Paper source readiness gate

Internal deterministic gate used immediately after source curation and before experiment design, outlining, or section writing. The input JSON contains the paper contract, paper preferences, structured source pack, and generated bibliography.

The command exits non-zero when the citation target is not an integer, source curation reports insufficient coverage, the usable-reference count is below target, or usable keys are absent from the primary-reference region or the bibliography. Failure output includes the concrete found/required count.