Fix quarto inspect standalone file project emission for RStudio

[cderv]

When publishing a standalone Quarto document from RStudio's publishing wizard with Quarto >= 1.9.35, the wizard crashes with "missing value where TRUE/FALSE needed".

Root Cause

Commit f6a0f89 (v1.9.35, fix for #14208) moved result.config = result.config || { project: {} } outside the if (renderOptions) block in singleFileProjectContext so Julia engine extensions resolve correctly during preview. Side effect: context.config is now always truthy for standalone files, so inspectDocumentConfig emits a project field with dir set to the file's parent directory.

RStudio's C++ bridge (SessionQuarto.cpp) reads project.dir from quarto inspect output and assumes _quarto.yml exists there. It adds the config file to the deploy list, file.info() returns NA for the non-existent file, and the size comparison crashes.

Fix

Gate project emission in inspectDocumentConfig on !(isSingleFile && isRStudio()). This preserves the "everything is a project" direction for non-RStudio consumers while maintaining compatibility with current RStudio releases.

Alternative Considered

Unconditionally suppressing project for all single-file contexts (!context.isSingleFile) would also fix the issue without RStudio detection. However, single-file projects are intentional internal behavior and other consumers may rely on the project metadata. The RStudio-specific gate is more targeted.

The RStudio-side fix is in rstudio/rstudio#17336 (merged) but will not be backported to older releases. This Quarto-side workaround protects users on older RStudio versions that upgrade Quarto independently.

Also adds _setIsRStudioForTest() override in platform.ts to avoid Deno.env.set() race conditions in parallel tests (#14218).

Test Plan

• quarto inspect standalone.qmd with RStudio override: no project field in output
• quarto inspect standalone.qmd without override: project field present with dir
• Existing inspect tests pass (extensions, includes, code-cells, cleanup)

Ref: rstudio/rstudio#17333

[cderv]

@cscheid is that what you add in mind as a fix ?

I wanted to try gate this for RStudio Version, but I don't think it can be accessed easily unfortunately. So I just have a scoped build to hide project from inspect in rstudio.

But maybe you want to remove singleFile project info from inspect in all cases ?

I hesitated doing this, so happy to get your thought.

Also I have made the backport so current release 1.9 works in existing and old RStudio IDE