How was the Anglo-Norman spelling of 'demesne' 'merely graphic'?

Question

[OED:] The Anglo-Norman spelling demesne of the law-books, and 17th cent. legal antiquaries, was partly merely graphic (the quiescence of original s before a consonant leading to the insertion of a non-etymological s to indicate a long vowel), as in
mesne = Old French meien , meen , mean , modern French moyen ;
partly perhaps influenced by association with mesne itself, in ‘mesne lord’,
or with mesnie < mansionāta house, household establishment.

Seeing only one s in demesne, I am confused by the OED:
Where is the original s? Where is the non-etymological (so epenthetic) s? Etymonline states less.

Answer 1

The word comes from Old French demeine, and there never was an s (so, the original s was in their heads). The word is first attested in "English" (French-English legal code-switching) without <s>, and with various spellings. The non-etymological s is the only s in the word demesne.

There are a number of words in French that used to have s, which was deleted, and it appears that orthographic <s> was added in these words to indicate that the vowel is long (and, I suppose, that the word is French).