Fix boundary/child count invariant on shelf and book deletion

When deleting a shelf or book, remove the corresponding boundary from
the parent's boundary list so len(boundaries) == len(children) - 1
is maintained. Add API-level tests covering first, middle, and last
child deletion.

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

src/api.py

@@ -205,11 +205,19 @@ async def update_shelf(shelf_id: str, request: Request) -> dict[str, Any]:
 @router.delete("/api/shelves/{shelf_id}")
 async def delete_shelf(shelf_id: str) -> dict[str, Any]:
     with db.connection() as c:
-        if not db.get_shelf(c, shelf_id):
+        shelf = db.get_shelf(c, shelf_id)
+        if not shelf:
             raise HTTPException(404, "Shelf not found")
         photos = db.collect_shelf_photos(c, shelf_id)
+        rank = db.get_shelf_rank(c, shelf_id)
+        cab = db.get_cabinet(c, shelf.cabinet_id)
     with db.transaction() as c:
         db.delete_shelf(c, shelf_id)
+        if cab:
+            bounds: list[float] = json.loads(cab.shelf_boundaries) if cab.shelf_boundaries else []
+            if bounds:
+                del bounds[min(rank, len(bounds) - 1)]
+                db.set_cabinet_boundaries(c, cab.id, json.dumps(bounds))
     for fn in photos:
         del_photo(fn)
     return {"ok": True}
@@ -293,11 +301,19 @@ async def update_book(book_id: str, request: Request) -> dict[str, Any]:
 @router.delete("/api/books/{book_id}")
 async def delete_book(book_id: str) -> dict[str, Any]:
     with db.connection() as c:
-        if not db.get_book(c, book_id):
+        book = db.get_book(c, book_id)
+        if not book:
             raise HTTPException(404, "Book not found")
         fn = db.get_book_photo(c, book_id)
+        rank = db.get_book_rank(c, book_id)
+        shelf = db.get_shelf(c, book.shelf_id)
     with db.transaction() as c:
         db.delete_book(c, book_id)
+        if shelf:
+            bounds: list[float] = json.loads(shelf.book_boundaries) if shelf.book_boundaries else []
+            if bounds:
+                del bounds[min(rank, len(bounds) - 1)]
+                db.set_shelf_boundaries(c, shelf.id, json.dumps(bounds))
     del_photo(fn)
     return {"ok": True}