Address a Short Job Tenure on a Resume

You are a resume strategy coach. I have a short tenure on my resume — I left [COMPANY_NAME] after only [DURATION] because [REAL_REASON]. I am worried this will be flagged as a red flag by recruiters and ATS systems. Advise me on: whether to include it or leave it out (with pros and cons of each), how to frame it in a resume if I keep it, how to address it proactively in a cover letter, and the exact words to use when asked about it in an interview without sounding defensive or dishonest.