Forge a writer-ready brief from an article suggestion. `channel` picks the brief template: article (default, SEO article outline), reels (hook/beats/shot list), youtube (retention beats/chapters), x (thread posts), linkedin (carousel slide deck: cover hook, one-idea slides, recap, CTA). A suggestion holds one brief per channel — generating a second channel adds a brief without touching the others. When the suggestion already has an article brief, channel briefs DERIVE from it (its key points, hook, and keyStats flow into the channel shape) and are free — they do not consume a daily brief slot. Idempotent per channel: if that channel already has a brief, returns it without consuming a slot; pass `force: true` to regenerate it. When regenerating, pass `guidance` — corrective direction the forge must follow (e.g. the angle the operator actually wants, a section to drop, an audience correction) — instead of re-rolling blind and hoping. Free tier: 10/day for article briefs and non-derived channel briefs. Returns `{ entitlement }` when the daily cap is reached.