File Access
Domain: Security & Permissions
Motivation
File access is the question of which files an operation may touch. In dsh, the sandbox mode decides: read-only denies all writes, workspace-write allows writes under the workspace root plus a platform temp area, and danger-full-access bypasses confinement. The fs fence in dsh-fs-sandbox re-canonicalizes the target and checks containment; the observation policy in dsh-fs-observation-policy requires a prior read before an edit. Reads are unrestricted in all modes — the fence governs mutations only.
Concrete Example
Under workspace-write, a read of /etc/hosts succeeds; a write to /etc/hosts is denied with FS_SANDBOX_DENIED; an edit of notes/todo.md succeeds only after a prior read.
Analogy
It is the library: you can browse any book (read), but you can only check out books from your section (workspace-write), and the librarian (observation policy) wants to see your card before you write in a book.