File not found when running `quarto preview --to pdf` on a large book

[kusnezoff-alexander]

I have:

• searched the issue tracker for similar issues
• installed the latest version of Quarto CLI
• formatted my issue following the Bug Reports guide

Bug description

I am currently using Quarto books to write a thesis. Using quarto preview --to pdf the first time does indeed work, but whenever I make changes to any .qmd file the pdf gets recompiled causing the error: /web/<book-title>.pdf (404: Not Found).

My feeling is that there is a race condition somewhere since modifying my thesis (eg deleting whole chapters, reducing the overall compilation time) solve the problem.

Steps to reproduce

See https://github.com/kusnezoff-alexander/quarto-preview-to-pdf-error

Actual behavior

Output when running quarto preview --to pdf for the first time:

❯ quarto preview --to pdf
Preparing to preview
[ 1/13] index.qmd
[ 2/13] content/Background/index.qmd
<...other files..>

pandoc 
  to: latex
  from: markdown+emoji
  output-file: index.tex
  template: template.tex
  standalone: true
  toc: true
  number-sections: true
  top-level-division: chapter
  pdf-engine: lualatex
  variables:
    graphics: true
    tables: true
  default-image-extension: pdf
  
metadata
  crossref:
    chapters: true
  documentclass: scrreprt
  papersize: letter
  block-headings: true
  lst-cap-location: bottom
  fig-cap-location: bottom
  tbl-cap-location: bottom
  csl: ieee.csl
  <some_more_metadata>
  
BEWARE: your OS is not officially supported by Playwright; downloading fallback build for u
buntu20.04-x64.
BEWARE: your OS is not officially supported by Playwright; downloading fallback build for u
buntu20.04-x64.
success: successfully compiled /tmp/d2-render-b2d8687da58196d4/diagram-1.d2 to _book/diagra
m-1.pdf in 2.046727481s
BEWARE: your OS is not officially supported by Playwright; downloading fallback build for u
buntu20.04-x64.
BEWARE: your OS is not officially supported by Playwright; downloading fallback build for u
buntu20.04-x64.
success: successfully compiled /tmp/d2-render-d1ee1fc8de98a171/diagram-2.d2 to _book/diagra
m-2.pdf in 2.156744879s
WARNING (/opt/quarto-1.8.25/share/filters/main.lua:22344) FloatRefTarget with no content: f
ig-code_cim

Rendering PDF
running lualatex - 1
  This is LuaHBTeX, Version 1.17.0 (TeX Live 2023) 
   restricted system commands enabled.
  
running lualatex - 2
  This is LuaHBTeX, Version 1.17.0 (TeX Live 2023) 
   restricted system commands enabled.
  
running lualatex - 3
  This is LuaHBTeX, Version 1.17.0 (TeX Live 2023) 
   restricted system commands enabled.

Watching files for changes
Browse at http://localhost:7834/web/viewer.html
Listening on http://127.0.0.1:7834/
Opening in existing browser session.
GET: /web/viewer.html

Console output when doing any changes (causing the pdf to recompile):

[ 1/13] index.qmd
[ 2/13] content/Background/index.qmd
<...more files...>
pandoc 
  to: latex
  from: markdown+emoji
  output-file: index.tex
  template: template.tex
  standalone: true
  toc: true
  number-sections: true
  top-level-division: chapter
  pdf-engine: lualatex
  variables:
    graphics: true
    tables: true
  default-image-extension: pdf
  
metadata
  crossref:
    chapters: true
  documentclass: scrreprt
  papersize: letter
  block-headings: true
  lst-cap-location: bottom
  fig-cap-location: bottom
  tbl-cap-location: bottom
  csl: ieee.csl
  <some-more-metadata>
  
BEWARE: your OS is not officially supported by Playwright; downloading fallback build for u
buntu20.04-x64.
BEWARE: your OS is not officially supported by Playwright; downloading fallback build for u
buntu20.04-x64.
success: successfully compiled /tmp/d2-render-22d1ec558ef64c7f/diagram-1.d2 to _book/diagra
m-1.pdf in 2.017175096s
BEWARE: your OS is not officially supported by Playwright; downloading fallback build for u
buntu20.04-x64.
BEWARE: your OS is not officially supported by Playwright; downloading fallback build for u
buntu20.04-x64.
success: successfully compiled /tmp/d2-render-8e96caa0edb1dee6/diagram-2.d2 to _book/diagra
m-2.pdf in 2.030154504s
WARNING (/opt/quarto-1.8.25/share/filters/main.lua:22344) FloatRefTarget with no content: f
ig-code_cim

Rendering PDF
running lualatex - 1
  This is LuaHBTeX, Version 1.17.0 (TeX Live 2023) 
   restricted system commands enabled.
  
running lualatex - 2
  This is LuaHBTeX, Version 1.17.0 (TeX Live 2023) 
   restricted system commands enabled.
  
running lualatex - 3
  This is LuaHBTeX, Version 1.17.0 (TeX Live 2023) 
   restricted system commands enabled.
  

