Link previews to pxxc.org render as bare text — no og:image

Found 2026-08-27 while checking whether the site is legible to non-browser fetchers (agent crawlers, link unfurlers, search summarisers). The fetchability verdict was good — see [[feature-web-machine-readable-project-metadata]] for what was still missing — but the social-card surface is empty.

Fix lands in the private ~/pxx-website repo, not in this checkout.

RESOLVED 2026-08-27 — DEPLOYED AND VERIFIED LIVE

Fixed by e78595d on the website repo, deployed to via, gunicorn restarted.

Served from pxxc.org, fetched from the public internet by frank2-af:

<meta property="og:image" content="https://pxxc.org/static/img/og-card.png">
<meta property="og:image:width" content="1200">
<meta property="og:image:height" content="630">
<meta property="og:image:alt" content="pxx — a Pascal and C compiler">
<meta name="twitter:card" content="summary_large_image">
<meta name="twitter:image" content="https://pxxc.org/static/img/og-card.png">

/static/img/og-card.png -> HTTP 200, 29667 bytes, image/png, decodes 1200x630 RGB

Verified on two independent instruments, deliberately — the failure mode this lane hit all day was a correct reading of the wrong one:

The detail most likely to have shipped silently broken was the absolute URL: canonical_url ~ url_for(...) had to produce https://pxxc.org/..., because a relative og:image unfurls as nothing. It resolved correctly, and the public fetch is what proves it rather than the template.

Do not overwrite og-card.png in place. nginx serves static/ with expires 1h and no fingerprint, so a replaced asset is stale at the edge for up to four hours. Ship a new filename and update the template.

Superseded status notes (kept for the sequence)

What visitors get right now: the pre-fix tags. twitter:card=summary, no og:image. A link to pxxc.org still unfurls as a bare text row. That is the one line to carry forward — a future session reading "p45 committed" will reasonably assume the site serves a card, and it does not.

State from the origin side, reported by ianweb on via (the only session that can observe it):

Three distinct states, and the middle one is where this sits: committed → reviewed-and-fetched-but-not-merged → served. Only the third changes what anyone sees.

Why it is not deployed, and why that is correct. deploy/DEPLOY-STATUS.md: "Deploys stay manual on purpose: auto-deploy would let a compromised GitHub account run code on the host." An agent pushing a commit and then asking the agent on the host to pull it is structurally what that gate exists to stop — benign here, since ianweb read every line and recommends it, but "I checked and it's fine" is precisely what the gate is designed not to depend on. It is the same reasoning that kept push keys off via, pointed the other way down the same pipe.

Remaining steps, neither of them a coding task:

1. A human go/no-go on the deploy.
2. git pull on via, then sudo systemctl restart pxxweb — Jinja caches compiled templates in the worker, so a pull alone changes nothing served.
3. The rendered <meta> lines captured from the origin and pasted into this ticket. An outside audit cannot distinguish "not deployed" from "deployed and edge-cached", so this verification has to come from via.

This ticket resolves on step 3, not on the commit. Everything about the p45 is done except the one step that makes it real.

What landed (for the record)

Fixed in the website repo as e78595d ("Link previews: an Open Graph card, and the large-image Twitter card"), pushed to origin/main.

• pxxweb/static/img/og-card.png — 1200x630, new directory
• pxxweb/templates/base.html — og:image (+ width/height/alt), twitter:image, and twitter:card raised to summary_large_image
• scripts/make-og-card.py — the card is generated, not hand-drawn, so a copy change is a one-line edit and a re-run

Not closed yet, deliberately. Two steps remain and neither is mine:

1. A gunicorn restart on via. Jinja caches compiled templates in the worker, so git pull alone does not change what visitors are served. Until that happens the tags are in git and not on the wire.
2. Confirmation of the served result, from the origin. An outside audit cannot distinguish "not deployed" from "deployed and edge-cached", so the check has to come from via. ianweb has it.

Safe to land ahead of [[bug-web-production-tree-is-uncommitted-and-is-the-only-copy]] because the edit was made in a clean clone and pushed, not made on via. ianweb verified the part only it could: git diff --name-only on via does not list base.html, so the pull fast-forwards cleanly and leaves the six uncommitted files alone. That is also why this ticket and its three siblings no longer declare the p70 as a blocker — see that ticket for why the premise narrowed.

Do not overwrite og-card.png in place. nginx serves static/ with expires 1h and no fingerprint in the URL, so a new file needs no purge but a replaced one is served stale from the edge for up to four hours. Ship a new filename and update the template instead.

The measurement

curl -sSL https://pxxc.org on 2026-08-27, grepping the rendered <head>:

So the metadata is otherwise complete and correct — this is a single missing asset, not a neglected head section.

Why it matters more than it looks

Unfurlers fall back to a text-only row when og:image is absent. On the channels where a compiler project actually gets discovered — HN, Reddit, lobste.rs, Mastodon, a Slack or Discord where someone pastes the link — that row sits directly beside entries that carry a picture, and it loses the comparison every time. twitter:card: summary compounds it: even once an image exists, summary renders a small thumbnail, where summary_large_image gives the wide card.

This is the cheapest real gain available on the site right now. It does not improve the page for anyone already reading it; it improves the odds that someone clicks through at all.

What to do

1. Author an OG card image, 1200x630, and serve it from /static/. It must read at thumbnail size — the project name plus one line, not the landing page's full feature list shrunk down.
2. Add <meta property="og:image" content="https://pxxc.org/static/og.png"> (absolute URL — several unfurlers do not resolve relative ones), plus og:image:width / og:image:height / og:image:alt.
3. Change twitter:card to summary_large_image.
4. Consider a PNG favicon alongside the SVG; a few older unfurlers and browsers ignore image/svg+xml.

Claims discipline applies to the card

The card image is public-facing copy in the sense CLAUDE.md means it, and it is the most compressed surface the project has — a headline with no room for qualifiers. So it must not carry any form of the byte-identical claim. "Self-hosting Pascal and C compiler" is safe; anything about matching gcc is not, at any length that fits on a card. The landing page currently gets this right and a summariser confirmed it (see [[feature-web-machine-readable-project-metadata]]); the card is where that discipline is most likely to be lost first.

Gate

Fetch the page, confirm the tags are present, and validate the rendered card against at least two unfurlers before closing.

Log

• 2026-08-27 — resolved, commit 86911308f.