Call the attachImageToPost MCP tool

Attach an image to a draft, planned, or approved post; refuses scheduled or published posts. If the post already has an image, this points it at the NEW one instead, it does not delete the previous upload (the old file becomes an orphaned storage object, not removed). Provide exactly one of image_url (fetched server-side, https only, up to 5 MB decoded), image_base64 (the base64 text is capped at 2 MB, which is roughly 1.5 MB of actual image once decoded because base64 inflates size by about 4/3, so use image_url for anything larger), or asset_name (a name from listAssets, loaded straight from storage with no bytes through the model). Every image is also checked against the 5 MB decoded cap. png/jpeg/webp/gif only, detected from the image bytes themselves, never from a Content-Type header.

Called through the Actions bridge: the response is that tool's own result, wrapped as { data: <tool result> } under HTTP 200. Billing, daily-cap, and confirm-step outcomes are embedded INSIDE data, never remapped to an HTTP status (see the templated /api/v1/actions/{toolName} operation above for the full protocol, and x-mcp-actions for this tool's machine-readable scope/cap/confirm_behavior fields). Authentication, request-shape, and optional idempotency-protocol failures still use their documented non-200 statuses.