feat(engine): respond unsupported for payload v5 pre-osaka (#16268)

Author: rkrasiuk

crates/payload/primitives/src/lib.rs

@@ -133,6 +133,19 @@ pub fn validate_payload_timestamp(
         //    the payload does not fall within the time frame of the Prague fork.
         return Err(EngineObjectValidationError::UnsupportedFork)
     }
+
+    let is_osaka = chain_spec.is_osaka_active_at_timestamp(timestamp);
+    if version.is_v5() && !is_osaka {
+        // From the Engine API spec:
+        // <https://github.com/ethereum/execution-apis/blob/15399c2e2f16a5f800bf3f285640357e2c245ad9/src/engine/osaka.md#specification>
+        //
+        // For `engine_getPayloadV5`
+        //
+        // 1. Client software MUST return -38005: Unsupported fork error if the timestamp of the
+        //    built payload does not fall within the time frame of the Osaka fork.
+        return Err(EngineObjectValidationError::UnsupportedFork)
+    }
+
     Ok(())
 }