransaction),
	/// Transaction validity is unknown (might become valid).
	#[codec(index = 1)]
	Unknown(UnknownTransaction),
}

/// Reasons a transaction is invalid.
#[derive(Debug, Clone, Decode)]
pub enum InvalidTransaction {
	/// General call failure.
	#[codec(index = 0)]
	Call,
	/// Payment failed (can't pay fees).
	#[codec(index = 1)]
	Payment,
	/// Future transaction (nonce too high).
	#[codec(index = 2)]
	Future,
	/// Stale transaction (nonce too low).
	#[codec(index = 3)]
	Stale,
	/// Bad mandatory inherent.
	#[codec(index = 4)]
	BadMandatory,
	/// Mandatory dispatch error.
	#[codec(index = 5)]
	MandatoryDispatch,
	/// Bad signature.
	#[codec(index = 6)]
	BadSigner,
	/// Custom error (runtime-specific).
	#[codec(index = 7)]
	Custom(u8),
}

/// Reasons transaction validity is unknown.
#[derive(Debug, Clone, Decode)]
pub enum UnknownTransaction {
	/// Can't lookup validity (dependencies missing).
	#[codec(index = 0)]
	CannotLookup,
	/// No unsigned validation handler.
	#[codec(index = 1)]
	NoUnsignedValidator,
	/// Custom unknown error.
	#[codec(index = 2)]
	Custom(u8),
}

impl TransactionValidityError {
	/// Get a human-readable reason for the error.
	pub fn reason(&self) -> String {
		match self {
			Self::Invalid(inv) => match inv {
				InvalidTransaction::Call => "Call failed".into(),
				InvalidTransaction::Payment => "Insufficient funds for fees".into(),
				InvalidTransaction::Future => "Nonce too high".into(),
				InvalidTransaction::Stale => "Nonce too low (already used)".into(),
				InvalidTransaction::BadMandatory => "Bad mandatory inherent".into(),
				InvalidTransaction::MandatoryDispatch => "Mandatory dispatch failed".into(),
				InvalidTransaction::BadSigner => "Invalid signature".into(),
				InvalidTransaction::Custom(code) => format!("Custom error: {code}"),
			},
			Self::Unknown(unk) => match unk {
				UnknownTransaction::CannotLookup => "Cannot lookup validity".into(),
				UnknownTransaction::NoUnsignedValidator => "No unsigned validator".into(),
				UnknownTransaction::Custom(code) => format!("Custom unknown: {code}"),
			},
		}
	}

	/// Check if this is an "unknown" error (might become valid later).
	pub fn is_unknown(&self) -> bool {
		matches!(self, Self::Unknown(_))
	}
}

/// Result of building a block, including information about extrinsic processing.
#[derive(Debug, Clone)]
pub struct BuildBlockResult {
	/// The newly built block.
	pub block: Block,
	/// Extrinsics that were successfully included.
	pub included: Vec<Vec<u8>>,
	/// Extrinsics that failed during apply and were dropped.
	pub failed: Vec<FailedExtrinsic>,
}

/// An extrinsic that failed during block building.
#[derive(Debug, Clone)]
pub struct FailedExtrinsic {
	/// The raw extrinsic bytes.
	pub extrinsic: Vec<u8>,
	/// Reason for failure.
	pub reason: String,
}

/// Capacity for the blockchain event broadcast channel.
const EVENT_CHANNEL_CAPACITY: usize = 256;

/// Events emitted by the blockchain when state changes.
///
/// Subscribe to these events via [`Blockchain::subscribe_events`] to receive
/// notifications when blocks are built.
#[derive(Debug, Clone)]
pub enum BlockchainEvent {
	/// A new block was built and is now the head.
	NewBlock {
		/// The new block's hash.
		hash: H256,
		/// The new block's number.
		number: u32,
		/// The parent block's hash.
		parent_hash: H256,
		/// The SCALE-encoded block header.
		header: Vec<u8>,
		/// Storage keys that were modified in this block.
		modified_keys: Vec<Vec<u8>>,
	},
}

/// Errors that can occur when working with the blockchain manager.
#[derive(Debug, thiserror::Error)]
pub enum BlockchainError {
	/// Block-related error.
	#[error(transparent)]
	Block(#[from] BlockError),

	/// Block builder error.
	#[error(transparent)]
	Builder(#[from] BlockBuilderError),

	/// Cache error.
	#[error(transparent)]
	Cache(#[from] CacheError),

	/// Executor error.
	#[error(transparent)]
	Executor(#[from] ExecutorError),
}

/// Type of chain being forked.
#[derive(Debug, Clone, PartialEq, Eq)]
pub enum ChainType {
	/// A relay chain (Polkadot, Kusama, etc.).
	RelayChain,
	/// A parachain with a specific para ID.
	Parachain {
		/// The parachain ID.
		para_id: u32,
	},
}

/// The blockchain manager for a forked chain.
///
/// `Blockchain` is the main entry point for creating local forks of live
/// Polkadot SDK chains. It manages the fork lifecycle, block building,
/// and provides APIs for querying state and executing runtime calls.
///
/// # Creating a Fork
///
/// Use [`Blockchain::fork`] to create a new fork from a live chain:
///
/// ```ignore
/// let blockchain = Blockchain::fork(&endpoint, None).await?;
/// ```
///
/// # Block Building
///
/// Build blocks using [`build_block`](Blockchain::build_block) or
/// [`build_empty_block`](Blockchain::build_empty_block):
///
/// ```ignore
/// // Build a block with user extrinsics
/// let block = blockchain.build_block(vec![signed_extrinsic]).await?;
///
/// // Build an empty block (just inherents)
/// let block = blockchain.build_empty_block().await?;
/// ```
///
/// # Querying State
///
/// Query storage at the current head or at a specific block:
///
/// ```ignore
/// // At head
/// let value = blockchain.storage(&key).await?;
///
/// // At a specific block
/// let value = blockchain.storage_at(block_hash, &key).await?;
/// ```
///
/// # Thread Safety
///
/// `Blockchain` is `Send + Sync` and can be safely shared across async tasks.
/// Internal state is protected by `RwLock`.
pub struct Blockchain {
	/// Current head block.
	head: RwLock<Block>,

	/// Inherent providers for block building.
	inherent_providers: Vec<Arc<dyn InherentProvider>>,

	/// Chain name (e.g., "Polkadot", "Asset Hub").
	chain_name: String,

	/// Chain type (relay chain or parachain).
	chain_type: ChainType,

	/// Fork point block hash.
	fork_point_hash: H256,

	/// Fork point block number.
	fork_point_number: u32,

	/// Executor configuration for runtime calls.
	executor_config: ExecutorConfig,

	/// Cached runtime executor, created once at fork time and reused across blocks.
	///
	/// Recreated only on runtime upgrade (when `:code` storage changes).
	/// The executor stores the compiled WASM runtime code and is cheap to clone
	/// (runtime code is behind an `Arc`).
	executor: RwLock<RuntimeExecutor>,

	/// Warm VM prototype for reuse across block builds.
	///
	/// A compiled WASM prototype that persists across block builds, avoiding
	/// the cost of re-parsing and re-compiling the runtime (~2.5 MB for Asset Hub)
	/// on each block. Taken before each block build and returned after finalization.
	/// Invalidated (set to `None`) on runtime upgrade.
	warm_prototype: tokio::sync::Mutex<Option<smoldot::executor::host::HostVmPrototype>>,

	/// Remote storage layer for fetching data from the live chain.
	///
	/// This maintains a persistent connection to the RPC endpoint and is shared
	/// across all blocks. All remote queries (storage, blocks, headers) go through
	/// this layer, ensuring connection reuse.
	remote: crate::RemoteStorageLayer,

	/// Guard ensuring the storage prefetch runs exactly once.
	///
	/// Both the background warmup and `build_block()` call
	/// `ensure_prefetched()`, which uses `OnceCell::get_or_init` so only the
	/// first caller runs the actual prefetch. The second caller (or any
	/// subsequent call) awaits the result and returns immediately.
	prefetch_done: OnceCell<()>,

	/// Cached slot duration in milliseconds (0 = not yet detected).
	///
	/// Computed during warmup by reusing the compiled WASM prototype for a
	/// `AuraApi_slot_duration` call. Used by `build_block()` to skip an
	/// expensive runtime call in `create_next_header_with_slot`.
	/// Reset on runtime upgrade so the next block re-detects it.
	cached_slot_duration: AtomicU64,

	/// Event broadcaster for subscription notifications.
	///
	/// Subscriptions receive events through receivers obtained via
	/// [`subscribe_events`](Blockchain::subscribe_events).
	event_tx: broadcast::Sender<BlockchainEvent>,

	/// Cached genesis hash (lazily initialized per-instance).
	///
	/// This cache is instance-specific, ensuring each forked chain maintains
	/// its own genesis hash even when multiple forks run in the same process.
	genesis_hash_cache: OnceCell<String>,

	/// Cached chain properties (lazily initialized per-instance).
	///
	/// This cache is instance-specific, ensuring each forked chain maintains
	/// its own properties even when multiple forks run in the same process.
	chain_properties_cache: OnceCell<Option<serde_json::Value>>,

	/// Epoch milliseconds of the last reconnection log at DEBUG level.
	///
	/// Used to debounce reconnection messages. When the WS connection drops
	/// during long WASM execution, concurrent RPC requests all trigger
	/// reconnection attempts simultaneously. Without debouncing, this floods
	/// the log with identical messages.
	last_reconnect_log: AtomicU64,
}

impl Blockchain {
	/// Create a new blockchain forked from a live chain.
	///
	/// This connects to the live chain, fetches the fork point block,
	/// initializes the runtime executor, and detects the chain type.
	///
	/// # Arguments
	///
	/// * `endpoint` - RPC endpoint URL of the live chain
	/// * `cache_path` - Optional path for persistent SQLite cache. If `None`, an in-memory cache is
	///   used.
	///
	/// # Returns
	///
	/// A new `Blockchain` instance ready for block building.
	///
	/// # Example
	///
	/// ```ignore
	/// use pop_fork::Blockchain;
	/// use std::path::Path;
	/// use url::Url;
	///
	/// let endpoint: Url = "wss://rpc.polkadot.io".parse()?;
	///
	/// // With in-memory cache
	/// let blockchain = Blockchain::fork(&endpoint, None).await?;
	///
	/// // With persistent cache
	/// let blockchain = Blockchain::fork(&endpoint, Some(Path::new("./cache.sqlite"))).await?;
	/// ```
	pub async fn fork(
		endpoint: &Url,
		cache_path: Option<&Path>,
	) -> Result<Arc<Self>, BlockchainError> {
		Self::fork_with_config(endpoint, cache_path, None, ExecutorConfig::default()).await
	}

	/// Create a new blockchain forked from a live chain at a specific block.
	///
	/// Similar to [`fork`](Blockchain::fork), but allows specifying the exact
	/// block to fork from.
	///
	/// # Arguments
	///
	/// * `endpoint` - RPC endpoint URL of the live chain
	/// * `cache_path` - Optional path for persistent SQLite cache
	/// * `fork_point` - Block number or hash to fork from. If `None`, uses the latest finalized
	///   block.
	///
	/// # Example
	///
	/// ```ignore
	/// // Fork at a specific block number
	/// let blockchain = Blockchain::fork_at(&endpoint, None, Some(12345678.into())).await?;
	///
	/// // Fork at a specific block hash
	/// let blockchain = Blockchain::fork_at(&endpoint, None, Some(block_hash.into())).await?;
	/// ```
	pub async fn fork_at(
		endpoint: &Url,
		cache_path: Option<&Path>,
		fork_point: Option<BlockForkPoint>,
	) -> Result<Arc<Self>, BlockchainError> {
		Self::fork_with_config(endpoint, cache_path, fork_point, ExecutorConfig::default()).await
	}

	/// Create a new blockchain forked from a live chain with custom executor configuration.
	///
	/// This is the most flexible fork method, allowing customization of both
	/// the fork point and the executor configuration.
	///
	/// # Arguments
	///
	/// * `endpoint` - RPC endpoint URL of the live chain
	/// * `cache_path` - Optional path for persistent SQLite cache
	/// * `fork_point` - Block number or hash to fork from. If `None`, uses the latest finalized
	///   block.
	/// * `executor_config` - Configuration for the runtime executor
	///
	/// # Example
	///
	/// ```ignore
	/// use pop_fork::{Blockchain, ExecutorConfig, SignatureMockMode};
	///
	/// // Fork with signature mocking enabled (useful for testing)
	/// let config = ExecutorConfig {
	///     signature_mock: SignatureMockMode::AlwaysValid,
	///     ..Default::default()
	/// };
	/// let blockchain = Blockchain::fork_with_config(&endpoint, None, None, config).await?;
	/// ```
	pub async fn fork_with_config(
		endpoint: &Url,
		cache_path: Option<&Path>,
		fork_point: Option<BlockForkPoint>,
		executor_config: ExecutorConfig,
	) -> Result<Arc<Self>, BlockchainError> {
		// Create storage cache
		let cache = StorageCache::open(cache_path).await?;

