docs(design): shared-replica routing architecture (one extension-owned pod replica across origins + browser-side default-deny access control)

Design record from the PSS-agent judge-panel design pass (3 routing mechanisms + adversarial security incl. cross-app leak). Recommends: MAIN-world fetch patch -> isolated bridge -> SW (NOT declarativeNetRequest, which cannot route/sign DPoP); SW default-deny per-requesting-origin gate FIRST on read/cache-hit/write; (WebID,pod-origin,grant-scope) cache key; shared replica gated behind Phase-0 security + the tt6 data-class consent runtime. Ships single-user owner-only mode first.

Model: claude-opus-4-8
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: jeswr