CM-71972: Name the home fixture without the underscore prefix

An underscore prefix marks a fixture as side-effect-only, and ruff's PT019
asks for usefixtures in that case. This one returns the scratch home the
skill tests write into, so the value is used and the name should say so.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

Author: Altruistus

tests/cli/commands/ai_guardrails/test_session_start_command.py

@@ -32,7 +32,7 @@ def _isolated_session_context_cache(tmp_path: Path, monkeypatch: pytest.MonkeyPa
 
 
 @pytest.fixture(autouse=True)
-def _isolated_home(tmp_path: Path, monkeypatch: pytest.MonkeyPatch) -> Path:
+def isolated_home(tmp_path: Path, monkeypatch: pytest.MonkeyPatch) -> Path:
     """Point every home-relative lookup at a scratch directory.
 
     The skills sweep walks the filesystem rather than going through a collector these tests
@@ -632,15 +632,15 @@ def test_reports_skill_files(
     mock_collect: MagicMock,
     mock_load_config: MagicMock,
     mock_ctx: MagicMock,
-    _isolated_home: Path,
+    isolated_home: Path,
 ) -> None:
     """User-scope skills ride alongside the MCP inventory in the same report."""
     mock_get_auth.return_value = MagicMock(tenant_id='tenant-1')
     mock_ai_client = MagicMock()
     mock_get_client.return_value = mock_ai_client
     mock_collect.return_value = ({}, {})
     content = '---\nname: dummy-skill\n---\nBody.\n'
-    skill_file = _write_claude_skill(_isolated_home, 'dummy-skill', content)
+    skill_file = _write_claude_skill(isolated_home, 'dummy-skill', content)
     skills = [{'path': str(skill_file), 'content': content}]
 
     payload = {'session_id': 'session-123'}
@@ -671,7 +671,7 @@ def test_editing_a_skill_re_reports(
     mock_collect: MagicMock,
     mock_load_config: MagicMock,
     mock_ctx: MagicMock,
-    _isolated_home: Path,
+    isolated_home: Path,
 ) -> None:
     """Skill bodies are part of the dedup digest, so an edit sends a fresh report."""
     mock_get_auth.return_value = MagicMock(tenant_id='tenant-1')
@@ -680,7 +680,7 @@ def test_editing_a_skill_re_reports(
     mock_collect.return_value = ({}, {})
     payload = json.dumps({'session_id': 'session-123'})
 
-    _write_claude_skill(_isolated_home, 'dummy-skill', 'first')
+    _write_claude_skill(isolated_home, 'dummy-skill', 'first')
     with patch('sys.stdin', new=StringIO(payload)):
         session_start_command(mock_ctx, ide='claude-code')
 
@@ -689,7 +689,7 @@ def test_editing_a_skill_re_reports(
         session_start_command(mock_ctx, ide='claude-code')
     assert mock_ai_client.report_session_context.call_count == 1
 
-    _write_claude_skill(_isolated_home, 'dummy-skill', 'edited')
+    _write_claude_skill(isolated_home, 'dummy-skill', 'edited')
     with patch('sys.stdin', new=StringIO(payload)):
         session_start_command(mock_ctx, ide='claude-code')
     assert mock_ai_client.report_session_context.call_count == 2