		// Determine fork point
		let fork_point = match fork_point {
			Some(fp) => fp,
			None => {
				// Get latest finalized block from RPC
				let rpc =
					crate::ForkRpcClient::connect(endpoint).await.map_err(BlockError::from)?;
				let finalized = rpc.finalized_head().await.map_err(BlockError::from)?;
				BlockForkPoint::Hash(finalized)
			},
		};

		// Create fork point block
		let fork_block = Block::fork_point(endpoint, cache, fork_point).await?;
		let fork_point_hash = fork_block.hash;
		let fork_point_number = fork_block.number;

		// Detect chain type
		let chain_type = Self::detect_chain_type(&fork_block).await?;

		// Get chain name
		let chain_name = Self::get_chain_name(&fork_block).await?;

		// Create inherent providers based on chain type
		let is_parachain = matches!(chain_type, ChainType::Parachain { .. });
		let inherent_providers = default_providers(is_parachain)
			.into_iter()
			.map(|p| Arc::from(p) as Arc<dyn InherentProvider>)
			.collect();

		// Create event broadcast channel
		let (event_tx, _) = broadcast::channel(EVENT_CHANNEL_CAPACITY);

		// Get the remote storage layer from the fork block (shares same RPC connection)
		let remote = fork_block.storage().remote().clone();

		// Create executor once with runtime code from the fork point.
		// This avoids re-validating and re-compiling the WASM on every block build.
		let runtime_code = fork_block.runtime_code().await?;
		let executor = RuntimeExecutor::with_config(runtime_code, None, executor_config.clone())?;

		log::debug!("Forked at block #{fork_point_number} (0x{})", hex::encode(fork_point_hash));

		let blockchain = Arc::new(Self {
			head: RwLock::new(fork_block),
			inherent_providers,
			chain_name,
			chain_type,
			fork_point_hash,
			fork_point_number,
			executor_config,
			executor: RwLock::new(executor),
			warm_prototype: tokio::sync::Mutex::new(None),
			prefetch_done: OnceCell::new(),
			cached_slot_duration: AtomicU64::new(0),
			remote,
			event_tx,
			genesis_hash_cache: OnceCell::new(),
			chain_properties_cache: OnceCell::new(),
			last_reconnect_log: AtomicU64::new(0),
		});

		// Spawn background warmup to pre-cache WASM prototype, storage, and
		// inherent provider state. This runs concurrently and does not delay
		// the return of the fork. If a block is built before warmup finishes,
		// the builder falls back to its normal (non-cached) path.
		// Skipped in tests to avoid resource contention when many tests run in parallel.
		#[cfg(not(test))]
		{
			let bc = Arc::clone(&blockchain);
			tokio::spawn(async move { bc.warmup().await });
		}

		Ok(blockchain)
	}

	/// Run background warmup to pre-cache expensive resources.
	///
	/// This method is designed to be spawned as a background task immediately after
	/// forking. It pre-populates caches that would otherwise cause a cold-start
	/// penalty on the first block build:
	///
	/// 1. **WASM prototype compilation** (~2-5s for large runtimes like Asset Hub). The compiled
	///    prototype is stored in `warm_prototype` for reuse by the first `build_block()` call.
	///
	/// 2. **Storage prefetch** (~1-2s). Batch-fetches all `StorageValue` keys and the first page of
	///    each pallet's storage map, populating the remote cache.
	///
	/// 3. **Inherent provider warmup**. Calls `warmup()` on each registered provider (e.g.
	///    `TimestampInherent` caches the slot duration to avoid a separate WASM execution during
	///    block building).
	///
	/// If a block is built before warmup finishes, the builder falls back to its
	/// normal (non-cached) path. The `Mutex`/`OnceCell` guards ensure no races.
	pub async fn warmup(self: &Arc<Self>) {
		let warmup_start = std::time::Instant::now();
		log::debug!("[Blockchain] Background warmup starting...");

		// 1 & 2. Compile WASM prototype and compute slot duration without holding
		// the prototype lock. The expensive work (create_prototype + WASM call) runs
		// lock-free so concurrent call_at_block() and build_block() are not blocked.
		// If build_block() runs before warmup finishes, it simply finds no cached
		// prototype and falls back to its normal path.
		let executor = self.executor.read().await.clone();
		match executor.create_prototype() {
			Ok(proto) => {
				log::debug!(
					"[Blockchain] Warmup: WASM prototype compiled ({:?})",
					warmup_start.elapsed()
				);

				// Try AuraApi_slot_duration using the warm prototype (Aura chains).
				let head = self.head.read().await;
				let (result, returned_proto) = executor
					.call_with_prototype(
						Some(proto),
						crate::strings::inherent::timestamp::slot_duration::AURA_API_METHOD,
						&[],
						head.storage(),
					)
					.await;

				let aura_duration =
					result.ok().and_then(|r| u64::decode(&mut r.output.as_slice()).ok());

				// Use the full three-tier detection: AuraApi > Babe constant > fallback.
				// This mirrors TimestampInherent::get_slot_duration_from_runtime but
				// avoids creating a redundant WASM prototype.
				let duration = if let Some(d) = aura_duration {
					d
				} else {
					let metadata = head.metadata().await.ok();
					let babe_duration = metadata.as_ref().and_then(|m| {
						use crate::strings::inherent::timestamp::slot_duration;
						m.pallet_by_name(slot_duration::BABE_PALLET)?
							.constant_by_name(slot_duration::BABE_EXPECTED_BLOCK_TIME)
							.and_then(|c| u64::decode(&mut &c.value()[..]).ok())
					});
					babe_duration.unwrap_or(match self.chain_type {
						ChainType::RelayChain => slot_duration::RELAY_CHAIN_FALLBACK_MS,
						ChainType::Parachain { .. } => slot_duration::PARACHAIN_FALLBACK_MS,
					})
				};
				drop(head);

				self.cached_slot_duration.store(duration, Ordering::Release);
				// Store prototype under a brief lock.
				*self.warm_prototype.lock().await = returned_proto;
				log::debug!(
					"[Blockchain] Warmup: slot_duration={duration}ms ({:?})",
					warmup_start.elapsed()
				);
			},
			Err(e) => log::warn!("[Blockchain] Warmup: prototype compilation failed: {e}"),
		}

		// 3. Prefetch storage (coordinated via OnceCell with build_block)
		self.ensure_prefetched().await;
		log::debug!("[Blockchain] Warmup: prefetch done ({:?})", warmup_start.elapsed());

		// 4. Warm up inherent providers
		let head = self.head.read().await.clone();
		for provider in &self.inherent_providers {
			provider.warmup(&head, &executor).await;
		}

		log::debug!("[Blockchain] Background warmup complete ({:?})", warmup_start.elapsed());
	}

	/// Ensure storage has been prefetched exactly once.
	///
	/// Uses `OnceCell` to guarantee the prefetch runs only once, even when
	/// called concurrently by the background warmup and `build_block()`.
	/// The first caller runs the actual prefetch; subsequent callers await
	/// the result and return immediately.
	async fn ensure_prefetched(&self) {
		self.prefetch_done
			.get_or_init(|| async {
				if let Err(e) = self.do_prefetch().await {
					log::warn!("[Blockchain] Storage prefetch failed (non-fatal): {e}");
				}
			})
			.await;
	}

	/// Run the actual storage prefetch.
	///
	/// Replicates the prefetch logic from `BlockBuilder` but operates directly
	/// on the `Blockchain`'s remote storage layer and head block metadata.
	async fn do_prefetch(&self) -> Result<(), BlockchainError> {
		let head = self.head.read().await;
		let metadata = head.metadata().await?;
		let block_hash = head.storage().fork_block_hash();

		// Collect StorageValue keys and pallet prefixes from metadata
		let mut value_keys: Vec<Vec<u8>> = Vec::new();
		let mut pallet_prefixes: Vec<Vec<u8>> = Vec::new();

		for pallet in metadata.pallets() {
			let pallet_hash = sp_core::twox_128(pallet.name().as_bytes());
			if let Some(storage) = pallet.storage() {
				for entry in storage.entries() {
					if matches!(
						entry.entry_type(),
						subxt::metadata::types::StorageEntryType::Plain(_)
					) {
						let entry_hash = sp_core::twox_128(entry.name().as_bytes());
						value_keys.push([pallet_hash.as_slice(), entry_hash.as_slice()].concat());
					}
				}
				pallet_prefixes.push(pallet_hash.to_vec());
			}
		}

		// Batch-fetch all StorageValue keys
		if !value_keys.is_empty() {
			let key_refs: Vec<&[u8]> = value_keys.iter().map(|k| k.as_slice()).collect();
			if let Err(e) = self.remote.get_batch(block_hash, &key_refs).await {
				log::debug!(
					"[Blockchain] Warmup: StorageValue batch fetch failed (non-fatal): {e}"
				);
			}
		}

		// Single-page pallet prefix scans in parallel
		let page_size = crate::strings::builder::PREFETCH_PAGE_SIZE;
		let scan_futures: Vec<_> = pallet_prefixes
			.iter()
			.map(|prefix| self.remote.prefetch_prefix_single_page(block_hash, prefix, page_size))
			.collect();
		let scan_results = futures::future::join_all(scan_futures).await;
		let mut scan_keys = 0usize;
		for count in scan_results.into_iter().flatten() {
			scan_keys += count;
		}

		log::debug!(
			"[Blockchain] Prefetched {} StorageValue + {} map keys ({} pallets)",
			value_keys.len(),
			scan_keys,
			pallet_prefixes.len(),
		);

		Ok(())
	}

	/// Get the chain name.
	pub fn chain_name(&self) -> &str {
		&self.chain_name
	}

	/// Get the chain type.
	pub fn chain_type(&self) -> &ChainType {
		&self.chain_type
	}

	/// Get the fork point block hash.
	pub fn fork_point(&self) -> H256 {
		self.fork_point_hash
	}

	/// Get the fork point block number.
	pub fn fork_point_number(&self) -> u32 {
		self.fork_point_number
	}

	/// Get the RPC endpoint URL.
	pub fn endpoint(&self) -> &Url {
		self.remote.endpoint()
	}

	/// Get the genesis hash, formatted as a hex string with "0x" prefix.
	///
	/// This method lazily fetches and caches the genesis hash on first call.
	/// The cache is per-instance, so each forked chain maintains its own value
	/// even when multiple forks run in the same process.
	///
	/// # Returns
	///
	/// The genesis hash as "0x" prefixed hex string, or an error if fetching fails.
	pub async fn genesis_hash(&self) -> Result<String, BlockchainError> {
		self.genesis_hash_cache
			.get_or_try_init(|| async {
				match self.block_hash_at(0).await? {
					Some(hash) => Ok(format!("0x{}", hex::encode(hash.as_bytes()))),
					None => Err(BlockchainError::Block(BlockError::RuntimeCodeNotFound)),
				}
			})
			.await
			.cloned()
	}

	/// Get the chain properties.
	///
	/// This method lazily fetches and caches the chain properties on first call.
	/// The cache is per-instance, so each forked chain maintains its own value
	/// even when multiple forks run in the same process.
	///
	/// # Returns
	///
	/// The chain properties as JSON, or `None` if not available.
	pub async fn chain_properties(&self) -> Option<serde_json::Value> {
		self.chain_properties_cache
			.get_or_init(|| async {
				match ForkRpcClient::connect(self.endpoint()).await {
					Ok(client) => match client.system_properties().await {
						Ok(system_props) => serde_json::to_value(system_props).ok(),
						Err(_) => None,
					},
					Err(_) => None,
				}
			})
			.await
			.clone()
	}

	/// Subscribe to blockchain events.
	///
	/// Returns a receiver that will get events when blocks are built.
	/// Use this for implementing reactive RPC subscriptions.
	///
	/// # Example
	///
	/// ```ignore
	/// let mut receiver = blockchain.subscribe_events();
	/// tokio::spawn(async move {
	///     while let Ok(event) = receiver.recv().await {
	///         match event {
	///             BlockchainEvent::NewBlock { hash, number, .. } => {
	///                 println!("New block #{} ({:?})", number, hash);
	///             }
	///         }
	///     }
	/// });
	/// ```
	pub fn subscribe_events(&self) -> broadcast::Receiver<BlockchainEvent> {
		self.event_tx.subscribe()
	}

