Adding df column finding matching values in another df for both indexed values and a dynamic source column?

Question

Simplified dfs:

df = pd.DataFrame({\'ID\': [6, 2, 4], \'to ignore\': [\'foo\', \'whatever\', \'idk\'], \'value\': [\'A\', \'B\', \'A\']})

df2 = pd.DataFrame(