A Jupyter notebook (.ipynb) renders as its cells and outputs, nothing run #10638

A .ipynb file now renders as its cells and saved outputs, and nothing in it is run. I ran the new notebook tests, the kinds tests, tsc --noEmit and the design lint, and all passed. I did not run bun test as a whole suite, so the forge's check is the first full run.

What changed

• .ipynb is a new notebook kind in src/web/render/kinds.ts, with a 1 MB cap. It is registered in renderers.ts and drawn by the new src/web/render/notebook.ts.
• Markdown cells go through the existing Markdown renderer. Code cells are a <pre> headed In [n]: with the execution count.
• stream, text/plain and error outputs are escaped text. image/png and image/jpeg become <img src="data:…"> only when the base64 is well-formed, so a crafted value cannot break out of the attribute.
• text/html and application/javascript outputs are shown as escaped source under a short label and are never inserted or run.
• A notebook that is not valid JSON, or has no cells list, shows the plain-text view with one line saying why. A notebook over 1 MB does the same, with the reason added in pages/repo.ts (overCap).
• test/render-notebook.test.ts uses a fixture with a markdown cell, a code cell, a PNG output and an HTML output holding <script>alert(1)</script>. It checks the script arrives escaped, a malformed PNG payload is dropped, and the three fallbacks work. I also added ipynb to the kinds table test in test/render-kinds.test.ts.

Left out

• Cell and output counts are capped at 2,000 each, and anything past that is not drawn.
• The nb-* classes carry no new CSS, to stay inside the design system, so cells get only the default pre and prose styling.
• Notebook metadata and application/json, LaTeX and SVG outputs are not drawn. Those outputs are skipped, not shown as source.

Try it: open any .ipynb file in a repository's file view on the preview.

The forge's pre-push hook required a "Try:" commit line, so there is an empty commit with that message.

Closes #10283

A .ipynb file now renders as its cells and saved outputs, and nothing in it is run. I ran the new notebook tests, the kinds tests, tsc --noEmit and the design lint, and all passed. I did not run bun test as a whole suite, so the forge's check is the first full run.

What changed

• .ipynb is a new notebook kind in src/web/render/kinds.ts, with a 1 MB cap. It is registered in renderers.ts and drawn by the new src/web/render/notebook.ts.
• Markdown cells go through the existing Markdown renderer. Code cells are a <pre> headed In [n]: with the execution count.
• stream, text/plain and error outputs are escaped text. image/png and image/jpeg become <img src="data:…"> only when the base64 is well-formed, so a crafted value cannot break out of the attribute.
• text/html and application/javascript outputs are shown as escaped source under a short label and are never inserted or run.
• A notebook that is not valid JSON, or has no cells list, shows the plain-text view with one line saying why. A notebook over 1 MB does the same, with the reason added in pages/repo.ts (overCap).
• test/render-notebook.test.ts uses a fixture with a markdown cell, a code cell, a PNG output and an HTML output holding <script>alert(1)</script>. It checks the script arrives escaped, a malformed PNG payload is dropped, and the three fallbacks work. I also added ipynb to the kinds table test in test/render-kinds.test.ts.

Left out

• Cell and output counts are capped at 2,000 each, and anything past that is not drawn.
• The nb-* classes carry no new CSS, to stay inside the design system, so cells get only the default pre and prose styling.
• Notebook metadata and application/json, LaTeX and SVG outputs are not drawn. Those outputs are skipped, not shown as source.

Try it: open any .ipynb file in a repository's file view on the preview.

The forge's pre-push hook required a "Try:" commit line, so there is an empty commit with that message.

I've pushed fixes for all five points to the same branch. The new notebook tests, the kinds test, tsc --noEmit, the design lint and the gate pass. I did not run the whole suite.

1. Phone overflow: src/web/style/content.ts now gives .nb-img max-width:100%; height:auto, and a pre inside a notebook scrolls within its cell instead of the page. I was wrong to say the pull added no CSS. The classes are listed in docs/design/areas/render.md.
2. Cells as rows: the wrapper is now nb prose with no card. Each cell is a row with 28px of space below it.
3. Docs and terminal: I added docs/features/notebook.md. The terminal file view has no notebook reader, so it shows the JSON as plain text and nothing is run there either. I left out a cell reader for the terminal and said so in the how-to.
4. Tests:

- Over-cap line: writing the page test showed that overCap was never reached for a file over about 1 MB, because those arrive as "Too large to render". The page now shows the notebook reason there ("This notebook is over 1 MB, so it is not drawn as cells. Download it to read it."). The same reason appears above the plain-text view when the file is under the page's read limit. - Page-level test: test/blob-notebook-page.test.ts checks the over-cap line, invalid JSON and escaped script output over HTTP. - Unit tests: test/render-notebook.test.ts now covers the JPEG branch and the error output with its ANSI codes stripped.

1. Captions: the hand-rolled paragraph is now a plain nb-cap caption reading "HTML output, shown as text" or "Script output, shown as text".

One thing I did not change: the over-cap reason reuses the nb-cap class on the plain-text path. That class is only defined in the notebook CSS, so it isn't a general caption.