	/// Get the current head block.
	pub async fn head(&self) -> Block {
		self.head.read().await.clone()
	}

	/// Get the current head block number.
	pub async fn head_number(&self) -> u32 {
		self.head.read().await.number
	}

	/// Get the current head block hash.
	pub async fn head_hash(&self) -> H256 {
		self.head.read().await.hash
	}

	/// Get block body (extrinsics) by hash.
	///
	/// This method searches for the block in three places:
	/// 1. The current head block
	/// 2. Locally-built blocks (traversing the parent chain)
	/// 3. The remote chain (for blocks at or before the fork point)
	///
	/// # Arguments
	///
	/// * `hash` - The block hash to query
	///
	/// # Returns
	///
	/// The block's extrinsics as raw bytes, or `None` if the block is not found.
	pub async fn block_body(&self, hash: H256) -> Result<Option<BlockBody>, BlockchainError> {
		// First, check if it matches any locally-built block (but not the fork point,
		// which has empty extrinsics since we don't fetch them during fork)
		let head = self.head.read().await;

		// Traverse the parent chain to find the block
		let mut current: Option<&Block> = Some(&head);
		while let Some(block) = current {
			if block.hash == hash {
				// If this is the fork point (no parent), we need to fetch from remote
				// because fork point's extrinsics are not stored locally
				if block.parent.is_none() {
					break; // Fall through to remote fetch
				}
				return Ok(Some(block.extrinsics.clone()));
			}
			current = block.parent.as_deref();
		}
		drop(head);

		// Not found locally or is fork point - fetch from remote with reconnect
		match self.remote.block_body(hash).await {
			Ok(body) => Ok(body),
			Err(first_err) =>
				if self.reconnect_upstream().await {
					Ok(self.remote.block_body(hash).await.map_err(BlockError::from)?)
				} else {
					Err(BlockchainError::Block(BlockError::from(first_err)))
				},
		}
	}

	/// Get block header by hash.
	///
	/// This method searches for the block in three places:
	/// 1. Locally-built blocks (traversing the parent chain)
	/// 2. The fork point block
	/// 3. The remote chain (for blocks at or before the fork point)
	///
	/// # Arguments
	///
	/// * `hash` - The block hash to query
	///
	/// # Returns
	///
	/// The SCALE-encoded block header, or `None` if the block is not found.
	pub async fn block_header(&self, hash: H256) -> Result<Option<Vec<u8>>, BlockchainError> {
		let head = self.head.read().await;

		// Traverse the parent chain to find the block
		let mut current: Option<&Block> = Some(&head);
		while let Some(block) = current {
			if block.hash == hash {
				return Ok(Some(block.header.clone()));
			}
			current = block.parent.as_deref();
		}
		drop(head);

		// Not found locally - fetch from remote with reconnect
		match self.remote.block_header(hash).await {
			Ok(header) => Ok(header),
			Err(first_err) =>
				if self.reconnect_upstream().await {
					Ok(self.remote.block_header(hash).await.map_err(BlockError::from)?)
				} else {
					Err(BlockchainError::Block(BlockError::from(first_err)))
				},
		}
	}

	/// Get block hash by block number.
	///
	/// This method searches for the block in three places:
	/// 1. Locally-built blocks (traversing the parent chain from head)
	/// 2. The fork point block
	/// 3. The remote chain (for blocks before the fork point)
	///
	/// # Arguments
	///
	/// * `block_number` - The block number to query
	///
	/// # Returns
	///
	/// The block hash, or `None` if the block number doesn't exist.
	pub async fn block_hash_at(&self, block_number: u32) -> Result<Option<H256>, BlockchainError> {
		// Check if block number is within our local chain range
		let head = self.head.read().await;

		if head.number < block_number {
			return Ok(None);
		}

		// Traverse the parent chain to find the block by number
		let mut current: Option<&Block> = Some(&head);
		while let Some(block) = current {
			if block.number == block_number {
				return Ok(Some(block.hash));
			}

			if block.parent.is_none() {
				break;
			}

			current = block.parent.as_deref();
		}
		drop(head);

		// Block number is before our fork point - fetch from remote with reconnect
		match self.remote.block_hash_by_number(block_number).await {
			Ok(hash) => Ok(hash),
			Err(first_err) =>
				if self.reconnect_upstream().await {
					Ok(self
						.remote
						.block_hash_by_number(block_number)
						.await
						.map_err(BlockError::from)?)
				} else {
					Err(BlockchainError::Block(BlockError::from(first_err)))
				},
		}
	}

	/// Get block number by block hash.
	///
	/// This method searches for the block in two places:
	/// 1. Locally-built blocks (traversing the parent chain from head)
	/// 2. The remote chain (for blocks at or before the fork point)
	///
	/// # Arguments
	///
	/// * `hash` - The block hash to query
	///
	/// # Returns
	///
	/// The block number, or `None` if the block hash doesn't exist.
	pub async fn block_number_by_hash(&self, hash: H256) -> Result<Option<u32>, BlockchainError> {
		// Traverse local chain to find block by hash
		let head = self.head.read().await;
		let mut current: Option<&Block> = Some(&head);
		while let Some(block) = current {
			if block.hash == hash {
				return Ok(Some(block.number));
			}
			current = block.parent.as_deref();
		}
		drop(head);

		// Not found locally - check remote with reconnect
		match self.remote.block_number_by_hash(hash).await {
			Ok(number) => Ok(number),
			Err(first_err) =>
				if self.reconnect_upstream().await {
					Ok(self.remote.block_number_by_hash(hash).await.map_err(BlockError::from)?)
				} else {
					Err(BlockchainError::Block(BlockError::from(first_err)))
				},
		}
	}

	/// Get parent hash of a block by its hash.
	///
	/// This method searches for the block in two places:
	/// 1. Locally-built blocks (traversing the parent chain from head)
	/// 2. The remote chain (for blocks at or before the fork point)
	///
	/// # Arguments
	///
	/// * `hash` - The block hash to query
	///
	/// # Returns
	///
	/// The parent block hash, or `None` if the block hash doesn't exist.
	pub async fn block_parent_hash(&self, hash: H256) -> Result<Option<H256>, BlockchainError> {
		// Traverse local chain to find block by hash
		let head = self.head.read().await;
		let mut current: Option<&Block> = Some(&head);
		while let Some(block) = current {
			if block.hash == hash {
				return Ok(Some(block.parent_hash));
			}
			current = block.parent.as_deref();
		}
		drop(head);

		// Not found locally - check remote with reconnect
		match self.remote.parent_hash(hash).await {
			Ok(parent) => Ok(parent),
			Err(first_err) =>
				if self.reconnect_upstream().await {
					Ok(self.remote.parent_hash(hash).await.map_err(BlockError::from)?)
				} else {
					Err(BlockchainError::Block(BlockError::from(first_err)))
				},
		}
	}

	/// Build a new block with the given extrinsics.
	///
	/// This creates a new block on top of the current head, applying:
	/// 1. Inherent extrinsics (timestamp, parachain validation data, etc.)
	/// 2. User-provided extrinsics
	///
	/// The new block becomes the new head.
	///
	/// # Arguments
	///
	/// * `extrinsics` - User extrinsics to include in the block
	///
	/// # Returns
	///
	/// A [`BuildBlockResult`] containing the newly created block and information
	/// about which extrinsics were successfully included vs which failed.
	///
	/// # Example
	///
	/// ```ignore
	/// let extrinsic = /* create signed extrinsic */;
	/// let result = blockchain.build_block(vec![extrinsic]).await?;
	/// println!("New block: #{} ({:?})", result.block.number, result.block.hash);
	/// println!("Included: {}, Failed: {}", result.included.len(), result.failed.len());
	/// ```
	pub async fn build_block(
		&self,
		extrinsics: BlockBody,
	) -> Result<BuildBlockResult, BlockchainError> {
		// PHASE 1: Prepare (read lock only) - get state needed for building
		let (parent_block, parent_hash) = {
			let head = self.head.read().await;
			let parent_hash = head.hash;
			(head.clone(), parent_hash)
		}; // Read lock released here

		// PHASE 2: Build (no lock held) - allows concurrent reads
		// Reuse the cached executor (created at fork time, updated on runtime upgrade)
		let executor = self.executor.read().await.clone();

		// Take the warm prototype from the cache (if available from a previous block build)
		let warm_prototype = self.warm_prototype.lock().await.take();

		// Create header for new block with automatic slot digest injection.
		// Pass cached slot duration to avoid a WASM runtime call.
		let header = create_next_header_with_slot(
			&parent_block,
			&executor,
			vec![],
			match self.cached_slot_duration.load(Ordering::Acquire) {
				0 => None,
				d => Some(d),
			},
		)
		.await?;

		// Convert Arc providers to Box for BlockBuilder
		let providers: Vec<Box<dyn InherentProvider>> = self
			.inherent_providers
			.iter()
			.map(|p| Box::new(ArcProvider(Arc::clone(p))) as Box<dyn InherentProvider>)
			.collect();

		// Ensure storage is prefetched (coordinated with background warmup via OnceCell).
		// If warmup already completed, this returns immediately. If warmup is still
		// running the prefetch, this awaits its completion. If warmup hasn't started
		// the prefetch yet, this runs it. Either way, the BlockBuilder always skips
		// its own prefetch since the Blockchain handles it.
		self.ensure_prefetched().await;

		// Create block builder with warm prototype for WASM reuse
		let mut builder = BlockBuilder::new(
			parent_block,
			executor,
			header,
			providers,
			warm_prototype,
			true, // prefetch handled above
		);

		// Initialize block
		builder.initialize().await?;

		// Apply inherents
		builder.apply_inherents().await?;

		// Track included and failed extrinsics
		let mut included = Vec::new();
		let mut failed = Vec::new();

		// Apply user extrinsics
		for extrinsic in extrinsics {
			match builder.apply_extrinsic(extrinsic.clone()).await? {
				ApplyExtrinsicResult::Success { .. } => {
					included.push(extrinsic);
				},
				ApplyExtrinsicResult::DispatchFailed { error } => {
					failed.push(FailedExtrinsic { extrinsic, reason: error });
				},
			}
		}

		// Check if a runtime upgrade occurred before finalizing, so we know
		// whether to invalidate the cached executor after finalization.
		let runtime_upgraded = builder.runtime_upgraded();

		// Finalize and get new block + warm prototype for reuse
		let (new_block, returned_prototype) = builder.finalize().await?;

		// Prepare new executor if runtime upgraded (expensive, done before locking).
		// Errors here must NOT prevent head from advancing: finalize() already
		// committed storage for the new block, so returning Err would leave the
		// fork in an inconsistent state (persisted N+1, head at N).
		let new_executor = if runtime_upgraded {
			log::debug!("[Blockchain] Runtime upgrade detected, recreating executor");
			match new_block.runtime_code().await {
				Ok(code) =>
					match RuntimeExecutor::with_config(code, None, self.executor_config.clone()) {
						Ok(executor) => Some(executor),
						Err(e) => {
							log::error!(
								"[Blockchain] Failed to recreate executor after runtime upgrade: {e}. \
							 Subsequent runtime calls may fail until the next successful upgrade."
							);
							None
						},
					},
				Err(e) => {
					log::error!(
						"[Blockchain] Failed to get runtime code after upgrade: {e}. \
						 Subsequent runtime calls may fail until the next successful upgrade."
					);
					None
				},
			}
		} else {
			None
		};

		// PHASE 3: Commit (write lock) - update head and executor atomically.
		// The prototype cache is updated after releasing the head lock to minimize
		// write-lock hold time and avoid blocking concurrent readers.
		{
			let mut head = self.head.write().await;
			// Verify parent hasn't changed (optimistic concurrency check)
			if head.hash != parent_hash {
				return Err(BlockchainError::Block(BlockError::ConcurrentBlockBuild));
			}
			*head = new_block.clone();

			// Update executor atomically with head so readers always see a
			// consistent (head, executor) pair during runtime upgrades.
			if let Some(executor) = new_executor {
				*self.executor.write().await = executor;
			}
			if runtime_upgraded {
				// Invalidate caches regardless of whether executor recreation succeeded.
				self.cached_slot_duration.store(0, Ordering::Release);
			}
		}

		// Update warm prototype outside the head lock (brief mutex acquisition).
		if runtime_upgraded {
			*self.warm_prototype.lock().await = None;
			// Invalidate inherent provider caches so stale slot durations
			// are not carried forward after a runtime upgrade.
			for provider in &self.inherent_providers {
				provider.invalidate_cache();
			}
		} else {
			*self.warm_prototype.lock().await = returned_prototype;
		}

