debug_runtime_errorlisted

# debug_runtime_error Runtime errors have a specific anatomy. Reading them systematically is faster than guessing. This skill gives you a repeatable process for going from "error message" to "root cause and fix" as quickly as possible. ## Step 1: Read the Full Stack Trace — Don't Skip to the Bottom Most people instinctively read only the last line of a stack trace (the error message). That's often the symptom, not the cause. The most useful frame is usually **the highest frame in YOUR code** (not a library or framework frame). **Anatomy of a Python traceback:** ``` Traceback (most recent call last): ← read from here File "app/api/orders.py", line 42, in create_order ← YOUR code result = order_service.place(data) File "app/services/order_service.py", line 18, in place ← YOUR code user = self.user_repo.find_by_id(data['user_id']) File "app/repos/user_repo.py", line 31, in find_by_id ← YOUR code return self.db.execute(query).scalar_one() File "sqlalchemy/orm/session.py", line 1203, in scalar_one ← LIBRARY raise NoResultFound(...) sqlalchemy.exc.NoResultFound: No row was found for one() ← the symptom ``` The root cause here isn't SQLAlchemy — it's that `data['user_id']` contains an ID that doesn't exist in the database, or the wrong ID is being passed. **Rule:** Find the last frame that's in YOUR code. That's where your investigation starts. ## Step 2: Understand the Error Type Different error types point to different categories of