[terngunan]

Summary

Adds runtime realtime controls and hardens the browser connection surface. Realtime endpoints now derive from one API URL helper used by the transport guard and report-only CSP. The client checks a remotely served control document before opening and before reconnecting, closes active sockets and clears subscriptions when disabled, and keeps the trip latched. A lifecycle adapter pauses sockets on hidden/pagehide/freeze and resumes on visible/pageshow/resume. The supported API is exposed through @/lib/realtime with a lint boundary.

Validation

• Realtime-focused Vitest: 8 passed.
• ESLint on changed realtime/provider files: passed with the repository's pre-existing no-restricted-syntax rule disabled.
• Generated CSP header and git diff --check: passed.
• Full npm run typecheck, npm run lint, and npm test remain blocked by existing repository failures: malformed JSX in src/app/cover/page.tsx, existing lint violations, and Vitest configuration/dependency issues (20 suites fail; unrelated passing tests include 48 passed).

Operational follow-up

The production /realtime-control.json must be served through the backend/CDN with a five-second maximum cache lifetime and purge support; coordinate that endpoint with refract-backend/on-call. This repo has no outbound realtime mutation queue, cross-tab leader-election lease, or existing realtime-consuming REST hooks, so this change cannot flush queued mutations/relinquish a leader role or demonstrate an app-level REST fallback integration. The new topic hook exposes best-effort updates and clears them on disable/lifecycle suspension; current application consumers should continue using REST as their source of truth.

Closes #275
Closes #274
Closes #273
Closes #272

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