Describe your changes

Vega-Lite/Altair charts that size via autosize: pad (facet charts and nested compositions like vconcat + hconcat) render an SVG whose total width is driven by the plotting area plus axes, facet panels, and padding. Vega-Lite's width only controls the plotting area, so the rendered SVG can be wider than its wrapper. In a narrow st.columns cell the chart then spilled out of its column/card and overlapped neighboring elements.

Clip the rendered chart to the wrapper bounds (max-width: 100% + overflow: hidden) only for these pad-sized charts. Simple fit/fit-x charts already match the wrapper exactly, so they are left untouched — clipping them would crop edge axis labels and is unnecessary.

• Clipping is gated on isFacet || hasNestedComp, the same conditions the backend uses to choose autosize: pad.
• The chart action menu is a sibling of .chart-wrapper, so it is not affected by the clip.

Screenshot or video (only for visual changes)

Faceted line charts inside cards in narrow columns.

Before (charts overflow and overlap neighboring cards):

Before fix - facet charts overflow narrow columns

After (charts are clipped to their card bounds):

After fix - facet charts clipped to card bounds

GitHub Issue Link (if applicable)

N/A

Testing Plan

• E2E Tests: existing st_vega_lite_chart_test.py and st_vega_charts_height_test.py pass unchanged. In st_vega_charts_width_test.py the facet/nested charts share a page with simple charts; clipping the faceted charts produces an imperceptible (~1.8%) sub-pixel shift of the sibling simple charts on that page, so the four affected width snapshots (width_content[chromium], width_content/width_stretch/width_400px[firefox]) were regenerated. Local Linux rendering reproduced CI's pixel diffs exactly; webkit/chromium-stretch/400px were unaffected.
• Frontend unit tests: existing ArrowVegaLiteChart suite passes (127 tests).
• Manual testing: verified with Playwright screenshots at 1280px and 760px viewports that faceted charts no longer overflow narrow columns while simple charts and full-width charts are unaffected.

Contribution License Agreement

By submitting this pull request you agree that all contributions to this project are made under the Apache 2.0 license.

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