fix: resolve hooks_cli.py merge conflict + add mine_global_lock tests

- Resolve UU conflict in hooks_cli.py: take develop/HEAD approach
  (mine synchronously via _mine_sync, then pass through unconditionally).
  _mine_sync already catches subprocess.TimeoutExpired — fixes Copilot #1.
- Add tests/test_palace_locks.py: 4 tests covering mine_global_lock
  non-blocking semantics (acquire, second-acquire raises MineAlreadyRunning,
  reusable after release, release on exception) — fixes Copilot #4.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

tests/test_palace_locks.py

@@ -0,0 +1,59 @@
+"""Tests for mine_global_lock: non-blocking cross-process lock semantics."""
+import threading
+
+import pytest
+
+from mempalace.palace import MineAlreadyRunning, mine_global_lock
+
+
+def test_mine_global_lock_acquired(tmp_path, monkeypatch):
+    """Lock is acquired and released without error."""
+    monkeypatch.setenv("HOME", str(tmp_path))
+    with mine_global_lock():
+        pass  # should not raise
+
+
+def test_mine_global_lock_second_acquire_raises(tmp_path, monkeypatch):
+    """Concurrent second acquire raises MineAlreadyRunning."""
+    monkeypatch.setenv("HOME", str(tmp_path))
+    results: list[str] = []
+
+    with mine_global_lock():
+        # While this lock is held, spawn a thread that tries to acquire.
+        def try_acquire():
+            try:
+                with mine_global_lock():
+                    results.append("acquired")
+            except MineAlreadyRunning:
+                results.append("blocked")
+
+        t = threading.Thread(target=try_acquire)
+        t.start()
+        t.join(timeout=5)
+
+    assert results == ["blocked"]
+
+
+def test_mine_global_lock_reusable_after_release(tmp_path, monkeypatch):
+    """Lock can be re-acquired after the context manager exits."""
+    monkeypatch.setenv("HOME", str(tmp_path))
+
+    with mine_global_lock():
+        pass  # first acquire + release
+
+    # Second acquire must succeed; MineAlreadyRunning would propagate as failure.
+    with mine_global_lock():
+        pass
+
+
+def test_mine_global_lock_exception_still_releases(tmp_path, monkeypatch):
+    """Lock is released even when the body raises."""
+    monkeypatch.setenv("HOME", str(tmp_path))
+
+    with pytest.raises(ValueError):
+        with mine_global_lock():
+            raise ValueError("boom")
+
+    # Must be acquirable again after the exception.
+    with mine_global_lock():
+        pass