Self-contained, skip-friendly lab starting points (#103)

Co-authored-by: claude <claude@jpaul.io>
Co-committed-by: claude <claude@jpaul.io>

modules/10-reviewing-code-you-didnt-write/lab/start/tasks.py

@@ -0,0 +1,42 @@
+"""Core task logic for the demo app.
+
+Same running example as Modules 1 and 2, with one addition: `complete` now validates the
+index and raises a clear error for a bad one. That explicit edge-case handling is here on
+purpose; it's the kind of thing an AI "refactor" likes to quietly remove. This is the
+known-good base you'll review an AI change against in Module 10.
+"""
+
+from dataclasses import dataclass, field
+
+
+@dataclass
+class Task:
+    title: str
+    done: bool = False
+
+
+@dataclass
+class TaskList:
+    tasks: list[Task] = field(default_factory=list)
+
+    def add(self, title: str) -> Task:
+        task = Task(title=title)
+        self.tasks.append(task)
+        return task
+
+    def complete(self, index: int) -> None:
+        if not 0 <= index < len(self.tasks):
+            raise IndexError(f"no task at index {index}")
+        self.tasks[index].done = True
+
+    def pending(self) -> list[Task]:
+        return [t for t in self.tasks if not t.done]
+
+    def render(self) -> str:
+        if not self.tasks:
+            return "(no tasks yet)"
+        lines = []
+        for i, task in enumerate(self.tasks):
+            box = "[x]" if task.done else "[ ]"
+            lines.append(f"{i}. {box} {task.title}")
+        return "\n".join(lines)