Open the help in the down area (pager)

[jtpio]

Fixes #6692
Fixes #1135

To offer a behavior similar to the classic notebook:

notebook-down-pager.mp4

The idea would be to have this behavior by default in Notebook 7.5, with a setting to disable it and have the pager data be displayed in the cell output like in JupyterLab:

notebook-pager-disabled.mp4

Example with xeus-cpp showing a text/html bundle:

notebook-xeus-cpp-pager.mp4

• Open the pager in the down area
• Setting to disable this behavior and default to the JupyterLab behavior
• If disabled, allow opening the "Contextual Help" and click around like in JupyterLab
• UI test
• Update snapshots
• Docs

[github-actions]

👈 Launch a Binder on branch jtpio/notebook/down-pager

[jtpio]

So, I think this PR should be ready for a first round of reviews.

As a quick summary, it brings back the behavior of the pager just like the classic notebook. This has been missing since the early Jupyter Notebook 7 releases (released a bit more than two years ago), and there's been some feedback that this was still missing.

I've also added some UI tests to cover some cases, and also added a new page in the docs so that folks can opt out of this new behavior and return to the JupyterLab behavior if they want to.

If folks would like to try it, that would be great, let me know what you think. I'm also happy to iterate on a different approach if you think the current one could be improved.

[Copilot]

Pull Request Overview

This PR implements a pager widget that displays help documentation in the down area (inspector panel) similar to classic notebook behavior, providing an alternative to JupyterLab's inline output approach. Users can toggle this behavior through settings to maintain compatibility with either classic notebook or JupyterLab workflows.

• Implements a new pager plugin that intercepts kernel messages with pager payloads and displays them in the inspector panel
• Adds configuration option to switch between down-area display and inline cell output behavior
• Updates shell layout to support inspector placement in the down area

Reviewed Changes

Copilot reviewed 9 out of 13 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
packages/notebook-extension/src/index.ts	Core pager plugin implementation with kernel message handling and inspector integration
packages/notebook-extension/schema/pager.json	Settings schema for configuring pager behavior
packages/notebook-extension/package.json	Added inspector dependency
packages/application/src/shell.ts	Enhanced down panel activation to support tab switching
packages/application-extension/schema/shell.json	Updated shell configuration to place Inspector in down area by default
ui-tests/test/notebook.spec.ts	Added test to verify pager opens in down area with question mark syntax
docs/source/user-documentation.md	Added pager documentation reference
docs/source/pager.md	Complete user documentation for pager functionality
app/package.json	Added inspector extension dependencies and configuration

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