Wrong title in html formats in presence of Jupyter code block & with _metadata.yml

Bug description

I believe I might continue to observe a variation of the (currently closed) issue #6411 with Quarto 1.7.27.

My problem is essentially the same as described there: for HTML output formats (html, revealjs), the first section heading will be interpreted as the document title despite a document title: being specified in the metadata, but only if a code block rendered by the Jupyter engine is present (but for Knitr, the problem does not occur).

Issue #6411 has been closed, and in an MWE there, where the document title: was specified in _quarto.yml, the problem is indeed resolved. However, I continue to observe the same symptoms if the document title: is specified not in _quarto.yml, but _metadata.yml.

Steps to reproduce

Issue #6411 is indeed resolved in the following MWE provided by @cderv, as the release notes for v1.4 suggest:

_quarto.yml:

title: "My title"
author: "John Doe"

format: html

index.qmd:

## First slide heading

Some content

```{python}
1 + 1
```

If I render this MWE with

quarto render index.qmd --to html

the expected title: value from _quarto.yml is being used as the document title. Render command output:

Starting python3 kernel...Done

Executing 'index.quarto_ipynb'
  Cell 1/1: ''...Done

pandoc 
  to: html
  output-file: index.html
  standalone: true
  section-divs: true
  html-math-method: mathjax
  wrap: none
  default-image-extension: png
  variables: {}
  
metadata
  document-css: false
  link-citations: true
  date-format: long
  lang: en
  title: My title
  author: John Doe
  
Output created: index.html

However, in that same MWE, if I simply

mv _quarto.yml _metadata.yml

and re-render via

quarto render index.qmd --to html

the original issue described in #6411 re-appears again, i.e., the first section heading becomes the document title. Re-render output:

Starting python3 kernel...Done

Executing 'index.quarto_ipynb'
  Cell 1/1: ''...Done

pandoc 
  to: html
  output-file: index.html
  standalone: true
  section-divs: true
  html-math-method: mathjax
  wrap: none
  default-image-extension: png
  variables: {}
  
metadata
  document-css: false
  link-citations: true
  date-format: long
  lang: en
  title: My title
  author: John Doe
  
Output created: index.html

If I then delete the Python code block from index.qmd and re-render, the issue disappears once more, i.e., the expected document title from the .yml file is being used. This seems consistent with the diagnosis in the original issue, i.e., that the issue occurs only with the Jupyter, but not the Knitr engine.

I am guessing this behavior is not by design?

Actual behavior

The first section heading is used as the document title, despite the presence of document title: metadata in _metadata.yml.

Expected behavior

The title: field in _metadata.yml should be honored as the document's title.

Your environment

• IDE: vim, bash, Makefile
• OS: Debian testing

Quarto check output

Quarto 1.7.27
[✓] Checking environment information...
      Quarto cache location: /home/flo/.cache/quarto
[✓] Checking versions of quarto binary dependencies...
      Pandoc version 3.6.3: OK
      Dart Sass version 1.85.1: OK
      Deno version 1.46.3: OK
      Typst version 0.13.0: OK
[✓] Checking versions of quarto dependencies......OK
[✓] Checking Quarto installation......OK
      Version: 1.7.27
      Path: /opt/quarto/bin

[✓] Checking tools....................OK
      TinyTeX: (not installed)
      Chromium: (not installed)

[✓] Checking LaTeX....................OK
      Using: Installation From Path
      Path: /usr/bin
      Version: 2025

[✓] Checking Chrome Headless....................OK
      Using: Chrome found on system
      Path: /usr/bin/google-chrome
      Source: PATH

[✓] Checking basic markdown render....OK

[✓] Checking Python 3 installation....OK
      Version: 3.13.3
      Path: /usr/bin/python3
      Jupyter: 5.7.2
      Kernels: python3

[✓] Checking Jupyter engine render....OK

[✓] Checking R installation...........OK
      Version: 4.4.3
      Path: /usr/lib/R
      LibPaths:
        - /home/flo/R/x86_64-pc-linux-gnu-library/4.4
        - /usr/local/lib/R/site-library
        - /usr/lib/R/site-library
        - /usr/lib/R/library
      knitr: 1.50
      rmarkdown: 2.29

[✓] Checking Knitr engine render......OK