feature: vre opens files from the Router Manager's shell in the editor of its Shell page.

ADR.md

@@ -1230,3 +1230,26 @@ the addresses setup records for the web service.
 Consequences: Clients resolve the listed domains through the tunnel and everything else with their
 own resolvers. Clients that ignore attribute 25 keep the scoped behaviour; the Apple profile
 covers Apple devices. A changed list reaches an Apple device with a newly installed profile.
+
+## ADR-46: vre opens files in the Shell page's editor over a socket checked by the peer's uid
+
+Status: Accepted
+
+Context: Administrators edit the router's files from the Router Manager's Shell page, in an editor
+of the page rather than a terminal editor. The command that names a file runs in the shell, as the
+console account. The web service runs as root, sandboxed with `ProtectHome=yes`, so it cannot see
+the accounts' home folders. Reading and writing as root would also bypass the account's
+permissions.
+
+Decision: Each shell has a random session in `VPN_ROUTER_SHELL`. `vpn-router-editor` (`vre`) sends
+the session and an absolute path to the web service on `/run/vpn-router/editor.sock`, which anyone
+may connect to. The web service accepts a request only when the peer's uid (`SO_PEERCRED`) is the
+uid of the session's console account. It then tells the shell's client over the shell's WebSocket,
+and the page reads and saves the file through `/shell/editor/<session>/<id>`. Files are read and
+written by `editor-file`, run with `systemd-run --uid=<account> --pipe` outside the sandbox, as the
+shell is. A save carries the SHA-256 of the content it replaces and is refused when the file
+changed since. Files open only while their shell lives.
+
+Consequences: The editor edits only what the console account may; a file only root may write is
+edited in the terminal. `vre` run under sudo is refused, as its uid is not the console account's.
+Each read and save starts a transient unit. Files are limited to 1 MiB of UTF-8 text.