feat: add per-book reading journal notes

Claude-Session: https://claude.ai/code/session_01M9MLit5Ko3X4s7rzC5Kv7X

backend/notes.py

@@ -1,4 +1,77 @@
-"""Notes slice: a per-book reading journal."""
-from flask import Blueprint
+"""Notes slice: a per-book reading journal. Ownership is always derived through books.user_id."""
+from flask import Blueprint, g, jsonify
+
+from auth import login_required
+from db import query, query_one
+from validation import ApiError, json_body, text
 
 bp = Blueprint("notes", __name__, url_prefix="/api")
+
+MAX_BODY = 10_000
+NOTE_COLUMNS = "n.id, n.book_id, n.body, n.created_at, n.updated_at"
+
+
+def to_json(row: dict) -> dict:
+    return {
+        "id": row["id"],
+        "book_id": row["book_id"],
+        "body": row["body"],
+        "created_at": row["created_at"].isoformat(),
+        "updated_at": row["updated_at"].isoformat(),
+    }
+
+
+def _require_book(book_id: int) -> None:
+    if query_one("SELECT 1 FROM books WHERE id = %s AND user_id = %s", (book_id, g.user_id)) is None:
+        raise ApiError(404, "Book not found")
+
+
+@bp.get("/books/<int(max=2147483647):book_id>/notes")
+@login_required
+def list_notes(book_id: int):
+    _require_book(book_id)
+    rows = query(
+        f"SELECT {NOTE_COLUMNS} FROM notes n WHERE n.book_id = %s ORDER BY n.created_at DESC, n.id DESC",
+        (book_id,),
+    )
+    return jsonify([to_json(row) for row in rows])
+
+
+@bp.post("/books/<int(max=2147483647):book_id>/notes")
+@login_required
+def add_note(book_id: int):
+    _require_book(book_id)
+    body = text(json_body({"body"}), "body", MAX_BODY)
+    row = query_one(f"INSERT INTO notes AS n (book_id, body) VALUES (%s, %s) RETURNING {NOTE_COLUMNS}", (book_id, body))
+    return jsonify(to_json(row)), 201
+
+
+@bp.patch("/notes/<int(max=2147483647):note_id>")
+@login_required
+def update_note(note_id: int):
+    body = text(json_body({"body"}), "body", MAX_BODY)
+    row = query_one(
+        f"""
+        UPDATE notes n
+           SET body = %s, updated_at = now()
+          FROM books b
+         WHERE n.id = %s AND b.id = n.book_id AND b.user_id = %s
+        RETURNING {NOTE_COLUMNS}
+        """,
+        (body, note_id, g.user_id),
+    )
+    if row is None:
+        raise ApiError(404, "Note not found")
+    return jsonify(to_json(row))
+
+
+@bp.delete("/notes/<int(max=2147483647):note_id>")
+@login_required
+def delete_note(note_id: int):
+    row = query_one(
+        "DELETE FROM notes n USING books b WHERE n.id = %s AND b.id = n.book_id AND b.user_id = %s RETURNING n.id",
+        (note_id, g.user_id),
+    )
+    if row is None:
+        raise ApiError(404, "Note not found")
+    return "", 204