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>

tests/test_api.py

@@ -0,0 +1,157 @@
+"""API-level integration tests.
+
+Uses a minimal FastAPI app (router only, no lifespan) so tests run against
+a temporary SQLite database without needing config or plugins.
+"""
+
+import json
+from collections.abc import Iterator
+from pathlib import Path
+
+import pytest
+from fastapi import FastAPI
+from fastapi.testclient import TestClient
+
+import db
+import files
+from api import router
+
+# ── Fixtures ──────────────────────────────────────────────────────────────────
+
+_app = FastAPI()
+_app.include_router(router)
+
+
+@pytest.fixture
+def client(tmp_path: Path, monkeypatch: pytest.MonkeyPatch) -> Iterator[TestClient]:
+    """TestClient backed by a fresh temporary database."""
+    monkeypatch.setattr(db, "DB_PATH", tmp_path / "test.db")
+    monkeypatch.setattr(files, "DATA_DIR", tmp_path)
+    monkeypatch.setattr(files, "IMAGES_DIR", tmp_path / "images")
+    files.init_dirs()
+    db.init_db()
+    db.COUNTERS.clear()
+    with TestClient(_app) as c:
+        yield c
+    db.COUNTERS.clear()
+
+
+def _seed(tmp_path: Path) -> dict[str, str]:
+    """Create room/cabinet/shelves/books with boundaries via db helpers; return their IDs."""
+    with db.transaction() as c:
+        room = db.create_room(c)
+        cab = db.create_cabinet(c, room.id)
+        s_a = db.create_shelf(c, cab.id)
+        s_b = db.create_shelf(c, cab.id)
+        s_c = db.create_shelf(c, cab.id)
+        b_a = db.create_book(c, s_a.id)
+        b_b = db.create_book(c, s_a.id)
+        b_c = db.create_book(c, s_a.id)
+        # 3 shelves → 2 interior boundaries
+        db.set_cabinet_boundaries(c, cab.id, json.dumps([0.33, 0.66]))
+        # 3 books in shelf_a → 2 interior boundaries
+        db.set_shelf_boundaries(c, s_a.id, json.dumps([0.33, 0.66]))
+    return {
+        "room": room.id,
+        "cabinet": cab.id,
+        "shelf_a": s_a.id,
+        "shelf_b": s_b.id,
+        "shelf_c": s_c.id,
+        "book_a": b_a.id,
+        "book_b": b_b.id,
+        "book_c": b_c.id,
+    }
+
+
+# ── Shelf deletion / boundary cleanup ─────────────────────────────────────────
+
+
+def test_delete_first_shelf_removes_first_boundary(
+    client: TestClient, tmp_path: Path, monkeypatch: pytest.MonkeyPatch
+) -> None:
+    monkeypatch.setattr(db, "DB_PATH", tmp_path / "test.db")
+    ids = _seed(tmp_path)
+    resp = client.delete(f"/api/shelves/{ids['shelf_a']}")
+    assert resp.status_code == 200
+    with db.connection() as c:
+        cab = db.get_cabinet(c, ids["cabinet"])
+    assert cab is not None
+    bounds = json.loads(cab.shelf_boundaries or "[]")
+    assert bounds == [0.66]  # first boundary (0.33) removed
+
+
+def test_delete_middle_shelf_removes_middle_boundary(
+    client: TestClient, tmp_path: Path, monkeypatch: pytest.MonkeyPatch
+) -> None:
+    monkeypatch.setattr(db, "DB_PATH", tmp_path / "test.db")
+    ids = _seed(tmp_path)
+    resp = client.delete(f"/api/shelves/{ids['shelf_b']}")
+    assert resp.status_code == 200
+    with db.connection() as c:
+        cab = db.get_cabinet(c, ids["cabinet"])
+    assert cab is not None
+    bounds = json.loads(cab.shelf_boundaries or "[]")
+    assert bounds == [0.33]  # middle boundary (0.66) removed
+
+
+def test_delete_last_shelf_removes_last_boundary(
+    client: TestClient, tmp_path: Path, monkeypatch: pytest.MonkeyPatch
+) -> None:
+    monkeypatch.setattr(db, "DB_PATH", tmp_path / "test.db")
+    ids = _seed(tmp_path)
+    resp = client.delete(f"/api/shelves/{ids['shelf_c']}")
+    assert resp.status_code == 200
+    with db.connection() as c:
+        cab = db.get_cabinet(c, ids["cabinet"])
+    assert cab is not None
+    bounds = json.loads(cab.shelf_boundaries or "[]")
+    assert bounds == [0.33]  # last boundary (0.66) removed
+
+
+def test_delete_only_shelf_leaves_no_boundaries(
+    client: TestClient, tmp_path: Path, monkeypatch: pytest.MonkeyPatch
+) -> None:
+    """Deleting the sole shelf (no boundaries) leaves boundaries unchanged (empty)."""
+    monkeypatch.setattr(db, "DB_PATH", tmp_path / "test.db")
+    ids = _seed(tmp_path)
+    # Delete two shelves first to leave only one
+    client.delete(f"/api/shelves/{ids['shelf_b']}")
+    client.delete(f"/api/shelves/{ids['shelf_c']}")
+    resp = client.delete(f"/api/shelves/{ids['shelf_a']}")
+    assert resp.status_code == 200
+    with db.connection() as c:
+        cab = db.get_cabinet(c, ids["cabinet"])
+    assert cab is not None
+    bounds = json.loads(cab.shelf_boundaries or "[]")
+    assert bounds == []
+
+
+# ── Book deletion / boundary cleanup ──────────────────────────────────────────
+
+
+def test_delete_first_book_removes_first_boundary(
+    client: TestClient, tmp_path: Path, monkeypatch: pytest.MonkeyPatch
+) -> None:
+    monkeypatch.setattr(db, "DB_PATH", tmp_path / "test.db")
+    ids = _seed(tmp_path)
+    resp = client.delete(f"/api/books/{ids['book_a']}")
+    assert resp.status_code == 200
+    with db.connection() as c:
+        shelf = db.get_shelf(c, ids["shelf_a"])
+    assert shelf is not None
+    bounds = json.loads(shelf.book_boundaries or "[]")
+    assert bounds == [0.66]
+
+
+def test_delete_last_book_removes_last_boundary(
+    client: TestClient, tmp_path: Path, monkeypatch: pytest.MonkeyPatch
+) -> None:
+    monkeypatch.setattr(db, "DB_PATH", tmp_path / "test.db")
+    ids = _seed(tmp_path)
+    resp = client.delete(f"/api/books/{ids['book_c']}")
+    assert resp.status_code == 200
+    with db.connection() as c:
+        shelf = db.get_shelf(c, ids["shelf_a"])
+    assert shelf is not None
+    bounds = json.loads(shelf.book_boundaries or "[]")
+    assert bounds == [0.33]