TaskSequence in tasks/common.py is unused

tasks/common.py defines a TaskSequence(Task) class (curriculum-style sequential SFT), but nothing in the repo references it:

• No callers in scripts/ — chat_sft.py constructs TaskMixture only.
• Not imported by any test — tests/test_tasks.py imports Task, TaskMixture, HubDataset, render_mc.
• No dynamic construction (no getattr / importlib / string-name lookup); tasks/ has no __init__.py re-export, and it isn't exported via pyproject.toml.
• Its only ever reference — the import in scripts/chat_sft.py — was already removed in 190d951 ("delete unused imports"), which left the class body orphaned.

The only remaining mention is the README.md file-tree comment (TaskMixture | TaskSequence).

Is TaskSequence meant to stay as an illustrative curriculum example, or is it safe to remove? Happy to send a PR either way.

(Found while validating a static dead-code analyzer against real-world repos using Cursor + Vinv AI)