Validate post content
Dry-run exactly the checks create runs, WITHOUT creating anything, so valid: true means create would accept the post: per-platform caption limits (each limit grounded in the platform handler or the platform’s documented maximum, counted the way the platform counts), platform text rules (Instagram hashtags and @mentions, Threads links), required media (Instagram, Pinterest, TikTok), media that suits the post type (an Instagram or Facebook Reel and a YouTube video need a video; an Instagram or Facebook Reel or Story takes exactly one file; a TikTok photo post takes images only), media counts and formats, file types, and the platform’s post fields (e.g. TikTok who can view). Each platform is checked against its own text and media when platform_overrides are sent. Free and unbilled. Platforms with no honestly-documented ceiling (Snapchat stories carry no caption; Tumblr documents no body cap) report limit: null. Requires scope social:read.
Authorizations
API key from Developer dashboard (Bearer token).
Body
Target platforms, e.g. ["twitter", "instagram"].
Post text to check.
Media URLs the post would carry (used for required-media and extension checks).
Optional. Per-platform options as on create (post type, TikTok privacy, ...). The post type decides which media a platform needs.
Optional. Per-platform text and media as on create; each platform is checked against its own.

