feat(nix): container-aware CLI — auto-route hermes chat into managed container

When container.enable = true in the NixOS module, running 'hermes chat'
on the host now automatically execs into the managed container via
docker/podman exec. This means the interactive CLI runs in the same
environment as the gateway service, with access to all container-installed
packages and tools.

Implementation:
- NixOS activation script writes .container-mode metadata file to
  HERMES_HOME with backend, container_name, and hermes_bin path
- File is removed when container mode is disabled (nixos-rebuild switch)
- hermes_cli/config.py: _is_inside_container() detects Docker/Podman
  indicators (/.dockerenv, /run/.containerenv, cgroup)
- hermes_cli/config.py: get_container_exec_info() reads .container-mode
  metadata, returns None when already inside a container
- hermes_cli/main.py: _exec_in_container() validates the container is
  running, then os.execvp() replaces the process with the container exec
- cmd_chat intercepts before normal flow, checks container info, execs

Safety:
- --host flag bypasses container routing (run on host regardless)
- Falls back to host CLI if: container runtime not found, container not
  running, inspect fails, or any detection error
- Strips --host from forwarded args (not meaningful inside container)
- Already-inside-container detection prevents infinite exec loops

Closes #7380

tests/hermes_cli/test_container_aware_cli.py

@@ -0,0 +1,275 @@
+"""Tests for container-aware CLI routing (NixOS container mode).
+
+When container.enable = true in the NixOS module, the activation script
+writes a .container-mode metadata file. The host CLI detects this and
+execs into the container instead of running locally.
+"""
+import os
+from pathlib import Path
+from types import SimpleNamespace
+from unittest.mock import MagicMock, patch
+
+import pytest
+
+from hermes_cli.config import (
+    _is_inside_container,
+    get_container_exec_info,
+)
+
+
+# =============================================================================
+# _is_inside_container
+# =============================================================================
+
+
+def test_is_inside_container_dockerenv(tmp_path):
+    """Detects /.dockerenv marker file."""
+    with patch("os.path.exists") as mock_exists:
+        mock_exists.side_effect = lambda p: p == "/.dockerenv"
+        assert _is_inside_container() is True
+
+
+def test_is_inside_container_containerenv(tmp_path):
+    """Detects Podman's /run/.containerenv marker."""
+    with patch("os.path.exists") as mock_exists:
+        mock_exists.side_effect = lambda p: p == "/run/.containerenv"
+        assert _is_inside_container() is True
+
+
+def test_is_inside_container_cgroup_docker():
+    """Detects 'docker' in /proc/1/cgroup."""
+    with patch("os.path.exists", return_value=False), \
+         patch("builtins.open", create=True) as mock_open:
+        mock_open.return_value.__enter__ = lambda s: s
+        mock_open.return_value.__exit__ = MagicMock(return_value=False)
+        mock_open.return_value.read = MagicMock(
+            return_value="12:memory:/docker/abc123\n"
+        )
+        assert _is_inside_container() is True
+
+
+def test_is_inside_container_false_on_host():
+    """Returns False when none of the container indicators are present."""
+    with patch("os.path.exists", return_value=False), \
+         patch("builtins.open", side_effect=OSError("no such file")):
+        assert _is_inside_container() is False
+
+
+# =============================================================================
+# get_container_exec_info
+# =============================================================================
+
+
+@pytest.fixture
+def container_env(tmp_path, monkeypatch):
+    """Set up a fake HERMES_HOME with .container-mode file."""
+    hermes_home = tmp_path / ".hermes"
+    hermes_home.mkdir()
+    monkeypatch.setenv("HERMES_HOME", str(hermes_home))
+
+    container_mode = hermes_home / ".container-mode"
+    container_mode.write_text(
+        "# Written by NixOS activation script. Do not edit manually.\n"
+        "backend=podman\n"
+        "container_name=hermes-agent\n"
+        "hermes_bin=/data/current-package/bin/hermes\n"
+    )
+    return hermes_home
+
+
+def test_get_container_exec_info_returns_metadata(container_env):
+    """Reads .container-mode and returns backend/name/bin."""
+    with patch("hermes_cli.config._is_inside_container", return_value=False):
+        info = get_container_exec_info()
+
+    assert info is not None
+    assert info["backend"] == "podman"
+    assert info["container_name"] == "hermes-agent"
+    assert info["hermes_bin"] == "/data/current-package/bin/hermes"
+
+
+def test_get_container_exec_info_none_inside_container(container_env):
+    """Returns None when we're already inside a container."""
+    with patch("hermes_cli.config._is_inside_container", return_value=True):
+        info = get_container_exec_info()
+
+    assert info is None
+
+
+def test_get_container_exec_info_none_without_file(tmp_path, monkeypatch):
+    """Returns None when .container-mode doesn't exist (native mode)."""
+    hermes_home = tmp_path / ".hermes"
+    hermes_home.mkdir()
+    monkeypatch.setenv("HERMES_HOME", str(hermes_home))
+
+    with patch("hermes_cli.config._is_inside_container", return_value=False):
+        info = get_container_exec_info()
+
+    assert info is None
+
+
+def test_get_container_exec_info_defaults():
+    """Falls back to defaults for missing keys."""
+    import tempfile
+
+    with tempfile.TemporaryDirectory() as tmpdir:
