fix: Close tooltip when cursor leaves chart via y-axis

[Who-is-PS]

Description

When hovering over a line chart and moving the cursor toward the y-axis labels, the tooltip stays open even after the cursor has completely left the chart area.

Root cause

Two issues in onSVGMouseOut and onPopoverLeave:

1. onSVGMouseOut used a coordinate-based isMouseOverPopover check with a 12px deadzone around the popover's bounding rect. When the popover is positioned near the y-axis, the cursor's exit coordinates often fell within this deadzone — causing cleanup to be skipped.

2. onPopoverLeave only cleared highlights when the mouse moved back into the SVG (nodeContains(svg, relatedTarget)). When the mouse exited the popover toward the outside (y-axis exit path), nothing cleared the tooltip.

Solution

1. onSVGMouseOut: Replaced the coordinate-based isMouseOverPopover check with a DOM-based nodeContains check using popoverRef.current?.parentElement (which includes the transition wrapper). Cleanup is only suppressed when the mouse actually enters the popover DOM tree.

2. onPopoverLeave: Simplified to unconditionally clear highlights when the mouse leaves the popover (unless handlers are disabled). When mouse returns to the SVG, onSVGMouseMove naturally re-triggers the correct tooltip.

The isMouseOverPopover deadzone check is preserved in onSVGMouseMove where it remains useful for preventing tooltip flickering.

Changes

• src/mixed-line-bar-chart/hooks/use-mouse-hover.ts — Updated onSVGMouseOut and onPopoverLeave
• src/mixed-line-bar-chart/__tests__/use-mouse-hover.test.ts — Updated and added tests for both changes

Before:

Bildschirmaufnahme.2026-03-13.um.15.18.11.mov

After:

Bildschirmaufnahme.2026-03-13.um.15.18.31.mov

Related links, issue #, if available: n/a

How has this been tested?

Review checklist

The following items are to be evaluated by the author(s) and the reviewer(s).

Correctness

• Changes include appropriate documentation updates.
• Changes are backward-compatible if not indicated, see CONTRIBUTING.md.
• Changes do not include unsupported browser features, see CONTRIBUTING.md.
• Changes were manually tested for accessibility, see accessibility guidelines.

Security

• If the code handles URLs: all URLs are validated through the checkSafeUrl function.

Testing

• Changes are covered with new/existing unit tests?
• Changes are covered with new/existing integration tests?

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.43%. Comparing base (302fd0e) to head (4b1878d).
⚠️ Report is 10 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4350      +/-   ##
==========================================
- Coverage   97.44%   97.43%   -0.01%     
==========================================
  Files         897      901       +4     
  Lines       26395    26454      +59     
  Branches     9525     9531       +6     
==========================================
+ Hits        25721    25776      +55     
- Misses        668      672       +4     
  Partials        6        6              

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