Stragglers and backup tasks in your MapReduce lab implementation

Add speculative backup tasks, inject a slow worker, and compare job completion times with and without speculation over repeated runs, as a small reproduction of a paper claim.

The exercise happens on Self-directed extension of MIT 6.5840 Lab 1. Canonical link: https://pdos.csail.mit.edu/6.5840/labs/lab-mr.html. Link check: link responded (5 Oct 2026). Opened from this app 0 times; opening is not counted as an attempt.

Supports: Practice reproducing an empirical systems claim qualitatively; keep lab solutions private per the course policy.