feat(tests): EIP-7918 - Blob base fee bounded by execution cost (#1685)

* feat(forks|tests): eip-7918 initial tests plus eip-4844 adjustments.

* chore(tests): extra param and docstring tweak.

Author: spencer-tb

ethereum_test_forks/base_fork.py

@@ -96,6 +96,7 @@ def __call__(
         parent_excess_blobs: int | None = None,
         parent_blob_gas_used: int | None = None,
         parent_blob_count: int | None = None,
+        parent_base_fee_per_gas: int,
     ) -> int:
         """Return the excess blob gas given the parent's excess blob gas and blob gas used."""
         pass

ethereum_test_forks/forks/forks.py

@@ -960,6 +960,7 @@ def fn(
             parent_excess_blobs: int | None = None,
             parent_blob_gas_used: int | None = None,
             parent_blob_count: int | None = None,
+            parent_base_fee_per_gas: int,  # Required for Osaka as using this as base
         ) -> int:
             if parent_excess_blob_gas is None:
                 assert parent_excess_blobs is not None, "Parent excess blobs are required"
@@ -1388,6 +1389,55 @@ def precompiles(cls, block_number: int = 0, timestamp: int = 0) -> List[Address]
         """
         return [Address(0x100)] + super(Osaka, cls).precompiles(block_number, timestamp)
 
+    @classmethod
+    def excess_blob_gas_calculator(
+        cls, block_number: int = 0, timestamp: int = 0
+    ) -> ExcessBlobGasCalculator:
+        """Return a callable that calculates the excess blob gas for a block."""
+        target_blobs_per_block = cls.target_blobs_per_block(block_number, timestamp)
+        blob_gas_per_blob = cls.blob_gas_per_blob(block_number, timestamp)
+        target_blob_gas_per_block = target_blobs_per_block * blob_gas_per_blob
+        max_blobs_per_block = cls.max_blobs_per_block(block_number, timestamp)
+        blob_base_cost = 2**14  # EIP-7918 new parameter
+
+        def fn(
+            *,
+            parent_excess_blob_gas: int | None = None,
+            parent_excess_blobs: int | None = None,
+            parent_blob_gas_used: int | None = None,
+            parent_blob_count: int | None = None,
+            parent_base_fee_per_gas: int,  # EIP-7918 additional parameter
+        ) -> int:
+            if parent_excess_blob_gas is None:
+                assert parent_excess_blobs is not None, "Parent excess blobs are required"
+                parent_excess_blob_gas = parent_excess_blobs * blob_gas_per_blob
+            if parent_blob_gas_used is None:
+                assert parent_blob_count is not None, "Parent blob count is required"
+                parent_blob_gas_used = parent_blob_count * blob_gas_per_blob
+            if parent_excess_blob_gas + parent_blob_gas_used < target_blob_gas_per_block:
+                return 0
+
+            # EIP-7918: Apply reserve price when execution costs dominate blob costs
+            current_blob_base_fee = cls.blob_gas_price_calculator()(
+                excess_blob_gas=parent_excess_blob_gas
+            )
+            reserve_price_active = (
+                blob_base_cost * parent_base_fee_per_gas
+                > blob_gas_per_blob * current_blob_base_fee
+            )
+            if reserve_price_active:
+                blob_excess_adjustment = (
+                    parent_blob_gas_used
+                    * (max_blobs_per_block - target_blobs_per_block)
+                    // max_blobs_per_block
+                )
+                return parent_excess_blob_gas + blob_excess_adjustment
+
+            # Original EIP-4844 calculation
+            return parent_excess_blob_gas + parent_blob_gas_used - target_blob_gas_per_block
+
+        return fn
+
 
 class EOFv1(Prague, solc_name="cancun"):
     """EOF fork."""