feat(nix): container-aware CLI — auto-route into managed container (#7543)

* feat(nix): container-aware CLI — auto-route all subcommands into managed container

When container.enable = true, the host `hermes` CLI transparently execs
every subcommand into the managed Docker/Podman container. A symlink
bridge (~/.hermes -> /var/lib/hermes/.hermes) unifies state between host
and container so sessions, config, and memories are shared.

CLI changes:
- Global routing before subcommand dispatch (all commands forwarded)
- docker exec with -u exec_user, env passthrough (TERM, COLORTERM,
  LANG, LC_ALL), TTY-aware flags
- Retry with spinner on failure (TTY: 5s, non-TTY: 10s silent)
- Hard fail instead of silent fallback
- HERMES_DEV=1 env var bypasses routing for development
- No routing messages (invisible to user)

NixOS module changes:
- container.hostUsers option: lists users who get ~/.hermes symlink
  and automatic hermes group membership
- Activation script creates symlink bridge (with backup of existing
  ~/.hermes dirs), writes exec_user to .container-mode
- Cleanup on disable: removes symlinks + .container-mode + stops service
- Warning when hostUsers set without addToSystemPackages

* fix: address review — reuse sudo var, add chown -h on symlink update

- hermes_cli/main.py: reuse the existing `sudo` variable instead of
  redundant `shutil.which("sudo")` call that could return None
- nix/nixosModules.nix: add missing `chown -h` when updating an
  existing symlink target so ownership stays consistent with the
  fresh-create and backup-replace branches

* fix: address remaining review items from cursor bugbot

- hermes_cli/main.py: move container routing BEFORE parse_args() so
  --help, unrecognised flags, and all subcommands are forwarded
  transparently into the container instead of being intercepted by
  argparse on the host (high severity)

- nix/nixosModules.nix: resolve home dirs via
  config.users.users.${user}.home instead of hardcoding /home/${user},
  supporting users with custom home directories (medium severity)

- nix/nixosModules.nix: gate hostUsers group membership on
  container.enable so setting hostUsers without container mode doesn't
  silently add users to the hermes group (low severity)

* fix: simplify container routing — execvp, no retries, let it crash

- Replace subprocess.run retry loop with os.execvp (no idle parent process)
- Extract _probe_container helper for sudo detection with 15s timeout
- Narrow exception handling: FileNotFoundError only in get_container_exec_info,
  catch TimeoutExpired specifically, remove silent except Exception: pass
- Collapse needs_sudo + sudo into single sudo_path variable
- Simplify NixOS symlink creation from 4 branches to 2
- Gate NixOS sudoers hint with "On NixOS:" prefix
- Full test rewrite: 18 tests covering execvp, sudo probe, timeout, permissions

---------

Co-authored-by: Hermes Agent <hermes@nousresearch.com>

hermes_cli/config.py

@@ -143,6 +143,73 @@ def managed_error(action: str = "modify configuration"):
     print(format_managed_message(action), file=sys.stderr)
 
 
+# =============================================================================
+# Container-aware CLI (NixOS container mode)
+# =============================================================================
+
+def _is_inside_container() -> bool:
+    """Detect if we're already running inside a Docker/Podman container."""
+    # Standard Docker/Podman indicators
+    if os.path.exists("/.dockerenv"):
+        return True
+    # Podman uses /run/.containerenv
+    if os.path.exists("/run/.containerenv"):
+        return True
+    # Check cgroup for container runtime evidence (works for both Docker & Podman)
+    try:
+        with open("/proc/1/cgroup", "r") as f:
+            cgroup = f.read()
+            if "docker" in cgroup or "podman" in cgroup or "/lxc/" in cgroup:
+                return True
+    except OSError:
+        pass
+    return False
+
+
+def get_container_exec_info() -> Optional[dict]:
+    """Read container mode metadata from HERMES_HOME/.container-mode.
+
+    Returns a dict with keys: backend, container_name, exec_user, hermes_bin
+    or None if container mode is not active, we're already inside the
+    container, or HERMES_DEV=1 is set.
+
+    The .container-mode file is written by the NixOS activation script when
+    container.enable = true. It tells the host CLI to exec into the container
+    instead of running locally.
+    """
+    if os.environ.get("HERMES_DEV") == "1":
+        return None
+
+    if _is_inside_container():
+        return None
+
+    container_mode_file = get_hermes_home() / ".container-mode"
+
+    try:
+        info = {}
+        with open(container_mode_file, "r") as f:
+            for line in f:
+                line = line.strip()
+                if "=" in line and not line.startswith("#"):
+                    key, _, value = line.partition("=")
+                    info[key.strip()] = value.strip()
+    except FileNotFoundError:
+        return None
+    # All other exceptions (PermissionError, malformed data, etc.) propagate
+
+    backend = info.get("backend", "docker")
+    container_name = info.get("container_name", "hermes-agent")
+    exec_user = info.get("exec_user", "hermes")
+    hermes_bin = info.get("hermes_bin", "/data/current-package/bin/hermes")
+
+    return {
+        "backend": backend,
+        "container_name": container_name,
+        "exec_user": exec_user,
+        "hermes_bin": hermes_bin,
+    }
+
+
 # =============================================================================
 # Config paths
 # =============================================================================