+        hermes_home = Path(tmpdir) / ".hermes"
+        hermes_home.mkdir()
+        (hermes_home / ".container-mode").write_text(
+            "# minimal file with no keys\n"
+        )
+
+        with patch("hermes_cli.config._is_inside_container", return_value=False), \
+             patch("hermes_cli.config.get_hermes_home", return_value=hermes_home):
+            info = get_container_exec_info()
+
+        assert info is not None
+        assert info["backend"] == "docker"
+        assert info["container_name"] == "hermes-agent"
+        assert info["hermes_bin"] == "/data/current-package/bin/hermes"
+
+
+def test_get_container_exec_info_docker_backend(container_env):
+    """Correctly reads docker backend."""
+    (container_env / ".container-mode").write_text(
+        "backend=docker\n"
+        "container_name=hermes-custom\n"
+        "hermes_bin=/opt/hermes/bin/hermes\n"
+    )
+
+    with patch("hermes_cli.config._is_inside_container", return_value=False):
+        info = get_container_exec_info()
+
+    assert info["backend"] == "docker"
+    assert info["container_name"] == "hermes-custom"
+    assert info["hermes_bin"] == "/opt/hermes/bin/hermes"
+
+
+# =============================================================================
+# _exec_in_container
+# =============================================================================
+
+
+def test_exec_in_container_calls_execvp():
+    """Verifies os.execvp is called with the correct command."""
+    from hermes_cli.main import _exec_in_container
+
+    container_info = {
+        "backend": "podman",
+        "container_name": "hermes-agent",
+        "hermes_bin": "/data/current-package/bin/hermes",
+    }
+
+    with patch("shutil.which", return_value="/usr/bin/podman"), \
+         patch("subprocess.run") as mock_run, \
+         patch("os.execvp") as mock_exec:
+        # Simulate running container
+        mock_result = MagicMock()
+        mock_result.returncode = 0
+        mock_result.stdout = "true\n"
+        mock_run.return_value = mock_result
+
+        _exec_in_container(container_info, ["chat", "-m", "claude-sonnet-4"])
+
+        mock_exec.assert_called_once_with(
+            "/usr/bin/podman",
+            ["/usr/bin/podman", "exec", "-it", "hermes-agent",
+             "/data/current-package/bin/hermes", "chat", "-m", "claude-sonnet-4"]
+        )
+
+
+def test_exec_in_container_strips_host_flag():
+    """The --host flag is not forwarded into the container."""
+    from hermes_cli.main import _exec_in_container
+
+    container_info = {
+        "backend": "podman",
+        "container_name": "hermes-agent",
+        "hermes_bin": "/data/current-package/bin/hermes",
+    }
+
+    with patch("shutil.which", return_value="/usr/bin/podman"), \
+         patch("subprocess.run") as mock_run, \
+         patch("os.execvp") as mock_exec:
+        mock_result = MagicMock()
+        mock_result.returncode = 0
+        mock_result.stdout = "true\n"
+        mock_run.return_value = mock_result
+
+        _exec_in_container(container_info, ["chat", "--host", "-q", "hello"])
+
+        # --host should be stripped
+        exec_args = mock_exec.call_args[0][1]
+        assert "--host" not in exec_args
+        assert "-q" in exec_args
+        assert "hello" in exec_args
+
+
+def test_exec_in_container_fallback_no_runtime(capsys):
+    """Falls back gracefully when container runtime is not found."""
+    from hermes_cli.main import _exec_in_container
+
+    container_info = {
+        "backend": "podman",
+        "container_name": "hermes-agent",
+        "hermes_bin": "/data/current-package/bin/hermes",
+    }
+
+    with patch("shutil.which", return_value=None), \
+         patch("os.execvp") as mock_exec:
+        _exec_in_container(container_info, ["chat"])
+
+        # Should NOT call execvp — graceful fallback
+        mock_exec.assert_not_called()
+
+    captured = capsys.readouterr()
+    assert "not found on PATH" in captured.err
+
+
+def test_exec_in_container_fallback_container_not_running(capsys):
+    """Falls back when container exists but is not running."""
+    from hermes_cli.main import _exec_in_container
+
+    container_info = {
+        "backend": "docker",
+        "container_name": "hermes-agent",
+        "hermes_bin": "/data/current-package/bin/hermes",
+    }
+
+    with patch("shutil.which", return_value="/usr/bin/docker"), \
+         patch("subprocess.run") as mock_run, \
+         patch("os.execvp") as mock_exec:
+        mock_result = MagicMock()
+        mock_result.returncode = 0
+        mock_result.stdout = "false\n"
+        mock_run.return_value = mock_result
+
+        _exec_in_container(container_info, ["chat"])
+
+        mock_exec.assert_not_called()
+
+    captured = capsys.readouterr()
+    assert "not running" in captured.err
+
+
+def test_exec_in_container_fallback_inspect_fails():
+    """Falls back when docker inspect fails entirely."""
+    from hermes_cli.main import _exec_in_container
+
+    container_info = {
+        "backend": "docker",
+        "container_name": "hermes-agent",
+        "hermes_bin": "/data/current-package/bin/hermes",
+    }
+
+    with patch("shutil.which", return_value="/usr/bin/docker"), \
+         patch("subprocess.run") as mock_run, \
+         patch("os.execvp") as mock_exec:
+        mock_result = MagicMock()
+        mock_result.returncode = 1
+        mock_result.stdout = ""
+        mock_run.return_value = mock_result
+
+        _exec_in_container(container_info, ["chat"])
+
+        mock_exec.assert_not_called()