The only mention of Hartest as a possible gildhall is in the SHBG newsletter 'Eavesdropper'' No 17, Autumn 2000 (see Sources) in the article "Angels, Saints, Dragons and Ale" by Patrick Taylor. Of it he said: "Crown Inn (north wing). The Green. The Crown lies immediately west of the church in Hartest and has an interesting jettied north wing that looks like it may have been there first. I understand that Clive Paine has already suggested that this is a parish room or church house and I would agree, a probable." As with others I cannot find any other evidence of a gild or gildhall so this is best regarded as a possible church house until further evidence emerges.
The Historic England listing is here.
The Historic England listing is here.
For information on buildings mentioned in the Pevsner guide to Suffolk in this location see pevsnersuffolk.co.uk