[Masad791]

Description

Fixes #14917.

Both problems from the issue came from the markdown pipeline that runs after the social meta tags are written:

• siteTitleMetaHandler always pushed the website title into og:site_name, so a page's open-graph.site-name never made it to the output.
• the handlers found their tags with doc.querySelector, i.e. the first match in <head>, so a tag from include-in-header or an extension got rewritten instead of Quarto's own.

writeMetaTag now returns the element it creates, the post processor keeps the tags it writes by name, and the pipeline handlers update those elements directly instead of searching the head. og:site_name now gets the same value the first pass writes: open-graph.site-name when the page sets it, the website title otherwise. Tags Quarto didn't write are left alone, which covers og:title, og:description, twitter:title and twitter:description as well.

Tests: a small website project under 2026/10/19/issue-14917 following the issue's repro. index.qmd checks the page's site name wins, and about.qmd adds decoy tags for all five names through include-in-header and checks they keep their values while Quarto's tags get the right ones. Both fail on main and pass with this change.

I also ran the existing social metadata tests (27 smoke-all documents plus smoke/site/render-website-image-data-uri.test.ts). All pass except 2024/10/28/issue-10311, which needs Jupyter; it fails the same way on main on my machine.

Checklist

I have (if applicable):

• referenced the GitHub issue this PR closes
• updated the appropriate changelog in the PR
• ensured the present test suite passes
• added new tests
• created a separate documentation PR in Quarto's website repo and linked it to this PR

AI-assisted PR

• AI tool used: Claude Code
• Codebase grounding: local clone
• Human review: I have reviewed, tested, and verified the AI-generated content before submitting.

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[cderv]

Thanks for the PR.

Keeping the elements Quarto writes is the right fix I think. The markdown pipeline pass is what resolves markdown and shortcodes in the site title, so it can't be dropped, and nothing in the output marks which tags Quarto wrote, so a narrower selector would not work.

I can reproduce the issue on main and the PR fixes it, also for a page site-name with markdown or a shortcode, and for one set in _metadata.yml.

I'll push a few small adjustments on your branch before merging, no need to change anything on your side.