Update posts

Update many posts in one call: explicit edits, or one text replace across matching posts.

Two shapes:

• items: a list of update_post edits, each with its post_id. Applied now, one result per item.
• match + set.caption_replace: "change X to Y in every post that has it". The first call is a dry run: it writes nothing and returns how many posts would change, up to 5 before/after samples, the posts it will skip and a confirm_token. Then send the SAME call with dry_run=false and that confirm_token to apply. Only the matched text changes; status and schedule never do, and published posts are never touched.

Errors: 400 PREVIEW_REQUIRED: A rule apply (dry_run=false) came without a confirm_token. 400 invalid_request: The rule would change more than 200 posts; narrow match.q or match.statuses. 401 authentication_required: API key or token is missing, invalid, or revoked. 403 permission_denied: Your plan does not include API access, or this business is not in your org. 404 resource_not_found: No business with that ID exists. 409 PREVIEW_STALE: Posts changed since the dry run (or it was already applied). Nothing was written. Run the dry run again and apply with its new confirm_token. 422 validation_error: Both or neither of the two shapes, find shorter than 4 characters, or more than 50 items. 429 rate_limit_exceeded: You sent too many requests this minute.