test: home-dir leak guard for ~/.attune-help/sessions/ (#17)

Session-scoped autouse alarm: fails the suite if any test wrote to the real
~/.attune-help/sessions/ instead of a tmp dir — the regression guard for the
isolation fix in #16. Verified: full suite green (no false positive); a
planted real-dir write trips it and names the file.

specs/test-isolation-guard (layer 1 of 3).

Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>

Author: silversurfer562

tests/conftest.py

@@ -10,6 +10,41 @@
 PLUGIN_ROOT = REPO_ROOT / "plugin"
 PYPROJECT = REPO_ROOT / "pyproject.toml"
 
+# Real home-dir state this layer's tests must never touch (they isolate to a
+# tmp dir instead). The guard below is a regression alarm — see
+# specs/test-isolation-guard/ and the workspace testing-conventions.md.
+_GUARDED_PATHS = [Path.home() / ".attune-help" / "sessions"]
+
+
+def _home_snapshot(p: Path):
+    """Comparable snapshot: dir → child names; file → mtime; absent → None."""
+    if p.is_dir():
+        return frozenset(c.name for c in p.iterdir())
+    if p.exists():
+        return ("file", p.stat().st_mtime)
+    return None
+
+
+@pytest.fixture(scope="session", autouse=True)
+def _guard_real_home_state():
+    """Fail the run if any test wrote to real home-dir state (missing isolation)."""
+    before = {p: _home_snapshot(p) for p in _GUARDED_PATHS}
+    yield
+    leaked = []
+    for p in _GUARDED_PATHS:
+        b, a = before[p], _home_snapshot(p)
+        if isinstance(b, frozenset) or isinstance(a, frozenset):
+            new = (a or frozenset()) - (b or frozenset())
+            if new:
+                leaked.append(f"{p}: new entries {sorted(new)[:5]}")
+        elif b != a:
+            leaked.append(f"{p}: created or modified")
+    assert not leaked, (
+        "Tests wrote to real home-dir state (missing isolation):\n  "
+        + "\n  ".join(leaked)
+        + "\nIsolate via the tmp-dir fixture — see testing-conventions.md."
+    )
+
 
 @pytest.fixture(autouse=True)
 def _isolated_sessions_dir(tmp_path, monkeypatch):