Agent Skills: yjs-nextjs

Corrects the wrong defaults a capable model has when building Yjs collaborative editing into a Next.js 16 App Router app with tRPC v11 and shadcn/ui — pinned to Yjs 13.6.31. Covers the decisions whose failure mode is silence rather than an error — plain objects in a Y.Map discarding concurrent edits, updates that vanish because a JSON boundary turned a Uint8Array into a number array, undo that reverts a colleague's paragraph, initial content seeded once per client, and carets thrown to the end of a shadcn Input on every remote keystroke. Also covers where the sync loop can actually run, since route handlers cannot upgrade, Vercel Functions have no instance affinity, and tRPC subscriptions are one-way — plus which packages have already moved to the Yjs 14 prerelease track. Use when writing, reviewing, or debugging collaborative editing, presence, offline sync, or CRDT persistence in this stack.