[HaoweiChan]

Why

The track page's cumulative-return chart compared the book against SPY only. Wanted 費半 and 那指 beside it, and a way to hide curves so one volatile line does not flatten the rest.

Task (verbatim): none — untracked work

What changed

• track.track() takes indexes (default none) and adds one cumulative line per index present in the close panel, plus an indexes list in track.json; kuroshio book --provider passes ^SOX and ^IXIC for us* markets and fetches them with the book's names.
• The chart legend is now a row of buttons: each hides or shows its polyline, and the Y axis, zero line and range text rescale to the lines still visible (small inline script, no dependency).
• A track.json written before this change has no indexes and still renders the original four lines.
  Not changed: the book, sleeve and benchmark maths; the TW market (no index lines).

Verification

Gate: ruff 0 errors · pytest 510/510 · 9a37b85
Red-first: test_index_lines_are_tracked_and_each_legend_entry_is_a_toggle written with the feature, not watched red separately
Live: not run — the real provider fetch of ^SOX/^IXIC was not exercised; the toggle was driven in a browser on a synthetic series (hide, rescale, range text)
Not verified: that yfinance returns clean ^SOX / ^IXIC closes on the cron box; until track.json is regenerated the live page shows no new lines

Problems found

none

Follow-ups

none

Reviewer notes

Start here: _track_chart and TRACK_JS in kuroshio/site/render.py
Reproduce: pytest tests/test_track.py -q

🤖 Generated with Claude Code