tests: collecting test_budget_view never reads the host's leisure switch

Its module-level rules_for runs before any autouse fixture, so a live
/etc/leisure-watch/leisure_from priced RULES. collection_isolated()
points every switch reader at a path that cannot exist.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Dsh4Znwh2KnC7q6vbGpX1N

steam_backlog_enforcer/tests/_isolate_leisure.py

@@ -10,10 +10,16 @@ Phase 2 on by writing a date to :func:`switch_file`.
 The leisure kill scan reads ``/proc`` through its own constant; it gets an
 empty directory (:func:`leisure_proc`), so no test can see -- or signal -- a
 live browser or player.
+
+Module-level code runs at collection, before any fixture: it wraps itself in
+:func:`collection_isolated` instead.
 """
 
 from __future__ import annotations
 
+from contextlib import ExitStack, contextmanager
+import os
+from pathlib import Path
 from typing import TYPE_CHECKING
 from unittest.mock import patch
 
@@ -21,10 +27,25 @@ import pytest
 
 if TYPE_CHECKING:
     from collections.abc import Iterator
-    from pathlib import Path
 
 _SWITCH_NAME = "leisure_from"
 _PROC_NAME = "leisure_proc"
+# Every switch reader, by the module attribute it looks up at call time.
+_SWITCH_READERS = (
+    "earned_time._leisure.LEISURE_FROM_PATH",
+    "steam_backlog_enforcer._leisure_mode.LEISURE_FROM_PATH",
+)
+# Can never exist (/dev/null is not a directory): always the parked date.
+_NO_SWITCH = Path(os.devnull) / _SWITCH_NAME
+
+
+@contextmanager
+def collection_isolated() -> Iterator[None]:
+    """Point every switch reader at a file that cannot exist (no ``tmp_path``)."""
+    with ExitStack() as stack:
+        for target in _SWITCH_READERS:
+            stack.enter_context(patch(target, _NO_SWITCH))
+        yield
 
 
 def switch_file(tmp_path: Path) -> Path:
@@ -44,9 +65,8 @@ def _isolate_leisure(tmp_path: Path) -> Iterator[None]:
     switch.parent.mkdir(exist_ok=True)
     proc = leisure_proc(tmp_path)
     proc.mkdir(exist_ok=True)
-    with (
-        patch("earned_time._leisure.LEISURE_FROM_PATH", switch),
-        patch("steam_backlog_enforcer._leisure_mode.LEISURE_FROM_PATH", switch),
-        patch("steam_backlog_enforcer._leisure_procs._PROC", proc),
-    ):
+    with ExitStack() as stack:
+        for target in _SWITCH_READERS:
+            stack.enter_context(patch(target, switch))
+        stack.enter_context(patch("steam_backlog_enforcer._leisure_procs._PROC", proc))
         yield

steam_backlog_enforcer/tests/test_budget_view.py

@@ -22,6 +22,7 @@ from steam_backlog_enforcer._budget_view import (
 from steam_backlog_enforcer._playtime_history import HistoryDay
 from steam_backlog_enforcer._playtime_state import PlaytimeState, rules_for
 from steam_backlog_enforcer.config import Config
+from steam_backlog_enforcer.tests._isolate_leisure import collection_isolated
 from steam_backlog_enforcer.tests._no_workout_http import earned_budget, fixed_budget
 
 # Built at import time, so the autouse _no_workout_http fixture is not in
@@ -30,8 +31,10 @@ from steam_backlog_enforcer.tests._no_workout_http import earned_budget, fixed_b
 # have earned. Stub it explicitly so the constant is the earned budget always.
 # The held budget is pinned for the same reason: conftest's redirects are not
 # active at import either, so rules_for would read the LIVE playtime_state.json
-# and hold RULES at whatever high-water mark it records today.
+# and hold RULES at whatever high-water mark it records today. Nor would the
+# leisure switch be: the host's /etc/leisure-watch/leisure_from would price it.
 with (
+    collection_isolated(),
     patch("steam_backlog_enforcer._playtime_state.held_today", return_value=0.0),
     patch(
         "steam_backlog_enforcer._playtime_state.resolve_budget",

steam_backlog_enforcer/tests/test_budget_view_collection.py

@@ -0,0 +1,32 @@
+"""Collecting test_budget_view never reads the host's leisure switch file."""
+
+from __future__ import annotations
+
+import importlib
+from typing import TYPE_CHECKING
+from unittest.mock import patch
+
+from steam_backlog_enforcer._playtime_state import rules_for
+from steam_backlog_enforcer.config import Config
+from steam_backlog_enforcer.tests import test_budget_view
+from steam_backlog_enforcer.tests._no_workout_http import earned_budget
+
+if TYPE_CHECKING:
+    from pathlib import Path
+
+
+def test_a_live_host_switch_does_not_leak_into_rules(tmp_path: Path) -> None:
+    with (
+        patch("steam_backlog_enforcer._playtime_state.held_today", return_value=0.0),
+        patch(
+            "steam_backlog_enforcer._playtime_state.resolve_budget",
+            side_effect=earned_budget,
+        ),
+    ):
+        dormant = rules_for(Config(), demo=False)
+    # The host went live long ago: what the import-time read would see.
+    host = tmp_path / "host_leisure_from"
+    host.write_text("2000-01-01\n", encoding="utf-8")
+    with patch("earned_time._leisure.LEISURE_FROM_PATH", host):
+        reloaded = importlib.reload(test_budget_view)
+    assert dormant == reloaded.RULES