What changed between two designs, and what it did

Scope: solve. Each side is a design document, { design }, { designId } (a saved design visible to this key) or { templateId } — mix them freely. Both are solved at options.corner (unmetered) and the response lists the document diff (changes), the movement in source power, load power, dissipation, efficiency and warning counts (delta), the converters whose loss moved (stages), every node whose operating point moved (nodes) and the warnings resolved and introduced. Pass options.monteCarlo: { trials, seed } for a yield block — two Monte Carlo runs with the same seed, metered as two runs; 402 QUOTA_EXHAUSTED applies then, and only then. Pro and Team only: a Free account is refused with 403 PLAN_REQUIRED (one sentence and the trial link).