Extends the realtime session protocol with tool.call/tool.result/response.trigger
so the model can invoke functions that run either on our server or, relayed
through the session, in the browser (e.g. DOM interaction) — a single
outstanding-call counter lets a turn mix both without racing the model's
continuation. createToolRegistry enforces at startup that a client-only tool
can never accidentally be backed by server logic.
Also introduces a project/ namespace alongside core/, server/core/, and
client/core/, for code specific to whichever client project branches from
this template. Core never imports project; the two composition roots
(server.js, vite.config.ts) do the merge instead, so template updates can
still be pulled into a branched project without touching core files.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>