		// Get modified keys from storage diff
		let modified_keys: Vec<Vec<u8>> = new_block
			.storage()
			.diff()
			.map(|diff| diff.into_iter().map(|(k, _)| k).collect())
			.unwrap_or_default();

		// Emit event AFTER releasing lock (ignore errors - no subscribers is OK)
		let subscribers = self.event_tx.receiver_count();
		log::debug!(
			"[Blockchain] Emitting NewBlock #{} event ({} modified keys, {} subscribers, {} header bytes)",
			new_block.number,
			modified_keys.len(),
			subscribers,
			new_block.header.len(),
		);
		let _ = self.event_tx.send(BlockchainEvent::NewBlock {
			hash: new_block.hash,
			number: new_block.number,
			parent_hash: new_block.parent_hash,
			header: new_block.header.clone(),
			modified_keys,
		});

		Ok(BuildBlockResult { block: new_block, included, failed })
	}

	/// Build an empty block (just inherents, no user extrinsics).
	///
	/// This is useful for advancing the chain state without any user
	/// transactions.
	///
	/// # Returns
	///
	/// The newly created block.
	pub async fn build_empty_block(&self) -> Result<Block, BlockchainError> {
		self.build_block(vec![]).await.map(|result| result.block)
	}

	/// Execute a runtime call at the current head.
	///
	/// # Arguments
	///
	/// * `method` - Runtime API method name (e.g., "Core_version")
	/// * `args` - SCALE-encoded arguments
	///
	/// # Returns
	///
	/// The SCALE-encoded result from the runtime.
	pub async fn call(&self, method: &str, args: &[u8]) -> Result<Vec<u8>, BlockchainError> {
		let head_hash = self.head_hash().await;
		self.call_at_block(head_hash, method, args)
			.await
			.map(|result| result.expect("head_hash always exists; qed;"))
	}

	/// Get storage value at the current head.
	///
	/// # Arguments
	///
	/// * `key` - Storage key
	///
	/// # Returns
	///
	/// The storage value, or `None` if the key doesn't exist.
	pub async fn storage(&self, key: &[u8]) -> Result<Option<Vec<u8>>, BlockchainError> {
		let block_number = self.head.read().await.number;
		self.get_storage_value(block_number, key).await
	}

	/// Get storage value at a specific block number.
	///
	/// # Arguments
	///
	/// * `block_number` - Block number to query at
	/// * `key` - Storage key
	///
	/// # Returns
	///
	/// The storage value, or `None` if the key doesn't exist.
	pub async fn storage_at(
		&self,
		block_number: u32,
		key: &[u8],
	) -> Result<Option<Vec<u8>>, BlockchainError> {
		self.get_storage_value(block_number, key).await
	}

	/// Get paginated storage keys matching a prefix at a given block.
	///
	/// If `at` is `None`, defaults to the current head block hash so that
	/// newly created keys are visible to callers such as polkadot.js.
	///
	/// For fork-local blocks, the full key set is obtained by merging remote
	/// keys (at the fork point) with local modifications, then applying
	/// pagination. For pre-fork blocks, delegates to the upstream RPC.
	pub async fn storage_keys_paged(
		&self,
		prefix: &[u8],
		count: u32,
		start_key: Option<&[u8]>,
		at: Option<H256>,
	) -> Result<Vec<Vec<u8>>, BlockchainError> {
		let block_hash = match at {
			Some(h) => h,
			None => self.head_hash().await,
		};
		log::debug!(
			"storage_keys_paged: prefix=0x{} count={} start_key={} at={:?}",
			hex::encode(prefix),
			count,
			start_key
				.map(|k| format!("0x{}", hex::encode(k)))
				.unwrap_or_else(|| "None".into()),
			block_hash,
		);

		let block_number = self.block_number_by_hash(block_hash).await?;

		if let Some(n) = block_number.filter(|&n| n > self.fork_point_number) {
			// Fork-local block: merge remote + local keys, then paginate in-memory.
			let all_keys = {
				let head = self.head.read().await;
				head.storage()
					.keys_by_prefix(prefix, n)
					.await
					.map_err(|e| BlockchainError::Block(BlockError::Storage(e)))?
			};
			// BTreeSet already returns sorted keys; apply start_key + count.
			let keys: Vec<Vec<u8>> = all_keys
				.into_iter()
				.filter(|k| start_key.is_none_or(|sk| k.as_slice() > sk))
				.take(count as usize)
				.collect();
			log::debug!("storage_keys_paged: returned {} keys (fork-local)", keys.len());
			Ok(keys)
		} else {
			let head = self.head.read().await;
			let rpc = head.storage().remote().rpc();
			match rpc.storage_keys_paged(prefix, count, start_key, block_hash).await {
				Ok(keys) => {
					log::debug!("storage_keys_paged: returned {} keys", keys.len());
					Ok(keys)
				},
				Err(first_err) => {
					drop(head);
					if self.reconnect_upstream().await {
						let head = self.head.read().await;
						let rpc = head.storage().remote().rpc();
						let keys = rpc
							.storage_keys_paged(prefix, count, start_key, block_hash)
							.await
							.map_err(|e| BlockchainError::Block(BlockError::Rpc(e)))?;
						log::debug!(
							"storage_keys_paged: returned {} keys (after reconnect)",
							keys.len()
						);
						Ok(keys)
					} else {
						Err(BlockchainError::Block(BlockError::Rpc(first_err)))
					}
				},
			}
		}
	}

	/// Get all storage keys matching a prefix, with prefetching.
	/// Enumerate all storage keys matching a prefix at a given block.
	///
	/// For pre-fork blocks, delegates to the remote RPC's `get_keys` method.
	/// For fork-local blocks, merges remote keys (at the fork point) with local
	/// modifications so that keys added or deleted after the fork are visible.
	///
	/// `at` is the block hash whose state should be scanned for keys.
	pub async fn storage_keys_by_prefix(
		&self,
		prefix: &[u8],
		at: H256,
	) -> Result<Vec<Vec<u8>>, BlockchainError> {
		log::debug!(
			"storage_keys_by_prefix: prefix=0x{} ({} bytes) at={:?}",
			hex::encode(prefix),
			prefix.len(),
			at,
		);

		let block_number = self.block_number_by_hash(at).await?;

		let keys = if let Some(n) = block_number.filter(|&n| n > self.fork_point_number) {
			// Fork-local block: merge remote + local keys using persisted state.
			let head = self.head.read().await;
			head.storage()
				.keys_by_prefix(prefix, n)
				.await
				.map_err(|e| BlockchainError::Block(BlockError::Storage(e)))?
		} else {
			let head = self.head.read().await;
			head.storage()
				.remote()
				.get_keys(at, prefix)
				.await
				.map_err(|e| BlockchainError::Block(BlockError::RemoteStorage(e)))?
		};

		log::debug!(
			"storage_keys_by_prefix: returned {} keys for prefix=0x{}",
			keys.len(),
			hex::encode(prefix)
		);
		Ok(keys)
	}

	/// Internal helper to query storage at a specific block number.
	///
	/// Accesses the shared `LocalStorageLayer` via the head block.
	/// All blocks share the same storage layer, so we use head as the accessor and let
	/// `LocalStorageLayer` handle the request.
	async fn get_storage_value(
		&self,
		block_number: u32,
		key: &[u8],
	) -> Result<Option<Vec<u8>>, BlockchainError> {
		let head = self.head.read().await;
		match head.storage().get(block_number, key).await {
			Ok(value) => Ok(value.and_then(|v| v.value.clone())),
			Err(first_err) => {
				// Connection may have dropped, reconnect and retry once.
				if self.reconnect_upstream().await {
					let value =
						head.storage().get(block_number, key).await.map_err(BlockError::from)?;
					Ok(value.and_then(|v| v.value.clone()))
				} else {
					Err(BlockchainError::Block(BlockError::from(first_err)))
				}
			},
		}
	}

	/// Detect chain type by checking for ParachainSystem pallet and extracting para_id.
	async fn detect_chain_type(block: &Block) -> Result<ChainType, BlockchainError> {
		let metadata = block.metadata().await?;

		// Check for ParachainSystem pallet (indicates this is a parachain)
		if metadata.pallet_by_name("ParachainSystem").is_some() {
			// Extract para_id from ParachainInfo pallet storage
			let para_id = Self::get_para_id(block).await.unwrap_or(0);
			Ok(ChainType::Parachain { para_id })
		} else {
			Ok(ChainType::RelayChain)
		}
	}

	/// Get the parachain ID from ParachainInfo pallet storage.
	///
	/// The para_id is stored at: `twox_128("ParachainInfo") ++ twox_128("ParachainId")`
	async fn get_para_id(block: &Block) -> Option<u32> {
		use scale::Decode;

		// Compute storage key: ParachainInfo::ParachainId
		let pallet_hash = sp_core::twox_128(storage_keys::PARACHAIN_INFO_PALLET);
		let storage_hash = sp_core::twox_128(storage_keys::PARACHAIN_ID);
		let key: Vec<u8> = [pallet_hash.as_slice(), storage_hash.as_slice()].concat();

		// Query storage
		let value = block.storage().get(block.number, &key).await.ok().flatten()?;

		value.value.as_ref().map(|value| u32::decode(&mut value.as_slice()).ok())?
	}

	/// Get chain name from runtime version.
	async fn get_chain_name(block: &Block) -> Result<String, BlockchainError> {
		// Get runtime code and create executor
		let runtime_code = block.runtime_code().await?;
		let executor = RuntimeExecutor::new(runtime_code, None)?;

		// Get runtime version which contains the spec name
		let version = executor.runtime_version()?;
		Ok(version.spec_name)
	}

	/// Execute a runtime call at a specific block hash.
	///
	/// # Arguments
	///
	/// * `hash` - The block hash to execute at
	/// * `method` - Runtime API method name (e.g., "Core_version")
	/// * `args` - SCALE-encoded arguments
	///
	/// # Returns
	///
	/// * `Ok(Some(result))` - Call succeeded at the specified block
	/// * `Ok(None)` - Block hash not found
	/// * `Err(_)` - Call failed (runtime error, storage error, etc.)
	pub async fn call_at_block(
		&self,
		hash: H256,
		method: &str,
		args: &[u8],
	) -> Result<Option<Vec<u8>>, BlockchainError> {
		// Fast path: head block reuses the warm prototype (avoids ~5s WASM recompilation)
		let head_block = {
			let head = self.head.read().await;
			(hash == head.hash).then(|| head.clone())
		};
		if let Some(head_block) = head_block {
			let pre_call_hash = head_block.hash;
			let executor = self.executor.read().await.clone();
			let warm_prototype = self.warm_prototype.lock().await.take();
			let (result, returned_prototype) = executor
				.call_with_prototype(warm_prototype, method, args, head_block.storage())
				.await;
			// Only restore the prototype if head hasn't changed (e.g., runtime upgrade).
			// A concurrent build_block may have invalidated the cache; restoring a
			// prototype compiled from old :code would cause stale execution.
			if self.head.read().await.hash == pre_call_hash {
				*self.warm_prototype.lock().await = returned_prototype;
			}
			return Ok(Some(result?.output));
		}

		// Slow path: historical/non-head blocks need a fresh executor
		let block = self.find_or_create_block_for_call(hash).await?;

		let Some(block) = block else {
			return Ok(None); // Block not found
		};

		let runtime_code = block.runtime_code().await?;
		let executor =
			RuntimeExecutor::with_config(runtime_code, None, self.executor_config.clone())?;
		let result = executor.call(method, args, block.storage()).await?;
		Ok(Some(result.output))
	}

	/// Batch-fetch storage values from the upstream at a given block.
	///
	/// Uses the remote storage layer's batch fetch, which checks the cache first and
	/// fetches only uncached keys in a single upstream RPC call. This is significantly
	/// faster than fetching each key individually.
	///
	/// Automatically reconnects to the upstream if the connection has dropped.
	pub async fn storage_batch(
		&self,
		at: H256,
		keys: &[&[u8]],
	) -> Result<Vec<Option<Vec<u8>>>, BlockchainError> {
		match self.remote.get_batch(at, keys).await {
			Ok(result) => Ok(result),
			Err(first_err) => {
				// Connection may have dropped, reconnect and retry once
				if self.reconnect_upstream().await {
					self.remote
						.get_batch(at, keys)
						.await
						.map_err(|e| BlockchainError::Block(BlockError::RemoteStorage(e)))
				} else {
					Err(BlockchainError::Block(BlockError::RemoteStorage(first_err)))
				}
			},
		}
	}

