test(tests): add BLOCKHASH genesis hash availability test (#2228)

* test(tests): add BLOCKHASH genesis hash availability test

Add regression test verifying BLOCKHASH(0) returns genesis hash in block 1.
Tests blockchain test infrastructure properly populates genesis hash before
execution, preventing BLOCKHASH(0) from returning 0.

Regression context: revm blockchaintest runner wasn't inserting block_hashes
into state, causing BLOCKHASH(0) to return 0. This broke tests with dynamic
address computations like BLOCKHASH(0) | TIMESTAMP, where the computed
address would be incorrect, leading to balance transfer failures.

Test validates infrastructure setup by storing ISZERO(BLOCKHASH(0)) which
should be 0 (false) when genesis hash is properly available.

* test(tests): extend BLOCKHASH test to verify block 1 hash availability

Extends test_genesis_hash_available to verify both genesis (block 0)
and first executed block (block 1) hash insertion by adding a second
block that calls the contract, testing BLOCKHASH(0) and BLOCKHASH(1).

Addresses PR feedback to test complete block hash infrastructure.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <[email protected]>

---------

Co-authored-by: Claude <[email protected]>

Author: bshastry

tests/frontier/opcodes/test_blockhash.py

@@ -0,0 +1,74 @@
+"""Tests for BLOCKHASH opcode."""
+
+import pytest
+
+from ethereum_test_tools import (
+    Account,
+    Alloc,
+    Block,
+    BlockchainTestFiller,
+    Storage,
+    Transaction,
+)
+from ethereum_test_tools import Opcodes as Op
+
+
+@pytest.mark.valid_from("Frontier")
+def test_genesis_hash_available(blockchain_test: BlockchainTestFiller, pre: Alloc):
+    """
+    Verify BLOCKHASH returns genesis and block 1 hashes.
+
+    Regression test: Blockchain test infrastructure must populate block hashes
+    before execution. Without this, BLOCKHASH returns 0, breaking dynamic
+    address computations like BLOCKHASH(0) | TIMESTAMP.
+
+    Tests both genesis (block 0) and first executed block (block 1) hash
+    insertion by calling the contract in block 2.
+
+    Bug context: revm blockchaintest runner wasn't inserting block_hashes,
+    causing failures in tests with BLOCKHASH-derived addresses.
+    """
+    storage = Storage()
+
+    # Store ISZERO(BLOCKHASH(0)) and ISZERO(BLOCKHASH(1))
+    # Both should be 0 (false) if hashes exist
+    code = Op.SSTORE(storage.store_next(0), Op.ISZERO(Op.BLOCKHASH(0))) + Op.SSTORE(
+        storage.store_next(0), Op.ISZERO(Op.BLOCKHASH(1))
+    )
+
+    contract = pre.deploy_contract(code=code)
+    sender = pre.fund_eoa()
+
+    blocks = [
+        Block(
+            txs=[
+                Transaction(
+                    sender=sender,
+                    to=contract,
+                    gas_limit=100_000,
+                    protected=False,
+                )
+            ]
+        ),
+        Block(
+            txs=[
+                Transaction(
+                    sender=sender,
+                    to=contract,
+                    gas_limit=100_000,
+                    protected=False,
+                )
+            ]
+        ),
+    ]
+
+    post = {
+        contract: Account(
+            storage={
+                0: 0,  # ISZERO(BLOCKHASH(0)) = 0 (genesis hash exists)
+                1: 0,  # ISZERO(BLOCKHASH(1)) = 0 (block 1 hash exists)
+            }
+        )
+    }
+
+    blockchain_test(pre=pre, post=post, blocks=blocks)