References

• Same idea as Freeze size of heavy nodes when resizing panels lumino#812
• Addresses Resizing of panels is slow when there are many nodes in resized notebooks/widgets lumino#505 but for now in JupyterLab rather than lumino

This will allow us to get feedback on this change during the beta cycle, without having to commit to extended API surface in lumino yet.

Code changes

• Adds optimizeResize Shell setting
• Adds OptimizedDockPanelSvg subclass of DockPanelSvg
• Uses OptimizedDockPanelSvg in the LabShell

User-facing changes

Resizing is faster. This can be verified by running:

BENCHMARK_NUMBER_SAMPLES=20 jlpm test:benchmark --grep "Notebook Resize"

import json, statistics
data = json.load(open('~/jupyterlab/galata/benchmark-results/lab-benchmark.json'))
by_mode = {}
for r in data['values']:
    by_mode.setdefault(r['file'], []).append(r['time'])

for name, times in sorted(by_mode.items()):
    n = len(times)
    avg = sum(times)/n
    med = statistics.median(times)
    sd = statistics.stdev(times)
    print(f'{name}: n={n}  avg={avg:.0f}ms  median={med:.0f}ms  sd={sd:.0f}ms  min={min(times):.0f}ms  max={max(times):.0f}ms')

Before

After

Backwards-incompatible changes

None

AI usage

• Yes: Some or all of the content of this PR was generated by AI.
• Yes: The human author has carefully reviewed this PR and run this code (keep this PR "draft" until the answer is YES)
• AI tools and models used: Claude Code, Codex