Use `post-render` only when `quarto render` is used

Discussed in https://github.com/quarto-dev/quarto-cli/discussions/10310

^{Originally posted by skwde July 17, 2024}

Description

Currently there is no way (at least to my basic knowledge) to run post-render only when quarto render is used.

Consider following case:
When explicitly calling quarto render revealjs-slides.qmd I want to run a post-render step calling decktape to convert the slides to pdf.
In particular it should not run when I use quarto preview revealjs-slides.qmd.

The discussion https://github.com/quarto-dev/quarto-cli/discussions/6080 mentions the use of QUARTO_PROJECT_RENDER_ALL but this does not work if there are other .qmd files in the project.

Here is a working example.

We have the _quarto.yml

project:
  post-render:
    - test.sh

and the test.sh

#!/usr/bin/env bash

echo "Variables:"
echo ${QUARTO_PROJECT_RENDER_ALL}
echo ${QUARTO_PROJECT_OUTPUT_DIR}
echo ${QUARTO_PROJECT_INPUT_FILES}
echo ${QUARTO_PROJECT_OUTPUT_FILES}

Following test.qmd is used

---
format: revealjs
---

# Test

abc

In addition there is an empty another.qmd.
Running both render and preview on test.qmd shows that the post-render is executed

quarto render test.qmd
quarto preview test.qmd

Maybe another variable QUARTO_PREVIEW would be helpful here.

I use Quarto version 1.5.54 in a devcontainer running debian bookworm.