Fix kill switch not cleared on reinstall; guard midclt delete; tighten sitecustomize imports

install.sh: running install.sh after a recover.sh left /data/truecloud-patch/disabled
in place, so apply.sh silently skipped all patching and middlewared restarted
without the patch. Clear the kill switch file before running apply.sh.

uninstall.sh: midclt initshutdownscript.delete was unguarded under set -euo pipefail,
so a delete failure (already-removed entry, transient API error) aborted the script
before sitecustomize.py was cleaned up or /data/truecloud-patch/ was removed. Now
guarded with an if/else that warns and continues.

sitecustomize.py: move importlib.machinery/.util imports inside the if block in
find_spec so they only execute when intercepting our two target modules, not on
every module import across the whole process. In _install(), import os before
importlib.util so the kill switch check (cheap) runs before the importlib import
(slightly heavier on first use). Remove the unused orig variable in _patch_restic.

patch_ui.py: add explicit encoding="utf-8" to both open() calls. errors="replace"
on read so malformed bytes in a bundle don't silently skip a candidate file.

patch/sitecustomize.py

@@ -41,14 +41,14 @@ class _Finder:
         self._done = set()      # modules already patched
 
     def find_spec(self, fullname, path, target=None):  # noqa: ARG002
-        import importlib.machinery
-        import importlib.util
-
         if (
             fullname in self._targets
             and fullname not in self._done
             and fullname not in self._loading
         ):
+            import importlib.machinery
+            import importlib.util
+
             # Find the real file spec HERE, before Python adds the module to
             # sys.modules.  If we deferred this to exec_module, find_spec would
             # short-circuit via sys.modules[fullname].__spec__ (our own spec) and
@@ -135,8 +135,7 @@ def _patch_b2(module):
 
 
 def _patch_restic(module):
-    orig = module.get_restic_config
-    if getattr(orig, "_truecloud_patched", False):
+    if getattr(module.get_restic_config, "_truecloud_patched", False):
         return
 
     # ResticConfig is safe to capture now (it's a dataclass defined in the module).
@@ -182,10 +181,10 @@ _PATCHES = {
 # ── Entry point ───────────────────────────────────────────────────────────────
 
 def _install():
-    import importlib.util
     import os
     if os.path.exists("/data/truecloud-patch/disabled"):
         return  # kill switch: touch /data/truecloud-patch/disabled to bypass this hook
+    import importlib.util
     if importlib.util.find_spec("middlewared") is None:
         return  # not a middlewared Python process; nothing to do
     sys.meta_path.append(_Finder())