Only remount a plot when its payload changes

[hysts]

Description

A gr.Plot inside a gr.Chatbot message was torn down and rebuilt on every streaming update of the chat history. With a bokeh plot that shows up as flickering and as the view flipping between the top and the bottom of the conversation while the reply streams: re-embedding clears the container, so the message height collapses to 0 and grows back on every update. It does land at the bottom once the reply finishes, but everything in between is unusable.

js/plot/shared/Plot.svelte wraps the plot in {#key key} and its $effect incremented key on every run. The effect depends on the value prop, and gr.Chatbot rebuilds its message objects on every update, so value arrived as a fresh object holding the same payload roughly 30 times per streamed reply and each one forced a full remount.

The remount is deliberate (added in #9781 so a plot change renders cleanly), so this keeps it and only gates it: key now advances when the payload changes (type, plot, or altair's chart) rather than when the prop's object identity changes. PlotData is fully described by those fields, and the plot type components already track value in place through $derived, so nothing else had to move.

Measured with the issue's app on a bokeh plot, over one plain-text turn (31 streaming yields) after the plot was displayed:

	plot remounts	max distance from bottom
before	33	493 px
after	0	26 px (transient, ends at 0)

Plotly and matplotlib also went from 33 remounts to 0. They kept their height across the remount, so they never showed the scroll jump, only the wasted re-render.

Closes: #10107

Testing

Two tests in js/plot/Plot.test.ts: an unchanged payload delivered as a new object keeps the same plot element, and a changed payload still replaces it (that second one guards #9781's remount). The first test fails on main and passes with this change.

The rest of the frontend unit suite passes locally (77 files, 2137 tests), as do the chatbot tests.

gr.Plot renders through only two paths, standalone via js/plot/Index.svelte and inside the chatbot via js/chatbot/shared/Component.svelte, and both are covered above. Standalone plots see no behaviour change beyond skipping a redundant re-render when the backend re-sends an identical plot. The change event still fires exactly as before; it was never tied to the remount.

Two things this deliberately leaves alone. The chatbot's autoscroll still uses a fixed tick() + 300 ms timeout, which is fine once the plot stops collapsing its height (the 26 px above is normal lag while content grows). And a wide bokeh figure still overflows the chat bubble, which hannahblair noted on the issue; that is a layout question separate from the scroll reset.

Before / after Spaces

Same app on both, so the only difference is which gradio it installs. Send plot, then send anything else and watch the chat area while the reply streams.

• Before fix (released 6.20.0)
• After fix (preview wheel for this PR)

Driving both with the same Playwright probe: 80 plot remounts and up to 600 px away from the bottom on the before Space, 0 remounts and 26 px on the after Space.

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[gradio-pr-bot]

🪼 branch checks and previews

•	Name	Status	URL
	Spaces	ready!	Spaces preview
	Storybook	ready!	Storybook preview
🦄	Changes	detected!	Details

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Install Gradio from this PR

pip install https://huggingface.co/buckets/gradio/pypi-previews/resolve/85456576c9a5ff442ab11210607bfceede1fb77b/gradio-6.20.0-py3-none-any.whl

Install Gradio Python Client from this PR

pip install "gradio-client @ git+https://github.com/gradio-app/gradio@85456576c9a5ff442ab11210607bfceede1fb77b#subdirectory=client/python"

Import Gradio JS Client from this PR via CDN

import { Client } from "https://huggingface.co/buckets/gradio/npm-previews/resolve/85456576c9a5ff442ab11210607bfceede1fb77b/browser.js";

[gradio-pr-bot]

🦄 change detected

This Pull Request includes changes to the following packages.

Package	Version
@gradio/plot	patch
gradio	patch

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• Only remount a plot when its payload changes

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[Copilot]

Pull request overview

This PR fixes a Gradio frontend regression where plots embedded in gr.Chatbot messages were being unnecessarily remounted during streaming updates, causing visible flicker and scroll jumping (notably with Bokeh). It keeps the intentional “remount on plot change” behavior (added for cleaner plot updates) but gates it so remounts only occur when the plot payload meaningfully changes.

Changes:

• Updates js/plot/shared/Plot.svelte to advance the {#key ...} remount key only when the plot payload (type, plot, or Altair’s chart) changes, rather than whenever the value prop’s object identity changes.
• Adds regression tests ensuring identical payloads delivered via new objects do not remount, while genuine payload changes still do remount.

Reviewed changes

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

File	Description
js/plot/shared/Plot.svelte	Prevents unnecessary plot remounts by comparing payload fields instead of prop identity, avoiding flicker/scroll jumps during chatbot streaming.
js/plot/Plot.test.ts	Adds targeted tests to prevent regressions: no remount for unchanged payloads, but remount preserved for actual payload changes.

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