User/mattwar/large data charts

[mattwar]

Speed up chart rendering and resize for large result sets

A 50,000-row chart used to take minutes and was unresponsive to resize/edit. After this PR, it renders in a couple of seconds and resizes cleanly.

Changes

• WebGL traces: line/scatter/non-stacked-area traces with >1000 points now use Plotly scattergl instead of SVG scatter.
• Faster page parse: chart data is embedded as JSON.parse('…') instead of a JavaScript object literal.
• Structured payload: single-chart renders post {divId, dataJson, layoutJson, configJson} and the page calls Plotly.newPlot directly, avoiding a multi-MB innerHTML parse and script reinjection.
• Skip sort when sorted: trace builder detects monotonic-x input and reuses the arrays in place.
• Cheaper resize: Plotly.relayout (layout-only) replaces Plotly.newPlot on resize, eliminating GPU re-upload.
• No double-resize: fill-mode wrapper is now absolutely positioned so its layout can't retrigger the ResizeObserver.
• Faster resize trigger: requestAnimationFrame replaces setTimeout(50) after panel toggle / view switch.
• Layout helper cleanup: dark/light helpers mutate the in-memory layout object instead of round-tripping through JSON.

Follow-up fixes from PR feedback

• Escape U+2028 / U+2029 in embedded JSON so the generated <script> is valid on any runtime.
• Apply fill-mode wrapper isolation in _chartUpdated too, so the initial render can't trigger the same ResizeObserver feedback loop the resize path was already protected against.
• Add a chartViewReady handshake so setChartContent is reliably delivered on initial load and after webview.html rebuilds, with the latest payload cached in PlotlyChartView for replay.
• Harden the setChartContent handler against untrusted postMessage payloads: validate divId against a strict pattern and build the placeholder element via createElement/appendChild instead of innerHTML concatenation.
• Sync the test helper's local escape and decodeJsStringLiteral with the production escapeForJsStringLiteral so the structured-invoke path round-trips correctly for U+2028 / U+2029.

Tests

All 112 unit tests pass; added cases for the scattergl threshold (and that stacked area stays on SVG), the monotonic-x fast path, and the new structured setChartContent invocation.

[Copilot]

Pull request overview

This PR improves Plotly chart responsiveness for large result sets in the VS Code results viewer by reducing DOM-heavy SVG rendering, avoiding expensive HTML/script reinjection, and making resizes/layout updates cheaper.

Changes:

• Switches large line/scatter/non-stacked-area traces to WebGL (scattergl) above a point threshold.
• Introduces structured single-chart rendering via postMessage payloads ({ divId, dataJson, layoutJson, configJson }) and faster JSON embedding (JSON.parse('...')) for HTML-based paths.
• Optimizes resize behavior (uses Plotly.relayout, wrapper positioning, rAF resize trigger) and skips sorting when x is already monotonic.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 4 comments.

File	Description
src/Client/tests/unit/plotlyChartProvider.test.ts	Updates tests for structured setChartContent rendering and adds coverage for scattergl threshold + monotonic-x fast path.
src/Client/features/resultsViewer.ts	Adjusts chart container CSS to prevent ResizeObserver loops and uses requestAnimationFrame for resize triggering on view/panel toggles.
src/Client/features/plotlyChartProvider.ts	Implements WebGL trace selection, structured single-chart payload rendering, faster JSON embedding, monotonic-x sort skip, and relayout-based resize updates.

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[Copilot]

_chartUpdated() still uses the non–aspect-ratio branch that clears wrapperDiv.style.position/left/top (see just above this block), while resizeChartCore() now relies on the wrapper being absolutely positioned in fill mode to prevent ResizeObserver feedback loops. Consider updating _chartUpdated() to apply the same fill-mode wrapper positioning (absolute + left/top = 0) so a post-update layout change doesn’t immediately retrigger an extra resize.