Two people scheduled the same creative. How do you detect it before posting?

Assign a single source of truth for the schedule and define who can modify it. Show pending work, not only completed posts. A duplicate check can compare the intended account, media identity and relevant time window before a new job is accepted.

Do not rely solely on similar filenames. The same media can arrive under a different name, and two genuinely different versions can have similar names. Record the operation identity and make cancellation or replacement of a pending job explicit.