Soft-delete one file from the library. Never blocked, and that is the trap: a published email_send step still naming this sid keeps the ref (retained: workflow_versions) and fails its send with attachment_missing, sending nothing rather than a partial set. There is no reverse index: the steps naming it turn up only in workflow step documents (attachments[]), so republish those first. Idempotent (repeat returns already_deleted:true); no restore through the API, and re-uploading mints a new sid.

Contract:

• MCP tool delete_workflow_attachment, registry package mcp.playtables/workflow_attachments, mount playtables.workflows.
• Operation delete, response envelope delete_simple.
• Flags: dangerous: the MCP layer gates it behind a preview/commit token, and the effect cannot be undone through this API.