fix(watch): the owner's folder choice must never be overwritten

Two bugs found while filing the Obsidian Sorter note itself:

1. proposed_toc went stale when proposed_folder was edited by hand.
   The watcher now re-resolves the index line from the folder on every pass.

2. Re-proposing after a body edit clobbered a hand-edited proposed_folder.
   The watcher's own suggestion is now kept separately in
   proposed_folder_auto, so a difference marks a human choice, which wins.

Adds two guard tests. 17/17 passing.

tests/run_tests.py

@@ -326,6 +326,29 @@ def main() -> int:
             except OSError:
                 pass
 
+        # ---- watcher: the owner's hand-picked folder must survive ----------
+        from sorter.watch import user_selected_folder
+        from sorter.models import Note as _Note
+
+        def _n(chosen, auto):
+            return _Note(path="x", rel_path="010 inbox/x.md", filename="x.md",
+                         stem="x", title="x", note_type="note", status=None,
+                         fm={"proposed_folder": chosen, "proposed_folder_auto": auto})
+
+        if user_selected_folder(_n("300 areas/A", "200 projects/B")) == "300 areas/A":
+            print("PASS  guard: a hand-edited folder is treated as the owner's choice")
+            passed += 1
+        else:
+            details.append("FAIL  guard: hand-edited folder not detected")
+            failed += 1
+
+        if user_selected_folder(_n("200 projects/B", "200 projects/B")) is None:
+            print("PASS  guard: an untouched proposal is not treated as customised")
+            passed += 1
+        else:
+            details.append("FAIL  guard: untouched proposal wrongly seen as customised")
+            failed += 1
+
         # ---- inbox cleared --------------------------------------------------
         left = [p for p in (vault / args.inbox).glob("*.md")
                 if not p.name.startswith("_")]