Math processes on the top-level / multiple save_results in process

Hi,

I have Python client code:

import openeo
from openeo.processes import power

connection = openeo.connect("https://earthengine.openeo.org").authenticate_basic("group2", "test123")

aoi = {
  "type": "Polygon",
  "coordinates": [
    [[-7.664532, 38.543869], [-7.689248, 38.141037], [-7.159228, 38.151837], [-7.11289, 38.554609], [-7.664532, 38.543869]]
  ]
}

EPSG = 32629

data = connection.load_collection(
  collection_id = "COPERNICUS/S2_SR_HARMONIZED",
  spatial_extent = aoi,
  temporal_extent = ["2019-06-27T00:00:00Z", "2019-07-04T00:00:00Z"],
  bands = ["B1", "B2", "B3", "B4"]
)

# If we get multiple images (should not happen for the given extent), compute the mean
# Divide by 10000 to convert from DN to reflectance values
data = data.mean_time() / 10000

# Assign the indivdual bands to variables
B1 = data.band("B1")
B2 = data.band("B2")
B3 = data.band("B3")
B4 = data.band("B4")

# Density of cyanobacteria
cyanobacteria = 115530 * power((B3 * B4) / B2, 2.38)
save1 = cyanobacteria.save_result(
  format = "GTIFF",
  options = {
    "name": "cyanobacteria",
    "metadata": {
      "bands": [ { "statistics": { "minimum": 0, "maximum": 100 } } ]
    },
    "epsgCode": EPSG
  }
)

Unfortunately, I get the following error once I run result1 = connection.execute(save1):

Preflight process graph validation raised: [ProcessArgumentInvalid] The argument 'base' in process 'power' (namespace: n/a) is invalid: Schema for result 'reducedimension2' not compatible

Looking at the generated JSON, this is not overly surprising anymore:

Why does the client put power and multiply on the top-level? It works flawlessly with the divide by 10000 in apply.

Start by reproducing the issue with the Python client code and inspect the generated process graph passed to connection.execute(save1). Compare how power and multiply are placed with the working divide-by-10000 expression and review the process-graph construction around these operations. Done means the generated graph passes preflight validation for the shown expression.