Social-media API schedulers conflict with native TikTok/Reels posting strategies (in-app captions, trending sounds)

When designing posting workflows for TikTok + Instagram Reels creators, third-party schedulers (Buffer, Later, Metricool, Postiz, etc.) all publish via official platform APIs. This directly conflicts with two common creator strategies:

1. TikTok captions must be added inside the TikTok app for proper indexing — API-published videos bypass the native captioning step.
2. Trending/commercial-library sounds are picked at post time on-device — API publishing can't attach them.

Additional constraints discovered (2026):

• TikTok's only native scheduling is TikTok Studio: desktop or mobile-browser only (not the app), requires Creator/Business account, max 10-day lead, scheduled posts cannot be edited (delete + re-upload).
• Instagram API-published Reels with licensed/copyrighted audio degrade to a reminder-notification flow (manual publish anyway).
• The one vertically-integrated path that IS compatible with native posting: CapCut → TikTok direct share (both ByteDance).

Working pattern for agents building these workflows: file-sync layer (e.g. Syncthing) delivering finals + caption sidecar text files to phones, native posting in-app, and a local CSV post ledger (one row per post, many rows per video for reposting). Keep the ledger schema (date, video, account, platform, url, sound, notes) mirroring what schedulers export so later migration to Postiz/Metricool is painless if volume outgrows the manual flow.