	/// Proxy a runtime API call to the upstream RPC endpoint.
	///
	/// This forwards the call to the upstream node at the given block, which has a
	/// JIT-compiled runtime and handles computationally expensive calls (like metadata
	/// generation) much faster than the local WASM interpreter.
	///
	/// Automatically reconnects if the upstream connection has dropped.
	pub async fn proxy_state_call(
		&self,
		method: &str,
		args: &[u8],
		at: H256,
	) -> Result<Vec<u8>, BlockchainError> {
		let rpc = self.remote.rpc();
		match rpc.state_call(method, args, Some(at)).await {
			Ok(result) => Ok(result),
			Err(first_err) => {
				// Connection may have dropped, reconnect and retry once
				if self.reconnect_upstream().await {
					rpc.state_call(method, args, Some(at))
						.await
						.map_err(|e| BlockchainError::Block(BlockError::from(e)))
				} else {
					Err(BlockchainError::Block(BlockError::from(first_err)))
				}
			},
		}
	}

	/// Attempt to reconnect the upstream RPC client.
	///
	/// Logs at DEBUG level at most once per `RECONNECT_LOG_DEBOUNCE_SECS` seconds.
	/// More frequent reconnection attempts are logged at TRACE to avoid flooding
	/// the console when the WS connection drops during long WASM execution.
	///
	/// Returns `true` if reconnection succeeded.
	async fn reconnect_upstream(&self) -> bool {
		let now_ms = std::time::SystemTime::now()
			.duration_since(std::time::UNIX_EPOCH)
			.map(|d| d.as_millis() as u64)
			.unwrap_or(0);
		let last = self.last_reconnect_log.load(Ordering::Relaxed);
		let elapsed_secs = now_ms.saturating_sub(last) / 1000;

		if elapsed_secs >= RECONNECT_LOG_DEBOUNCE_SECS {
			self.last_reconnect_log.store(now_ms, Ordering::Relaxed);
			log::debug!(
				"Upstream connection lost, reconnecting to {}",
				self.remote.rpc().endpoint()
			);
		} else {
			log::trace!(
				"Upstream connection lost, reconnecting to {}",
				self.remote.rpc().endpoint()
			);
		}

		self.remote.rpc().reconnect().await.is_ok()
	}

	/// Validate an extrinsic before pool submission.
	///
	/// Calls `TaggedTransactionQueue_validate_transaction` runtime API to check
	/// if the extrinsic is valid for inclusion in a future block.
	///
	/// # Arguments
	///
	/// * `extrinsic` - The encoded extrinsic to validate
	///
	/// # Returns
	///
	/// * `Ok(ValidTransaction)` - Transaction is valid with priority/dependency info
	/// * `Err(TransactionValidityError)` - Transaction is invalid or unknown
	///
	/// # Example
	///
	/// ```ignore
	/// match blockchain.validate_extrinsic(&extrinsic_bytes).await {
	///     Ok(valid) => println!("Valid with priority {}", valid.priority),
	///     Err(TransactionValidityError::Invalid(inv)) => {
	///         println!("Invalid: {:?}", inv);
	///     }
	///     Err(TransactionValidityError::Unknown(unk)) => {
	///         println!("Unknown validity: {:?}", unk);
	///     }
	/// }
	/// ```
	pub async fn validate_extrinsic(
		&self,
		extrinsic: &[u8],
	) -> Result<ValidTransaction, TransactionValidityError> {
		// Clone head and release the read lock before the async call to avoid
		// blocking build_block() from acquiring the write lock.
		let head = self.head.read().await.clone();

		// Build args: (source, extrinsic, block_hash)
		// source = External (0x02) - transaction comes from outside
		// Note: Raw concatenation matches how the runtime expects the input.
		// The extrinsic is passed as-is since it already includes its SCALE encoding.
		let mut args = Vec::with_capacity(1 + extrinsic.len() + 32);
		args.push(transaction_source::EXTERNAL);
		args.extend(extrinsic);
		args.extend(head.hash.as_bytes());

		// Reuse the cached executor and warm prototype (avoids WASM recompilation)
		let pre_call_hash = head.hash;
		let executor = self.executor.read().await.clone();
		let warm_prototype = self.warm_prototype.lock().await.take();

		// Call runtime API with warm prototype for fast validation
		let (result, returned_prototype) = executor
			.call_with_prototype(
				warm_prototype,
				runtime_api::TAGGED_TRANSACTION_QUEUE_VALIDATE,
				&args,
				head.storage(),
			)
			.await;
		// Only restore if head hasn't changed (guards against runtime upgrade race).
		if self.head.read().await.hash == pre_call_hash {
			*self.warm_prototype.lock().await = returned_prototype;
		}

		let result = result
			.map_err(|_| TransactionValidityError::Unknown(UnknownTransaction::CannotLookup))?;

		// Decode result
		let validity = TransactionValidity::decode(&mut result.output.as_slice())
			.map_err(|_| TransactionValidityError::Unknown(UnknownTransaction::CannotLookup))?;

		match validity {
			TransactionValidity::Ok(valid) => Ok(valid),
			TransactionValidity::Err(err) => Err(err),
		}
	}

	/// Find a block by hash in fork history, or create a mocked block for historical execution.
	///
	/// Returns:
	/// - `Some(block)` if found in fork history or exists on remote chain
	/// - `None` if block doesn't exist anywhere
	async fn find_or_create_block_for_call(
		&self,
		hash: H256,
	) -> Result<Option<Block>, BlockchainError> {
		let head = self.head.read().await;

		// Search fork history
		let mut current: Option<&Block> = Some(&head);
		while let Some(block) = current {
			if block.hash == hash {
				return Ok(Some(block.clone()));
			}
			// Stop at fork point - anything before this is on remote chain
			if block.parent.is_none() {
				break;
			}
			current = block.parent.as_deref();
		}

		// Not in fork history - check if block exists on remote chain via storage layer
		let block_number =
			match self.remote.block_number_by_hash(hash).await.map_err(BlockError::from)? {
				Some(number) => number,
				None => return Ok(None), // Block doesn't exist anywhere
			};

		// Block exists on remote - create mocked block with real hash and number
		// Storage layer delegates to remote for historical data
		Ok(Some(Block::mocked_for_call(hash, block_number, head.storage().clone())))
	}

	/// Set storage value at the current head (for testing purposes).
	///
	/// This method allows tests to manually set storage values to create
	/// differences between blocks for testing storage diff functionality.
	///
	/// # Arguments
	///
	/// * `key` - Storage key
	/// * `value` - Value to set, or `None` to delete
	///
	/// # Returns
	///
	/// `Ok(())` on success, or an error if storage modification fails.
	#[cfg(test)]
	pub async fn set_storage_for_testing(&self, key: &[u8], value: Option<&[u8]>) {
		let mut head = self.head.write().await;
		head.storage_mut().set(key, value).unwrap();
	}

	/// Fund well-known dev accounts and optionally set the first account as sudo.
	///
	/// Detects the chain type from the `isEthereum` chain property:
	/// - **Ethereum chains**: funds Alith, Baltathar, Charleth, Dorothy, Ethan, Faith (20-byte H160
	///   accounts)
	/// - **Substrate chains**: funds Alice, Bob, Charlie, Dave, Eve, Ferdie (32-byte sr25519
	///   accounts)
	///
	/// For each account:
	/// - If it already exists on-chain, patches its free balance
	/// - If it does not exist, creates a fresh `AccountInfo`
	///
	/// If the chain has a `Sudo` pallet, sets the first dev account as sudo.
	pub async fn initialize_dev_accounts(&self) -> Result<(), BlockchainError> {
		use crate::dev::{
			DEV_BALANCE, ETHEREUM_DEV_ACCOUNTS, SUBSTRATE_DEV_ACCOUNTS, account_storage_key,
			build_account_info, patch_free_balance, sudo_key_storage_key,
		};

		// Check isEthereum property before acquiring the write lock.
		let is_ethereum = self
			.chain_properties()
			.await
			.and_then(|props| props.get("isEthereum")?.as_bool())
			.unwrap_or(false);

		let mut head = self.head.write().await;

		// Pick the right account set for the chain type.
		let accounts: Vec<(&str, Vec<u8>)> = if is_ethereum {
			ETHEREUM_DEV_ACCOUNTS.iter().map(|(n, a)| (*n, a.to_vec())).collect()
		} else {
			SUBSTRATE_DEV_ACCOUNTS.iter().map(|(n, a)| (*n, a.to_vec())).collect()
		};

		// Build all storage keys upfront.
		let keys: Vec<Vec<u8>> = accounts.iter().map(|(_, a)| account_storage_key(a)).collect();
		let key_refs: Vec<&[u8]> = keys.iter().map(|k| k.as_slice()).collect();

		// Batch-fetch existing account data in a single RPC call.
		let existing_values = head
			.storage()
			.remote()
			.get_batch(self.fork_point_hash, &key_refs)
			.await
			.map_err(BlockError::from)?;

		// Build funded account entries and write them all at once.
		let entries: Vec<(&[u8], Option<Vec<u8>>)> = keys
			.iter()
			.zip(existing_values.iter())
			.map(|(key, existing)| {
				let value = match existing {
					Some(data) => patch_free_balance(data, DEV_BALANCE),
					None => build_account_info(DEV_BALANCE),
				};
				(key.as_slice(), Some(value))
			})
			.collect();

		let batch: Vec<(&[u8], Option<&[u8]>)> =
			entries.iter().map(|(k, v)| (*k, v.as_deref())).collect();
		head.storage_mut().set_batch_initial(&batch).map_err(BlockError::from)?;

		for (name, addr) in &accounts {
			log::debug!("Funded dev account: {name} (0x{})", hex::encode(addr));
		}

		// Set the first dev account as sudo if the Sudo pallet exists.
		let metadata = head.metadata().await?;
		if metadata.pallet_by_name("Sudo").is_some() {
			let key = sudo_key_storage_key();
			let sudo_account = &accounts[0].1;
			head.storage_mut()
				.set_initial(&key, Some(sudo_account))
				.map_err(BlockError::from)?;
			log::debug!("Set {} as sudo key (0x{})", accounts[0].0, hex::encode(&accounts[0].1));
		}

		Ok(())
	}

	/// Clear all locally tracked storage data from the cache.
	///
	/// This removes all key-value pairs that were created during block building
	/// (stored in the `local_keys` and `local_values` tables). Remote chain data
	/// that was fetched and cached remains intact.
	///
	/// Call this during shutdown to clean up local storage state.
	///
	/// # Returns
	///
	/// `Ok(())` on success, or a cache error if the operation fails.
	pub async fn clear_local_storage(&self) -> Result<(), CacheError> {
		let head = self.head.read().await;
		head.storage().cache().clear_local_storage().await
	}
}

/// Wrapper to convert `Arc<dyn InherentProvider>` to `Box<dyn InherentProvider>`.
///
/// This is needed because `BlockBuilder` expects `Box<dyn InherentProvider>`,
/// but we store providers as `Arc` for sharing across builds.
struct ArcProvider(Arc<dyn InherentProvider>);

#[async_trait::async_trait]
impl InherentProvider for ArcProvider {
	fn identifier(&self) -> &'static str {
		self.0.identifier()
	}

	async fn provide(
		&self,
		parent: &Block,
		executor: &RuntimeExecutor,
	) -> Result<Vec<Vec<u8>>, BlockBuilderError> {
		self.0.provide(parent, executor).await
	}
}

#[cfg(test)]
mod tests {
	use super::*;

	#[test]
	fn blockchain_error_display() {
		let err = BlockchainError::Block(BlockError::RuntimeCodeNotFound);
		assert!(err.to_string().contains("Runtime code not found"));
	}

	/// Integration tests that execute Blockchain against a local test node.
	///
	/// These tests verify the full blockchain lifecycle including fork creation,
	/// block building, storage queries, and runtime calls.
	mod sequential {
		use super::*;
		use crate::testing::{
			TestContext,
			accounts::{ALICE, BOB},
			constants::TRANSFER_AMOUNT,
			helpers::{account_storage_key, build_mock_signed_extrinsic_v4, decode_free_balance},
		};

		#[tokio::test(flavor = "multi_thread")]
		async fn fork_creates_blockchain_with_correct_fork_point() {
			let ctx = TestContext::minimal().await;

			let blockchain =
				Blockchain::fork(&ctx.endpoint, None).await.expect("Failed to fork blockchain");

			// Fork point should be set
			assert!(blockchain.fork_point_number() > 0 || blockchain.fork_point_number() == 0);
			assert_ne!(blockchain.fork_point(), H256::zero());

