[HaoweiChan]

Why

The track page's cumulative-return chart had no value axis, no gridlines and oversized labels, so it read as a sketch: the reader could not tell what a line's height meant or what any day's values were.

Task (verbatim): none — untracked work

What changed

• The chart is drawn in the browser from the series embedded on its container (trackDraw in TRACK_JS) at the container's real width, so type stays 11px at any size and redraws on resize.
• Y axis with percent ticks and hairline gridlines, a stronger zero line, date ticks every 1–2 weeks, an end-point dot per line, thinner reference lines (dashed) against a heavier book line.
• Hover (or touch-drag) shows a crosshair, a dot on every visible line and a tooltip with that day's values, ranked.
• Legend toggles from PR 68 still hide a line and now rescale the axis through the same draw; the "range" caption is gone because the axis shows it.
  Not changed: the series data, the stats row, the legend values.

Verification

Gate: ruff 0 errors in the committed tree · pytest 511/511 · f1c5c48
Red-first: test_chart_carries_its_series_and_labels_the_actual_benchmark written with the change, not watched red separately
Live: not run — drawn and driven (hover, toggle, 375px width) in a browser against the real latest track.json; the deployed site is not yet rebuilt
Not verified: older browsers without ResizeObserver or pointer events

Problems found

none

Follow-ups

none

Reviewer notes

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

🤖 Generated with Claude Code