Fix multiline tooltip clipping

[jacobvjk]

Summary

• Fixed tooltip clipping in MultiLineChart: the hover tooltip now repositions near the plot's edges instead of overflowing past them. It slides horizontally to stay within the left/right margins, and flips above the point when there is not enough space below. This mirrors the fix already shipped for NormalizedStackedAreaChart in Feat tooltip stacked area chart #909.
• Tail always points at the exact hovered data point, even when the box has shifted or flipped to fit.
• Extracted the positioning math into a pure, reusable function (chartTooltipLayout.ts) to make it testable without an SVG layout engine.
• Added unit tests (chartTooltipLayout.test.ts) covering the following cases:
  • default/centered case
  • left/right edge sliding
  • bottom-edge flip
  • a corner case (both axes at once)
  • and two fallback edge cases.

Related issues

Closes: #910

Testing

• added new unit tests making use of the repositioning math to ensure the tooltip stays within bounds in all relevant cases
• manually validated the functionality

Checklist

• PR is focused on a single concern
• Tests pass locally and in CI
• Docs updated for user-visible changes
• AI-assisted portions declared (see CONTRIBUTING.md)

[github-actions]

Expected version change and release notes:

1.16.0-dev.16 (v1.16.0-dev.15...fix-multiline-tooltip-clipping ) (2026-08-19T12:35 UTC)

Fixes

• no more clipping of tooltip (3dc8b64)

[github-actions]

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[Copilot]

Pull request overview

This PR addresses tooltip clipping in MultiLineChart by introducing reusable, unit-testable tooltip positioning geometry and applying it to the chart’s per-point hover tooltip so it stays within plot bounds while keeping the tail anchored to the hovered point.

Changes:

• Added a pure computeTooltipBoxLayout utility to compute clamped/flip tooltip box geometry within plot bounds.
• Updated MultiLineChart to use the new layout function for tooltip path/text positioning (including edge sliding and vertical flipping).
• Added Vitest unit tests covering centered, edge, flip, corner, and fallback behaviors for the layout utility.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
src/utils/chartTooltipLayout.ts	New pure geometry helper for computing tooltip box/tail layout within plot bounds
src/utils/chartTooltipLayout.test.ts	Unit tests for tooltip layout behavior across edge and fallback cases
src/components/MultiLineChart.tsx	Integrates computed tooltip layout to prevent clipping and keep tail anchored to the hovered point

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[github-actions]

Azure Static Web Apps: Your stage site is ready! Visit it here: https://proud-glacier-0f640931e-913.westus2.2.azurestaticapps.net

[Copilot]

Pull request overview

Copilot reviewed 3 out of 3 changed files in this pull request and generated no new comments.