Move timestamp validation down to ease validation

src/engine/cancun.md

@@ -94,9 +94,9 @@ Refer to the response for [`engine_newPayloadV2`](./shanghai.md#engine_newpayloa
 
 This method follows the same specification as [`engine_newPayloadV2`](./shanghai.md#engine_newpayloadv2) with the addition of the following:
 
-1. Client software **MUST** return `-38005: Unsupported fork` error if the `timestamp` of the payload does not fall within the time frame of the Cancun fork.
+1. Client software **MUST** check that provided set of parameters and their fields strictly matches the expected one and return `-32602: Invalid params` error if this check fails. Any field having `null` value **MUST** be considered as not provided.
 
-2. Client software **MUST** check that provided set of parameters and their fields strictly matches the expected one and return `-32602: Invalid params` error if this check fails. Any field having `null` value **MUST** be considered as not provided.
+2. Client software **MUST** return `-38005: Unsupported fork` error if the `timestamp` of the payload does not fall within the time frame of the Cancun fork.
 
 3. Given the expected array of blob versioned hashes client software **MUST** run its validation by taking the following steps:
     1. Obtain the actual array by concatenating blob versioned hashes lists (`tx.blob_versioned_hashes`) of each [blob transaction](https://eips.ethereum.org/EIPS/eip-4844#new-transaction-type) included in the payload, respecting the order of inclusion. If the payload has no blob transactions the expected array **MUST** be `[]`.
@@ -122,9 +122,9 @@ Refer to the response for [`engine_forkchoiceUpdatedV2`](./shanghai.md#engine_fo
 
 This method follows the same specification as [`engine_forkchoiceUpdatedV2`](./shanghai.md#engine_forkchoiceupdatedv2) with addition of the following:
 
-1. Client software **MUST** return `-38005: Unsupported fork` error if the `payloadAttributes.timestamp` does not fall within the time frame of the Cancun fork.
+1. Client software **MUST** check that provided set of parameters and their fields strictly matches the expected one and return `-32602: Invalid params` error if this check fails. Any field having `null` value **MUST** be considered as not provided.
 
-2. Client software **MUST** check that provided set of parameters and their fields strictly matches the expected one and return `-32602: Invalid params` error if this check fails. Any field having `null` value **MUST** be considered as not provided.
+2. Client software **MUST** return `-38005: Unsupported fork` error if the `payloadAttributes.timestamp` does not fall within the time frame of the Cancun fork.
 
 ### engine_getPayloadV3
 
@@ -179,6 +179,6 @@ For the following methods:
 - [`engine_newPayloadV2`](./shanghai.md#engine_newpayloadV2)
 - [`engine_getPayloadV2`](./shanghai.md#engine_getpayloadv2)
 
-an early validation **MUST** be added:
+a validation **MUST** be added:
 
 1. Client software **MUST** return `-38005: Unsupported fork` error if the `timestamp` of payload or payloadAttributes greater or equal to the Cancun activation timestamp.