			// Head should match fork point initially
			assert_eq!(blockchain.head_number().await, blockchain.fork_point_number());
			assert_eq!(blockchain.head_hash().await, blockchain.fork_point());
		}

		#[tokio::test(flavor = "multi_thread")]
		async fn fork_at_creates_blockchain_at_specific_block() {
			let ctx = TestContext::minimal().await;

			// First fork to get the current block number
			let blockchain =
				Blockchain::fork(&ctx.endpoint, None).await.expect("Failed to fork blockchain");

			let fork_number = blockchain.fork_point_number();

			// Fork at a specific block number (same as current for test node)
			let blockchain2 = Blockchain::fork_at(&ctx.endpoint, None, Some(fork_number.into()))
				.await
				.expect("Failed to fork at specific block");

			assert_eq!(blockchain2.fork_point_number(), fork_number);
		}

		#[tokio::test(flavor = "multi_thread")]
		async fn fork_with_invalid_endpoint_fails() {
			let invalid_endpoint: Url = "ws://localhost:19999".parse().unwrap();

			let result = Blockchain::fork(&invalid_endpoint, None).await;

			assert!(result.is_err());
		}

		#[tokio::test(flavor = "multi_thread")]
		async fn fork_at_with_invalid_block_number_fails() {
			let ctx = TestContext::minimal().await;

			let result = Blockchain::fork_at(&ctx.endpoint, None, Some(u32::MAX.into())).await;

			assert!(result.is_err());
		}

		#[tokio::test(flavor = "multi_thread")]
		async fn fork_detects_relay_chain_type() {
			let ctx = TestContext::minimal().await;

			let blockchain =
				Blockchain::fork(&ctx.endpoint, None).await.expect("Failed to fork blockchain");

			// Test node is a relay chain (no ParachainSystem pallet)
			assert_eq!(*blockchain.chain_type(), ChainType::RelayChain);
		}

		#[tokio::test(flavor = "multi_thread")]
		async fn fork_retrieves_chain_name() {
			let ctx = TestContext::minimal().await;

			let blockchain =
				Blockchain::fork(&ctx.endpoint, None).await.expect("Failed to fork blockchain");

			// Chain name should not be empty
			assert!(!blockchain.chain_name().is_empty());
		}

		#[tokio::test(flavor = "multi_thread")]
		async fn build_empty_block_advances_chain() {
			let ctx = TestContext::minimal().await;

			let blockchain =
				Blockchain::fork(&ctx.endpoint, None).await.expect("Failed to fork blockchain");

			let initial_number = blockchain.head_number().await;
			let initial_hash = blockchain.head_hash().await;

			// Build an empty block
			let new_block =
				blockchain.build_empty_block().await.expect("Failed to build empty block");

			// Block number should increment
			assert_eq!(new_block.number, initial_number + 1);

			// Head should be updated
			assert_eq!(blockchain.head_number().await, initial_number + 1);
			assert_ne!(blockchain.head_hash().await, initial_hash);

			// Parent hash should point to previous head
			assert_eq!(new_block.parent_hash, initial_hash);
		}

		#[tokio::test(flavor = "multi_thread")]
		async fn build_multiple_empty_blocks_creates_chain() {
			let ctx = TestContext::minimal().await;

			let blockchain =
				Blockchain::fork(&ctx.endpoint, None).await.expect("Failed to fork blockchain");

			let fork_number = blockchain.fork_point_number();

			// Build 3 empty blocks
			for i in 1..=3 {
				let block =
					blockchain.build_empty_block().await.expect("Failed to build empty block");

				assert_eq!(block.number, fork_number + i);
			}

			assert_eq!(blockchain.head_number().await, fork_number + 3);
		}

		#[tokio::test(flavor = "multi_thread")]
		async fn storage_returns_value_for_existing_key() {
			let ctx = TestContext::minimal().await;

			let blockchain =
				Blockchain::fork(&ctx.endpoint, None).await.expect("Failed to fork blockchain");

			// Query System::Number storage (should exist)
			let key = {
				let mut k = Vec::new();
				k.extend(sp_core::twox_128(b"System"));
				k.extend(sp_core::twox_128(b"Number"));
				k
			};

			let value = blockchain.storage(&key).await.expect("Failed to query storage");

			assert!(value.is_some());
		}

		#[tokio::test(flavor = "multi_thread")]
		async fn storage_returns_none_for_nonexistent_key() {
			let ctx = TestContext::minimal().await;

			let blockchain =
				Blockchain::fork(&ctx.endpoint, None).await.expect("Failed to fork blockchain");

			let nonexistent_key = b"nonexistent_key_12345";

			let value = blockchain.storage(nonexistent_key).await.expect("Failed to query storage");

			assert!(value.is_none());
		}

		#[tokio::test(flavor = "multi_thread")]
		async fn storage_at_queries_specific_block() {
			let ctx = TestContext::minimal().await;

			let blockchain =
				Blockchain::fork(&ctx.endpoint, None).await.expect("Failed to fork blockchain");

			let fork_number = blockchain.fork_point_number();

			// Build a block to have multiple blocks
			blockchain.build_empty_block().await.expect("Failed to build block");

			// Query storage at fork point
			let key = {
				let mut k = Vec::new();
				k.extend(sp_core::twox_128(b"System"));
				k.extend(sp_core::twox_128(b"Number"));
				k
			};

			let value = blockchain
				.storage_at(fork_number, &key)
				.await
				.expect("Failed to query storage at block");

			assert!(value.is_some());
		}

		#[tokio::test(flavor = "multi_thread")]
		async fn call_executes_runtime_api() {
			let ctx = TestContext::minimal().await;

			let blockchain =
				Blockchain::fork(&ctx.endpoint, None).await.expect("Failed to fork blockchain");

			// Call Core_version runtime API
			let result =
				blockchain.call("Core_version", &[]).await.expect("Failed to call runtime API");

			// Result should not be empty (contains version info)
			assert!(!result.is_empty());
		}

		#[tokio::test(flavor = "multi_thread")]
		async fn head_returns_current_block() {
			let ctx = TestContext::minimal().await;

			let blockchain =
				Blockchain::fork(&ctx.endpoint, None).await.expect("Failed to fork blockchain");

			let head = blockchain.head().await;

			assert_eq!(head.number, blockchain.head_number().await);
			assert_eq!(head.hash, blockchain.head_hash().await);
		}

		#[tokio::test(flavor = "multi_thread")]
		async fn head_updates_after_building_block() {
			let ctx = TestContext::minimal().await;

			let blockchain =
				Blockchain::fork(&ctx.endpoint, None).await.expect("Failed to fork blockchain");

			let old_head = blockchain.head().await;

			blockchain.build_empty_block().await.expect("Failed to build block");

			let new_head = blockchain.head().await;

			assert_eq!(new_head.number, old_head.number + 1);
			assert_ne!(new_head.hash, old_head.hash);
			assert_eq!(new_head.parent_hash, old_head.hash);
		}

		/// End-to-end integration test demonstrating the full blockchain manager flow.
		///
		/// This test shows how the blockchain manager integrates with all underlying
		/// modules (Block, BlockBuilder, LocalStorageLayer, RuntimeExecutor) to process
		/// a signed balance transfer transaction:
		///
		/// 1. Fork a live chain with signature mocking enabled
		/// 2. Query initial account balances via storage
		/// 3. Build a signed extrinsic (balance transfer from Alice to Bob)
		/// 4. Build a block containing the transaction
		/// 5. Verify the new block state reflects the transfer
		#[tokio::test(flavor = "multi_thread")]
		async fn build_block_with_signed_transfer_updates_balances() {
			use crate::{ExecutorConfig, SignatureMockMode};
			use scale::{Compact, Encode};

			let ctx = TestContext::minimal().await;

			// Fork with signature mocking enabled
			let config = ExecutorConfig {
				signature_mock: SignatureMockMode::AlwaysValid,
				..Default::default()
			};
			let blockchain = Blockchain::fork_with_config(&ctx.endpoint, None, None, config)
				.await
				.expect("Failed to fork blockchain");

			// Get storage keys for Alice and Bob
			let alice_key = account_storage_key(&ALICE);
			let bob_key = account_storage_key(&BOB);

			// Get head block for metadata and capture block number before building
			let head = blockchain.head().await;
			let head_number_before = head.number;
			let metadata = head.metadata().await.expect("Failed to get metadata");

			// Query initial balances at the current head block
			let alice_balance_before = blockchain
				.storage_at(head_number_before, &alice_key)
				.await
				.expect("Failed to get Alice balance")
				.map(|v| decode_free_balance(&v))
				.expect("Alice should have a balance");

			let bob_balance_before = blockchain
				.storage_at(head_number_before, &bob_key)
				.await
				.expect("Failed to get Bob balance")
				.map(|v| decode_free_balance(&v))
				.expect("Bob should have a balance");
			let balances_pallet =
				metadata.pallet_by_name("Balances").expect("Balances pallet should exist");
			let pallet_index = balances_pallet.index();
			let transfer_call = balances_pallet
				.call_variant_by_name("transfer_keep_alive")
				.expect("transfer_keep_alive call should exist");
			let call_index = transfer_call.index;

			// Encode the call: Balances.transfer_keep_alive(Bob, 100 units)
			let mut call_data = vec![pallet_index, call_index];
			call_data.push(0x00); // MultiAddress::Id variant
			call_data.extend(BOB);
			call_data.extend(Compact(TRANSFER_AMOUNT).encode());

			// Build a signed extrinsic
			let extrinsic = build_mock_signed_extrinsic_v4(&call_data);

			// Build a block with the transfer extrinsic
			let result = blockchain
				.build_block(vec![extrinsic])
				.await
				.expect("Failed to build block with transfer");

			let new_block = result.block;

			// Verify block was created
			assert_eq!(new_block.number, head_number_before + 1);

			// Query balances after the transfer at the new block
			let alice_balance_after = blockchain
				.storage_at(new_block.number, &alice_key)
				.await
				.expect("Failed to get Alice balance after")
				.map(|v| decode_free_balance(&v))
				.expect("Alice should still have a balance");

			let bob_balance_after = blockchain
				.storage_at(new_block.number, &bob_key)
				.await
				.expect("Failed to get Bob balance after")
				.map(|v| decode_free_balance(&v))
				.expect("Bob should still have a balance");

			// Verify the transfer happened
			// Alice's balance should decrease (transfer amount + fees)
			assert!(
				alice_balance_after < alice_balance_before,
				"Alice balance should decrease after transfer"
			);
			// Bob should receive exactly the transfer amount
			assert_eq!(
				bob_balance_after,
				bob_balance_before + TRANSFER_AMOUNT,
				"Bob should receive exactly the transfer amount"
			);
			// Alice should have paid at least the transfer amount (plus fees)
			assert!(
				alice_balance_before - alice_balance_after >= TRANSFER_AMOUNT,
				"Alice should have paid at least the transfer amount plus fees"
			);
		}

		#[tokio::test(flavor = "multi_thread")]
		async fn block_body_returns_extrinsics_for_head() {
			let ctx = TestContext::minimal().await;

			let blockchain =
				Blockchain::fork(&ctx.endpoint, None).await.expect("Failed to fork blockchain");

			// Build a block so we have extrinsics (inherents)
			let block = blockchain.build_empty_block().await.expect("Failed to build block");

			// Query body for head hash
			let body = blockchain.block_body(block.hash).await.expect("Failed to get block body");

			assert!(body.is_some(), "Should return body for head hash");
			// Should have inherent extrinsics
			let extrinsics = body.unwrap();
			assert!(!extrinsics.is_empty(), "Built block should have inherent extrinsics");
		}

		#[tokio::test(flavor = "multi_thread")]
		async fn block_body_returns_extrinsics_for_parent_block() {
			let ctx = TestContext::minimal().await;

			let blockchain =
				Blockchain::fork(&ctx.endpoint, None).await.expect("Failed to fork blockchain");

			// Build two blocks
			let block1 = blockchain.build_empty_block().await.expect("Failed to build block 1");
			let _block2 = blockchain.build_empty_block().await.expect("Failed to build block 2");

			// Query body for the first built block (parent of head)
			let body = blockchain.block_body(block1.hash).await.expect("Failed to get block body");

			assert!(body.is_some(), "Should return body for parent block");
			let extrinsics = body.unwrap();
			assert!(!extrinsics.is_empty(), "Parent block should have inherent extrinsics");
		}

		#[tokio::test(flavor = "multi_thread")]
		async fn block_body_returns_extrinsics_for_fork_point_from_remote() {
			let ctx = TestContext::minimal().await;

			let blockchain =
				Blockchain::fork(&ctx.endpoint, None).await.expect("Failed to fork blockchain");

			let fork_point_hash = blockchain.fork_point();

