strange behavior when toc-location is left

Bug description

i'm not sure if some of this behavior is intentional, but it seemed a bit odd to me.

i have a quarto website where toc-location is set to left. for certain pages (for example, about), i don't need a toc and so i turn it off in the page specific yaml. in doing this, i noticed that the page content became noticeably off-centered to the right:

i realized that this is because setting the page specific toc to false removes the quarto-margin-sidebar (where a toc on the right would normally appear) but not the quarto-sidebar that is added when toc-location: left (see image below). this would explain why removing the page specific toc on a website with toc-location: right leaves the resulting content centered (expected behavior) but a page with toc-location: left does not (unexpected behavior).

in full honesty, i actually expected that when toc-location: left the quarto-margin-sidebar would simply be moved to the left side of the page rather than having a second sidebar added instead. the current system causes content to be centered in a different way on pages with left hand vs right hand tocs even on the pages where the toc is present, which seems a bit surprising.

is this behavior expected?

Steps to reproduce

files to reproduce the above screenshot example.

index.qmd:

---
title: "Example"
toc: false
---

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_quarto.yml:

project:
  type: website

website:
  title: "sidebar_example"
  navbar:
    left:
      - href: index.qmd
        text: Home

format:
  html:
    theme: cosmo
    toc: true
    toc-location: left

Expected behavior

by default i would expect that setting toc-location: left moves quarto-margin-sidebar to the left side of the page rather than adding a second sidebar. even if adding a second sidebar is deliberate, i would expect that toc: false on a specific page removes both sidebars to produce an output equivalent to having toc: false on a page of website where toc-location: right.

Actual behavior

moving toc-location to the left (for overall website) adds a second sidebar on the left side of the page rather than moving the existing sidebar to the left. when toc: false for a specific page on a website with left-hand side tocs only the right hand sidebar is removed, resulting in off-center page content.

Your environment

• ide: vim 8.1 (rendering done in terminal)
• os: linux ubuntu 20.04
• quarto: 1.6.39

Quarto check output

Use the provided index.qmd and _quarto.yml reproduction with toc-location: left and a page-level toc: false. Render the site with Quarto and inspect the generated layout to determine why the left sidebar remains; done means disabling the page table of contents removes both sidebars and keeps the content centered.