Dotfiles Architecture Contract

Load BEFORE proposing any structural or design change to the dotfiles repo, and whenever you catch yourself asking "why is it built this way", "can I just track this file", "why is settings.json not symlinked", "why two config dirs", "why is this untracked", or "can the SessionStart hook install the plugin". Documents the eight load-bearing design decisions with rationale, the invariants that must hold, and the known weak points, plus the install-layout reference (install flow, symlink and seed targets, hook catalogue) and the Codex plugin integration reference (codex-surfaces.py / codex-roles.py reconciliation, staging provenance). NOT for making/committing a change (dot…