			// Query body for fork point (should fetch from remote)
			let body =
				blockchain.block_body(fork_point_hash).await.expect("Failed to get block body");

			// Fork point exists on remote chain, so body should be Some
			assert!(body.is_some(), "Should return body for fork point from remote");
			assert!(!body.unwrap().is_empty(), "Should contain body");
		}

		#[tokio::test(flavor = "multi_thread")]
		async fn block_body_returns_none_for_unknown_hash() {
			let ctx = TestContext::minimal().await;

			let blockchain =
				Blockchain::fork(&ctx.endpoint, None).await.expect("Failed to fork blockchain");

			// Use a fabricated hash that doesn't exist
			let unknown_hash = H256::from([0xde; 32]);

			let body =
				blockchain.block_body(unknown_hash).await.expect("Failed to query block body");

			assert!(body.is_none(), "Should return None for unknown hash");
		}

		#[tokio::test(flavor = "multi_thread")]
		async fn block_header_returns_header_for_head() {
			let ctx = TestContext::minimal().await;

			let blockchain =
				Blockchain::fork(&ctx.endpoint, None).await.expect("Failed to fork blockchain");

			// Build a block so we have a locally-built header
			let block = blockchain.build_empty_block().await.expect("Failed to build block");

			// Query header for head hash
			let header =
				blockchain.block_header(block.hash).await.expect("Failed to get block header");

			assert!(header.is_some(), "Should return header for head hash");
			// Header should not be empty
			let header_bytes = header.unwrap();
			assert!(!header_bytes.is_empty(), "Built block should have a header");
		}

		#[tokio::test(flavor = "multi_thread")]
		async fn block_header_returns_header_for_different_blocks() {
			let ctx = TestContext::minimal().await;

			let blockchain =
				Blockchain::fork(&ctx.endpoint, None).await.expect("Failed to fork blockchain");

			// Build two blocks
			let block1 = blockchain.build_empty_block().await.expect("Failed to build block 1");
			let block2 = blockchain.build_empty_block().await.expect("Failed to build block 2");

			let header_1 = blockchain
				.block_header(block1.hash)
				.await
				.expect("Failed to get block header")
				.unwrap();
			let header_2 = blockchain
				.block_header(block2.hash)
				.await
				.expect("Failed to get block header")
				.unwrap();

			assert_ne!(header_1, header_2);
		}

		#[tokio::test(flavor = "multi_thread")]
		async fn block_header_returns_header_for_fork_point() {
			let ctx = TestContext::minimal().await;

			let blockchain =
				Blockchain::fork(&ctx.endpoint, None).await.expect("Failed to fork blockchain");

			let fork_point_hash = blockchain.fork_point();

			// Query header for fork point (should fetch from remote)
			let header = blockchain
				.block_header(fork_point_hash)
				.await
				.expect("Failed to get block header");

			// Fork point exists on remote chain, so header should be Some
			assert!(header.is_some(), "Should return header for fork point from remote");
			assert!(!header.unwrap().is_empty(), "Should contain header");
		}

		#[tokio::test(flavor = "multi_thread")]
		async fn block_header_returns_none_for_unknown_hash() {
			let ctx = TestContext::minimal().await;

			let blockchain =
				Blockchain::fork(&ctx.endpoint, None).await.expect("Failed to fork blockchain");

			// Use a fabricated hash that doesn't exist
			let unknown_hash = H256::from([0xde; 32]);

			let header = blockchain
				.block_header(unknown_hash)
				.await
				.expect("Failed to query block header");

			assert!(header.is_none(), "Should return None for unknown hash");
		}

		#[tokio::test(flavor = "multi_thread")]
		async fn block_header_returns_header_for_historical_block() {
			let ctx = TestContext::minimal().await;

			let blockchain =
				Blockchain::fork(&ctx.endpoint, None).await.expect("Failed to fork blockchain");

			let fork_number = blockchain.fork_point_number();

			// Only test if fork point is > 0 (has blocks before it)
			if fork_number > 0 {
				// Get the hash of a block before the fork point
				let historical_hash = blockchain
					.block_hash_at(fork_number - 1)
					.await
					.expect("Failed to get historical hash")
					.expect("Historical block should exist");

				// Query header for historical block (before fork point, on remote chain)
				let header = blockchain
					.block_header(historical_hash)
					.await
					.expect("Failed to get block header");

				assert!(header.is_some(), "Should return header for historical block");
				assert!(!header.unwrap().is_empty(), "Historical block should have a header");
			}
		}

		#[tokio::test(flavor = "multi_thread")]
		async fn block_hash_at_returns_hash_for_head() {
			let ctx = TestContext::minimal().await;

			let blockchain =
				Blockchain::fork(&ctx.endpoint, None).await.expect("Failed to fork blockchain");

			// Build a block
			let block = blockchain.build_empty_block().await.expect("Failed to build block");

			// Query hash for head block number
			let hash =
				blockchain.block_hash_at(block.number).await.expect("Failed to get block hash");

			assert!(hash.is_some(), "Should return hash for head block number");
			assert_eq!(hash.unwrap(), block.hash, "Hash should match head block hash");
		}

		#[tokio::test(flavor = "multi_thread")]
		async fn block_hash_at_returns_hash_for_parent_block() {
			let ctx = TestContext::minimal().await;

			let blockchain =
				Blockchain::fork(&ctx.endpoint, None).await.expect("Failed to fork blockchain");

			// Build two blocks
			let block1 = blockchain.build_empty_block().await.expect("Failed to build block 1");
			let _block2 = blockchain.build_empty_block().await.expect("Failed to build block 2");

			// Query hash for the first built block
			let hash =
				blockchain.block_hash_at(block1.number).await.expect("Failed to get block hash");

			assert!(hash.is_some(), "Should return hash for parent block number");
			assert_eq!(hash.unwrap(), block1.hash, "Hash should match first block hash");
		}

		#[tokio::test(flavor = "multi_thread")]
		async fn block_hash_at_returns_hash_for_fork_point() {
			let ctx = TestContext::minimal().await;

			let blockchain =
				Blockchain::fork(&ctx.endpoint, None).await.expect("Failed to fork blockchain");

			let fork_point_number = blockchain.fork_point_number();
			let fork_point_hash = blockchain.fork_point();

			// Query hash for fork point
			let hash = blockchain
				.block_hash_at(fork_point_number)
				.await
				.expect("Failed to get block hash");

			assert!(hash.is_some(), "Should return hash for fork point");
			assert_eq!(hash.unwrap(), fork_point_hash, "Hash should match fork point hash");
		}

		#[tokio::test(flavor = "multi_thread")]
		async fn block_hash_at_returns_hash_for_block_before_fork_point() {
			let ctx = TestContext::minimal().await;

			let blockchain =
				Blockchain::fork(&ctx.endpoint, None).await.expect("Failed to fork blockchain");

			let fork_point_number = blockchain.fork_point_number();

			// Only test if fork point is > 0 (has blocks before it)
			if fork_point_number > 0 {
				let hash = blockchain
					.block_hash_at(fork_point_number - 1)
					.await
					.expect("Failed to get block hash");

				assert!(hash.is_some(), "Should return hash for block before fork point");
			}
		}

		#[tokio::test(flavor = "multi_thread")]
		async fn block_hash_at_returns_none_for_future_block() {
			let ctx = TestContext::minimal().await;

			let blockchain =
				Blockchain::fork(&ctx.endpoint, None).await.expect("Failed to fork blockchain");

			let head_number = blockchain.head_number().await;

			// Query a block number that doesn't exist yet
			let hash = blockchain
				.block_hash_at(head_number + 100)
				.await
				.expect("Failed to query block hash");

			assert!(hash.is_none(), "Should return None for future block number");
		}

		#[tokio::test(flavor = "multi_thread")]
		async fn block_number_by_hash_returns_number_for_head() {
			let ctx = TestContext::minimal().await;

			let blockchain =
				Blockchain::fork(&ctx.endpoint, None).await.expect("Failed to fork blockchain");

			// Build a block
			let block = blockchain.build_empty_block().await.unwrap();

			// Query number by hash
			let number = blockchain
				.block_number_by_hash(block.hash)
				.await
				.expect("Failed to query block number");

			assert_eq!(number, Some(block.number));
		}

		#[tokio::test(flavor = "multi_thread")]
		async fn block_number_by_hash_returns_number_for_parent() {
			let ctx = TestContext::minimal().await;

			let blockchain =
				Blockchain::fork(&ctx.endpoint, None).await.expect("Failed to fork blockchain");

			// Build two blocks
			let block1 = blockchain.build_empty_block().await.unwrap();
			let _block2 = blockchain.build_empty_block().await.unwrap();

			// Query number for first block
			let number = blockchain
				.block_number_by_hash(block1.hash)
				.await
				.expect("Failed to query block number");

			assert_eq!(number, Some(block1.number));
		}

		#[tokio::test(flavor = "multi_thread")]
		async fn block_number_by_hash_returns_number_for_fork_point() {
			let ctx = TestContext::minimal().await;

			let blockchain =
				Blockchain::fork(&ctx.endpoint, None).await.expect("Failed to fork blockchain");

			let fork_hash = blockchain.fork_point();
			let fork_number = blockchain.fork_point_number();

			let number = blockchain
				.block_number_by_hash(fork_hash)
				.await
				.expect("Failed to query block number");

			assert_eq!(number, Some(fork_number));
		}

		#[tokio::test(flavor = "multi_thread")]
		async fn block_number_by_hash_returns_none_for_unknown() {
			let ctx = TestContext::minimal().await;

			let blockchain =
				Blockchain::fork(&ctx.endpoint, None).await.expect("Failed to fork blockchain");

			let unknown_hash = H256::from_slice(&[0u8; 32]);
			let number = blockchain
				.block_number_by_hash(unknown_hash)
				.await
				.expect("Failed to query block number");

			assert!(number.is_none());
		}

		#[tokio::test(flavor = "multi_thread")]
		async fn block_number_by_hash_returns_number_for_historical_block() {
			let ctx = TestContext::minimal().await;

			let blockchain =
				Blockchain::fork(&ctx.endpoint, None).await.expect("Failed to fork blockchain");

			// Get a block before the fork point (if available)
			let fork_number = blockchain.fork_point_number();
			if fork_number > 0 {
				let historical_hash = blockchain
					.block_hash_at(fork_number - 1)
					.await
					.expect("Failed to query block hash")
					.expect("Block should exist");

				let number = blockchain
					.block_number_by_hash(historical_hash)
					.await
					.expect("Failed to query block number");

				assert_eq!(number, Some(fork_number - 1));
			}
		}

		#[tokio::test(flavor = "multi_thread")]
		async fn call_at_block_executes_at_head() {
			let ctx = TestContext::minimal().await;

			let blockchain =
				Blockchain::fork(&ctx.endpoint, None).await.expect("Failed to fork blockchain");

			blockchain.build_empty_block().await.unwrap();
			blockchain.build_empty_block().await.unwrap();
			blockchain.build_empty_block().await.unwrap();

			let head_hash = blockchain.head_hash().await;

			// Call Core_version at head hash
			let result = blockchain
				.call_at_block(head_hash, "Core_version", &[])
				.await
				.expect("Failed to call runtime API");

			assert!(result.is_some(), "Should return result for head hash");
			assert!(!result.unwrap().is_empty(), "Result should not be empty");
		}

		#[tokio::test(flavor = "multi_thread")]
		async fn call_at_block_executes_at_fork_point() {
			let ctx = TestContext::minimal().await;

			let blockchain =
				Blockchain::fork(&ctx.endpoint, None).await.expect("Failed to fork blockchain");

			blockchain.build_empty_block().await.unwrap();
			blockchain.build_empty_block().await.unwrap();
			blockchain.build_empty_block().await.unwrap();

			let fork_hash = blockchain.fork_point();

			// Call Core_version at fork point
			let result = blockchain
				.call_at_block(fork_hash, "Core_version", &[])
				.await
				.expect("Failed to call runtime API");

			assert!(result.is_some(), "Should return result for fork point hash");
			assert!(!result.unwrap().is_empty(), "Result should not be empty");
		}

		#[tokio::test(flavor = "multi_thread")]
		async fn call_at_block_executes_at_parent_block() {
			let ctx = TestContext::minimal().await;

			let blockchain =
				Blockchain::fork(&ctx.endpoint, None).await.expect("Failed to fork blockchain");

			// Build two blocks
			let block1 = blockchain.build_empty_block().await.expect("Failed to build block 1");
			let _block2 = blockchain.build_empty_block().await.expect("Failed to build block 2");