GET: /web/viewer.html
[ 1/13] index.qmd
[ 2/13] content/Background/index.qmd
[ 3/13] content/Title1.qmd
[ 4/13] content/Title2.qmd
  /web/<book-title>.pdf (404: Not Found)

and then it gets caught in an endless loop where it tries to recompile the pdf and saying the book pdf can't be found (_book/ is also empty)

Expected behavior

quarto preview --to pdf recompiles successfully when doing changes to my book

Your environment

• nvim: NVIM v0.11.4
• OS: Fedora42

Quarto check output

❯ quarto check
Quarto 1.8.25
[✓] Checking environment information...
      Quarto cache location: /home/alex/.cache/quarto
[✓] Checking versions of quarto binary dependencies...
      Pandoc version 3.6.3: OK
      Dart Sass version 1.87.0: OK
      Deno version 2.3.1: OK
      Typst version 0.13.0: OK
[✓] Checking versions of quarto dependencies......OK
[✓] Checking Quarto installation......OK
      Version: 1.8.25
      Path: /opt/quarto-1.8.25/bin

[✓] Checking tools....................OK
      Chromium: 869685
      TinyTeX: (not installed)

[✓] Checking LaTeX....................OK
      Using: Installation From Path
      Path: /usr/bin
      Version: 2023

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

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

[✓] Checking Python 3 installation....OK
      Version: 3.13.9
      Path: /usr/bin/python3
      Jupyter: 5.7.2
      Kernels: .venv, myenv, python3, rust

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

[✓] Checking R installation...........OK
      Version: 4.5.1
      Path: /usr/lib64/R
      LibPaths:
        - /home/alex/R/x86_64-redhat-linux-gnu-library/4.5
        - /usr/lib64/R/library
        - /usr/share/R/library
      knitr: 1.45
      rmarkdown: 2.24

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

[cderv]

I needed to solve some related problem due to missing fonts not found so that I can try reproduce. Hence the PR linked

[cderv]

Thanks for the detailed report! I've been investigating this issue and can now reproduce it with a minimal example.

Minimal Reproducible Case

The issue occurs specifically when:

• A book project has mermaid diagrams
• The .qmd file is in a nested directory (e.g., content/mermaid.qmd)

Reproduces consistently:

# _quarto.yml
project:
  type: book

book:
  title: "My Thesis"
  chapters:
    - index.qmd
    - content/mermaid.qmd  # ← mermaid cells here trigger the issue

Does NOT reproduce:

• When mermaid cells are removed from the file
• When the file is moved to root directory (mermaid.qmd instead of content/mermaid.qmd)

Probable Cause

Based on the reproducibility pattern, this appears to be related to how the file watcher handles output artifacts:

During rendering, mermaid creates output files in the source directory (e.g., content/mermaid_files/figure-latex/*.svg). The file watcher may be detecting these newly created files as changes, which could trigger another render cycle while the previous render is still completing. When the browser then requests the PDF, it's not ready yet → 404 error.

The nested directory structure might make this timing issue more pronounced (more file operations, deeper paths), making it easier to hit the condition.

This could potentially affect other diagram handlers that create *_files/ directories in the source tree (plotly, d2, htmlwidgets, etc.), though I've only confirmed it with mermaid so far.

Investigating a fix now.

[kusnezoff-alexander]

@cderv Hey, just wanted to ask whether there are any updates on this? Thanks for looking into the issue.

[mcanouil]

@cderv Hey, just wanted to ask whether there are any updates on this? Thanks for looking into the issue.

@kusnezoff-alexander

We appreciate your interest in the project, but I'd like to share some guidance on how we can make discussions more productive.

Posts asking "Any news?" or "When will this be ready?" without specific questions or constructive feedback don't help move development forward.
They create notification noise for maintainers without providing actionable input that could influence development priorities.

Rather than asking for general updates, consider asking specific technical questions about implementation, contributing implementation suggestions, or submitting pull requests for features you need.
Consider upvoting and/or adding a "thumb up" on the original message.

The most valuable contributions focus on "here's how I can help solve this" rather than "here's what I want you to do for me."

For the latest information about progress and planned features, check the project's changelog, release notes, or issues.

Thanks for understanding and for your continued interest in the project.