test: isolate HOME for the unit suite (hermetic audit/queue/state)

The unit suite could write to and flock the real ~/.bot-bottle: state,
queue, and audit dirs all derive from supervise.bot_bottle_root() ->
Path.home(). A test taking a flock on the real audit log blocks
indefinitely when a live bottle's supervise sidecar holds that lock
(observed: a `coverage run` hung at 0% CPU), and unisolated tests
otherwise pollute the developer's home dir.

Point HOME at a throwaway temp dir for the whole tests/unit package
(restored + cleaned at exit). Tests that set their own HOME now restore
to the isolated dir, not the real one; tests that patch bot_bottle_root
directly are unaffected.

Closes #302

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01NkwFXLFff9PYPy4wgVBJp9

tests/unit/__init__.py

@@ -0,0 +1,37 @@
+"""Unit-test package init.
+
+Isolates ``HOME`` to a throwaway directory for the entire unit suite so
+no test ever reads or writes the real ``~/.bot-bottle`` (state, queue,
+and audit dirs all derive from ``supervise.bot_bottle_root()`` →
+``Path.home()``). Without this, a test that takes a ``flock`` on the
+real audit log can **block indefinitely** when a live bottle's supervise
+sidecar holds that lock — observed as a hung ``coverage run`` at 0% CPU —
+and unisolated tests otherwise pollute the developer's home dir.
+
+Individual tests that need their own ``HOME`` still override
+``os.environ['HOME']`` and restore it; they now restore to this isolated
+dir rather than the real one, so isolation holds either way. Tests that
+patch ``supervise.bot_bottle_root`` directly are unaffected.
+"""
+
+from __future__ import annotations
+
+import atexit
+import os
+import shutil
+import tempfile
+
+_real_home = os.environ.get("HOME")
+_tmp_home = tempfile.mkdtemp(prefix="bot-bottle-unit-home.")
+os.environ["HOME"] = _tmp_home
+
+
+def _restore_home() -> None:
+    if _real_home is None:
+        os.environ.pop("HOME", None)
+    else:
+        os.environ["HOME"] = _real_home
+    shutil.rmtree(_tmp_home, ignore_errors=True)
+
+
+atexit.register(_restore_home)