			// Call at the first built block (parent of head)
			let result = blockchain
				.call_at_block(block1.hash, "Core_version", &[])
				.await
				.expect("Failed to call runtime API");

			assert!(result.is_some(), "Should return result for parent block hash");
			assert!(!result.unwrap().is_empty(), "Result should not be empty");
		}

		#[tokio::test(flavor = "multi_thread")]
		async fn call_at_block_returns_none_for_unknown_hash() {
			let ctx = TestContext::minimal().await;

			let blockchain =
				Blockchain::fork(&ctx.endpoint, None).await.expect("Failed to fork blockchain");

			// Use a fabricated hash that doesn't exist
			let unknown_hash = H256::from([0xde; 32]);

			let result = blockchain
				.call_at_block(unknown_hash, "Core_version", &[])
				.await
				.expect("Failed to query");

			assert!(result.is_none(), "Should return None for unknown hash");
		}

		#[tokio::test(flavor = "multi_thread")]
		async fn call_at_block_executes_at_historical_block() {
			let ctx = TestContext::minimal().await;

			let blockchain =
				Blockchain::fork(&ctx.endpoint, None).await.expect("Failed to fork blockchain");

			let fork_number = blockchain.fork_point_number();

			// Only test if fork point is > 0 (has blocks before it)
			if fork_number > 0 {
				// Get the hash of a block before the fork point
				let historical_hash = blockchain
					.block_hash_at(fork_number - 1)
					.await
					.expect("Failed to get historical hash")
					.expect("Historical block should exist");

				// Call at historical block (before fork point, on remote chain)
				let result = blockchain
					.call_at_block(historical_hash, "Core_version", &[])
					.await
					.expect("Failed to call runtime API");

				assert!(result.is_some(), "Should return result for historical block");
				assert!(!result.unwrap().is_empty(), "Result should not be empty");
			}
		}

		/// Verifies that calling `Core_initialize_block` via `call_at_block` does NOT
		/// persist storage changes.
		///
		/// `Core_initialize_block` writes to `System::Number` and other storage keys during
		/// block initialization. This test verifies those changes are discarded after the call.
		#[tokio::test(flavor = "multi_thread")]
		async fn call_at_block_does_not_persist_storage() {
			use crate::{DigestItem, consensus_engine, create_next_header};

			let ctx = TestContext::minimal().await;

			let blockchain =
				Blockchain::fork(&ctx.endpoint, None).await.expect("Failed to fork blockchain");

			// Get head block info
			let head = blockchain.head().await;
			let head_hash = head.hash;
			let head_number = head.number;

			// System::Number storage key = twox128("System") ++ twox128("Number")
			let system_number_key: Vec<u8> =
				[sp_core::twox_128(b"System").as_slice(), sp_core::twox_128(b"Number").as_slice()]
					.concat();

			// Query System::Number BEFORE
			let number_before = blockchain
				.storage(&system_number_key)
				.await
				.expect("Failed to get System::Number")
				.map(|v| {
					u32::from_le_bytes(v.try_into().expect("System::Number should be 4 bytes"))
				})
				.expect("System::Number should exist");

			// Build header for the next block using the crate's helper
			let header = create_next_header(
				&head,
				vec![DigestItem::PreRuntime(consensus_engine::AURA, 0u64.to_le_bytes().to_vec())],
			);

			// Call Core_initialize_block - this WOULD write System::Number = head_number + 1
			let result = blockchain
				.call_at_block(head_hash, "Core_initialize_block", &header)
				.await
				.expect("Core_initialize_block call failed");
			assert!(result.is_some(), "Block should exist");

			// Query System::Number AFTER - should be UNCHANGED
			let number_after = blockchain
				.storage(&system_number_key)
				.await
				.expect("Failed to get System::Number after")
				.map(|v| {
					u32::from_le_bytes(v.try_into().expect("System::Number should be 4 bytes"))
				})
				.expect("System::Number should still exist");

			assert_eq!(
				number_before,
				number_after,
				"System::Number should NOT be modified by call_at_block. \
				 Before: {}, After: {} (would have been {} if persisted)",
				number_before,
				number_after,
				head_number + 1
			);
		}

		#[tokio::test(flavor = "multi_thread")]
		async fn validate_extrinsic_accepts_valid_transfer() {
			use crate::{ExecutorConfig, SignatureMockMode};
			use scale::{Compact, Encode};

			let ctx = TestContext::minimal().await;
			let config = ExecutorConfig {
				signature_mock: SignatureMockMode::AlwaysValid,
				..Default::default()
			};
			let blockchain = Blockchain::fork_with_config(&ctx.endpoint, None, None, config)
				.await
				.expect("Failed to fork blockchain");

			// Build a valid transfer extrinsic
			let head = blockchain.head().await;
			let metadata = head.metadata().await.expect("Failed to get metadata");

			let balances_pallet = metadata.pallet_by_name("Balances").expect("Balances pallet");
			let pallet_index = balances_pallet.index();
			let transfer_call = balances_pallet
				.call_variant_by_name("transfer_keep_alive")
				.expect("transfer_keep_alive");
			let call_index = transfer_call.index;

			let mut call_data = vec![pallet_index, call_index];
			call_data.push(0x00); // MultiAddress::Id
			call_data.extend(BOB);
			call_data.extend(Compact(TRANSFER_AMOUNT).encode());

			let extrinsic = build_mock_signed_extrinsic_v4(&call_data);

			// Validate should succeed
			let result = blockchain.validate_extrinsic(&extrinsic).await;
			assert!(result.is_ok(), "Valid extrinsic should pass validation: {:?}", result);
		}

		#[tokio::test(flavor = "multi_thread")]
		async fn validate_extrinsic_rejects_garbage() {
			let ctx = TestContext::minimal().await;
			let blockchain =
				Blockchain::fork(&ctx.endpoint, None).await.expect("Failed to fork blockchain");

			// Submit garbage bytes
			let garbage = vec![0xde, 0xad, 0xbe, 0xef];

			let result = blockchain.validate_extrinsic(&garbage).await;
			assert!(result.is_err(), "Garbage should fail validation");
		}

		#[tokio::test(flavor = "multi_thread")]
		async fn build_block_result_tracks_included_extrinsics() {
			use crate::{ExecutorConfig, SignatureMockMode};
			use scale::{Compact, Encode};

			let ctx = TestContext::minimal().await;
			let config = ExecutorConfig {
				signature_mock: SignatureMockMode::AlwaysValid,
				..Default::default()
			};
			let blockchain = Blockchain::fork_with_config(&ctx.endpoint, None, None, config)
				.await
				.expect("Failed to fork");

			// Build a valid transfer extrinsic
			let head = blockchain.head().await;
			let metadata = head.metadata().await.expect("Failed to get metadata");

			let balances_pallet = metadata.pallet_by_name("Balances").expect("Balances pallet");
			let pallet_index = balances_pallet.index();
			let transfer_call = balances_pallet
				.call_variant_by_name("transfer_keep_alive")
				.expect("transfer_keep_alive");
			let call_index = transfer_call.index;

			let mut call_data = vec![pallet_index, call_index];
			call_data.push(0x00); // MultiAddress::Id
			call_data.extend(BOB);
			call_data.extend(Compact(TRANSFER_AMOUNT).encode());

			let extrinsic = build_mock_signed_extrinsic_v4(&call_data);

			let result = blockchain
				.build_block(vec![extrinsic.clone()])
				.await
				.expect("Failed to build block");

			assert_eq!(result.included.len(), 1, "Should have 1 included extrinsic");
			assert!(result.failed.is_empty(), "Should have no failed extrinsics");
			assert_eq!(result.included[0], extrinsic);
		}

		#[tokio::test(flavor = "multi_thread")]
		async fn build_block_result_tracks_failed_extrinsics() {
			use crate::{ExecutorConfig, SignatureMockMode};
			use scale::{Compact, Encode};

			let ctx = TestContext::minimal().await;
			let config = ExecutorConfig {
				signature_mock: SignatureMockMode::AlwaysValid,
				..Default::default()
			};
			let blockchain = Blockchain::fork_with_config(&ctx.endpoint, None, None, config)
				.await
				.expect("Failed to fork");

			// Build an extrinsic that will fail at dispatch time - transfer more than available.
			// Use a random account with no funds to trigger InsufficientBalance.
			let head = blockchain.head().await;
			let metadata = head.metadata().await.expect("Failed to get metadata");

			let balances_pallet = metadata.pallet_by_name("Balances").expect("Balances pallet");
			let pallet_index = balances_pallet.index();
			let transfer_call = balances_pallet
				.call_variant_by_name("transfer_keep_alive")
				.expect("transfer_keep_alive");
			let call_index = transfer_call.index;

			// Use a "random" account that has no funds as the sender.
			// The extrinsic is structurally valid but will fail dispatch due to lack of funds.
			let unfunded_account: [u8; 32] = [0x99; 32];
			let recipient = BOB;
			let amount: u128 = 1_000_000_000_000_000; // Large amount that unfunded account can't pay

			let mut call_data = vec![pallet_index, call_index];
			call_data.push(0x00); // MultiAddress::Id
			call_data.extend(recipient);
			call_data.extend(Compact(amount).encode());

			// Build extrinsic from unfunded account
			let extrinsic = {
				let mut inner = Vec::new();
				inner.push(0x84); // Version: signed (0x80) + v4 (0x04)
				inner.push(0x00); // MultiAddress::Id variant
				inner.extend(unfunded_account);
				inner.extend([0u8; 64]); // Dummy signature (works with AlwaysValid)
				inner.push(0x00); // CheckMortality: immortal
				inner.extend(Compact(0u64).encode()); // CheckNonce
				inner.extend(Compact(0u128).encode()); // ChargeTransactionPayment
				inner.push(0x00); // EthSetOrigin: None
				inner.extend(&call_data);
				let mut final_ext = Compact(inner.len() as u32).encode();
				final_ext.extend(inner);
				final_ext
			};

			let result = blockchain
				.build_block(vec![extrinsic.clone()])
				.await
				.expect("Build should succeed even with failed extrinsics");

			// The extrinsic should fail at dispatch (InsufficientBalance) and be in the failed list
			assert!(
				result.failed.len() == 1,
				"Failed extrinsic should be tracked. Included: {}, Failed: {}",
				result.included.len(),
				result.failed.len()
			);
			assert!(result.included.is_empty(), "Failed extrinsic should not be in included list");
			assert_eq!(result.failed[0].extrinsic, extrinsic);
		}
	}

	#[test]
	fn transaction_validity_error_reason_returns_correct_strings() {
		let stale = TransactionValidityError::Invalid(InvalidTransaction::Stale);
		assert_eq!(stale.reason(), "Nonce too low (already used)");

		let payment = TransactionValidityError::Invalid(InvalidTransaction::Payment);
		assert_eq!(payment.reason(), "Insufficient funds for fees");

		let unknown = TransactionValidityError::Unknown(UnknownTransaction::CannotLookup);
		assert_eq!(unknown.reason(), "Cannot lookup validity");
	}

	#[test]
	fn transaction_validity_error_is_unknown_distinguishes_types() {
		let invalid = TransactionValidityError::Invalid(InvalidTransaction::Stale);
		assert!(!invalid.is_unknown());

		let unknown = TransactionValidityError::Unknown(UnknownTransaction::CannotLookup);
		assert!(unknown.is_unknown());
	}

	#[test]
	fn transaction_validity_types_can_be_decoded() {
		use scale::Decode;

		// Valid transaction result (index 0)
		let valid_bytes = [
			0x00, // Ok variant
			0x01, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, // priority: 1
			0x00, // requires: empty vec
			0x00, // provides: empty vec
			0x40, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, // longevity: 64
			0x01, // propagate: true
		];
		let validity = TransactionValidity::decode(&mut valid_bytes.as_slice())
			.expect("Should decode valid transaction");
		match validity {
			TransactionValidity::Ok(valid) => {
				assert_eq!(valid.priority, 1);
				assert!(valid.requires.is_empty());
				assert!(valid.provides.is_empty());
				assert_eq!(valid.longevity, 64);
				assert!(valid.propagate);
			},
			TransactionValidity::Err(_) => panic!("Expected Ok variant"),
		}

		// Invalid transaction result (index 1) with Stale (index 3)
		let invalid_bytes = [
			0x01, // Err variant
			0x00, // Invalid variant
			0x03, // Stale
		];
		let validity = TransactionValidity::decode(&mut invalid_bytes.as_slice())
			.expect("Should decode invalid transaction");
		match validity {
			TransactionValidity::Ok(_) => panic!("Expected Err variant"),
			TransactionValidity::Err(err) => {
				assert_eq!(err.reason(), "Nonce too low (already used)");
			},
		}
	}
}