todo: security section — privsep + state-file hardening

TODO.md

@@ -26,6 +26,11 @@
 - **Phase 6 follow-ups** — dashboard side is fully event-driven (Phase 6 leftovers landed); the per-agent web UI's lifecycle endpoints (`/api/{cancel,compact,model,new-session}`, `/login/*`) still 303-redirect-and-poll. Convert them to 200 + `data-no-refresh` so the per-agent page stops refetching `/api/state` on every operator click — `LiveEvent::Note` already covers cancel/compact/model/new-session, login state needs its own `NeedsLogin` / `LoggedIn` events on the per-agent bus.
 - **Tombstones + meta_inputs events**: not yet event-derived. PURG3 + meta-update still trigger a post-submit `/api/state` refetch on the dashboard. Add `TombstoneAdded`/`TombstoneRemoved` + `MetaInputsChanged` so those forms can drop their refetch too and the cold-load is the only `/api/state` fetch in normal operation.
 
+## Security
+
+- **Privsep the dashboard from the privileged daemon**: hive-c0re runs as root (it has to — `nixos-container` create / start / destroy, the meta git repo, every per-agent bind mount). The HTTP server lives in the same process, so every read-endpoint (`/api/state-file`, `/api/journal/{name}`, `/api/agent-config/{name}`) is one allow-list bug away from serving arbitrary host files. Split the architecture: keep the privileged daemon doing lifecycle + git + ipc, run the web UI as an unprivileged user that talks to the daemon over a unix socket with a narrow request surface (`ReadAgentStateFile { agent, rel_path }` etc.). The unprivileged process can't read `/etc/shadow` even if every check in `get_state_file` is bypassed — it doesn't have the bits. Container-lifecycle POSTs (`/restart`, `/destroy`, etc.) become forwarded RPCs the privileged side authorises on its terms.
+- **Defense in depth on `get_state_file`**: until privsep lands, the allow-list is load-bearing. Worth adding: refuse files whose mode is not world-readable (so an agent writing a 0600 file inside `state/` can't have its contents proxied through the endpoint to a different operator), and refuse symlinks at any path component (`O_NOFOLLOW`-style — `canonicalize` resolves them, but we currently don't reject if the original path had symlinks).
+
 ## Bugs
 
 - **Post-rebuild system-message missed wake**: at 09:13:14 the dashboard showed `system → damocles container rebuilt` as ✓ delivered, but the agent harness never ran a turn for it (no claude invocation, no operator-visible activity). A subsequent `recv()` from inside the agent returned `(empty)`, confirming the message was popped + marked delivered server-side — yet drove no turn. Most likely cause: the agent_server `serve_agent_stdio` task is up and answering MCP/socket calls, but the `hive-ag3nt::serve` long-poll loop that drives `drive_turn` either died silently during rebuild or never restarted. Investigate: (a) does hive-ag3nt's serve loop survive `nixos-container update` cleanly, or does its tokio runtime get torn down mid-loop? (b) is there an early-exit path on a transient socket error during rebuild that drops the serve task without notifying the manager? (c) compare timeline with manager's own post-rebuild wake to see if this is rebuilt-agents-only or universal. Could be related to the `recv_blocking` fix in `e423d57` if the rebuild restarts the broker mid-subscribe.