AccountID / ExternalID / Error are server-managed publish results, set only by the publish path (never by a client update): the account a post was published through, the provider's returned external post id (for reconciliation), and the last failure reason. Empty until a publish attempt lands. AccountID is the connected account the post went out through. Absent until a publish succeeds.
Channel is the network this post targets: x, facebook, instagram, linkedin, tiktok, youtube or threads. It is the channel whose CONNECTED accounts a publish fans out to. Example: "x"
ExternalID is the id the network returned for the published post, which is what reconciles this row against the post on the network. Absent until a publish succeeds.
Media is the post's attached media as a list of URLs (images today; the composer's URL field now, an S3 picker later, populate it). Stored as a JSON array in the media TEXT column and ALWAYS serialized as an array (never null), so a client can rely on media being present. Bounded at the write layer (normMedia in social.go): each URL clipped to maxField, the list to maxMedia.
ScheduleAt is when the post is due, as a unix timestamp in SECONDS. 0 means unscheduled. It is meaningful only while the status is scheduled — a scheduled post whose time has arrived is published by the scheduler.
Status is the post's lifecycle state: draft, scheduled, published or failed. A fifth, transient publishing state exists while a publish attempt holds the claim; it is never settable from a request and a caller sees it only if it reads a post mid-attempt.
