Isolate mock_paths fixture from host MOUNT_ROOT config; simplify probe_target mount check

mock_paths patched TARGET_DIR/PENDING_DIR/etc but not MOUNT_ROOT, so tests leaked the host's real ~/pCloudDrive mount_root config and failed probe_target's mountpoint check. Also drop redundant equality clause since is_relative_to already covers equal paths, and document the mount precondition.

coe_mirror.py

@@ -168,13 +168,16 @@ def release_lock(lock_fd: int) -> None:
 
 
 def probe_target() -> bool:
-    """Probe target directory health. Write tiny file, read back, delete. Return True if healthy."""
+    """Probe target directory health. Write tiny file, read back, delete. Return True if healthy.
+
+    When MOUNT_ROOT is configured, first verify it is a live mountpoint and TARGET_DIR is under it; return False (queue to pending) otherwise.
+    """
     try:
         if MOUNT_ROOT is not None:
             if not MOUNT_ROOT.exists() or not os.path.ismount(str(MOUNT_ROOT)):
                 logger.warning("mount_root %s is not a live mountpoint; target unavailable; queuing locally", MOUNT_ROOT)
                 return False
-            if not (TARGET_DIR == MOUNT_ROOT or TARGET_DIR.is_relative_to(MOUNT_ROOT)):
+            if not TARGET_DIR.is_relative_to(MOUNT_ROOT):
                 logger.warning("target_dir %s is not under configured mount_root %s; misconfig; queuing locally", TARGET_DIR, MOUNT_ROOT)
                 return False
 

tests/test_coe_mirror.py

@@ -37,6 +37,7 @@ def mock_paths(tmp_path, monkeypatch):
     pending_dir.mkdir()
     log_dir.mkdir()
 
+    monkeypatch.setattr(coe_mirror, "MOUNT_ROOT", None)
     monkeypatch.setattr(coe_mirror, "TARGET_DIR", target_dir)
     monkeypatch.setattr(coe_mirror, "PENDING_DIR", pending_dir)
     monkeypatch.setattr(coe_mirror, "LOG_DIR", log_dir)