fix(docs): name the SDK on the aged-out reference notice

[posthog]

Changes

Readers who ask for an SDK reference version that aged out of the build get a notice page. That page was written to name the SDK and version they asked for, and to link to the current reference for that SDK. It never did either: everybody got the generic copy, whose only link is "Browse all SDK docs".

Problem

• A reader who asks for an old version is told nothing about their SDK, and is sent to the full library index to search for the page by hand. This happens every day, to a steady stream of readers, and to AI assistants that fetch these URLs.
• version-unavailable.tsx read the SDK and version from window.location.pathname after mount.
• The vercel.json rewrite is transparent, but Gatsby is not: when the served page's window.pagePath differs from the browser path, Gatsby's runtime replaces the address bar with the page path and keeps only the query string (production-app.js). Behind this rewrite that is always true, so the parse always failed.

Fix

• Read the requested URL from the navigation timing entry (performance.getEntriesByType('navigation')[0].name). It records the URL the document was fetched with, and the history replacement does not change it.
• The ?ref= override and the parser are unchanged.

Two approaches that do not work

Approach	Why not
Pass the slug through the rewrite, ?ref=:slug	A rewrite destination's query string is server-side only. It never reaches the browser, so the page cannot read it.
Redirect instead of rewrite	Redirects run before the filesystem check, so the rule would also capture the versions that do have pages. Rewrites run after it, which is why only aged-out URLs reach this page.

Version picker (SdkReference.tsx): no change. It lists every sourced version on purpose, and Gatsby falls back to a full page load when a page fails to load, so a picker entry with no page reaches the rewrite and now gets the named notice.

Screenshots

The "after" column is production, opened with the ?ref= override that already renders this branch. The environment cannot build the site, so the branch itself is not pictured; the override feeds the same JSX the fix feeds.

	Before	After
Light, narrow
Light, wide
Dark, narrow
Dark, wide

How the root cause and the fix were verified

Headless Chromium, against production, on /docs/references/posthog-react-native-4.61.0:

• location.pathname reads /docs/references/version-unavailable, which confirms the parse can never succeed. The page renders the generic copy.
• performance.getEntriesByType('navigation')[0].name still reads https://posthog.com/docs/references/posthog-react-native-4.61.0.
• The new resolver, run in that page, returns { sdk: 'posthog-react-native', version: '4.61.0' }. It also resolves a types subpath (/docs/references/posthog-js-1.203.1/types/Survey) and the ?ref= override.

pnpm format (Prettier 2, repo config) and node --test src/components/SdkReferences/utils.test.ts both pass.

Not tested: the dev server and the production build. This environment has no node_modules and cannot install them, so there is no local console check. The Vercel preview build covers both.

Checklist

• I've read the docs and/or content style guides.
• Words are spelled using American English
• Use relative URLs for internal links
• I've checked the pages added or changed in the Vercel preview build — this environment cannot build or open the site; please check the preview
• If I moved a page, I added a redirect in vercel.json — no page moved

---

Created with PostHog Desktop from this inbox report.

🤖 Generated with Claude Code

[posthog]

🦔 PostHog Review reviewed this pull request

Nothing worth raising this time, so here's a calming picture instead:

[github-actions]

Deploy preview

Status	Details	Updated (UTC)
🟢 Ready	View preview	Sep 15, 2026 05:39AM

[github-actions]

Bundle report

Total JS (gzip)

8.78 MiB (+0.1 KiB / +0.0%)

Eager graph (modules shipped in each entrypoint's initial chunks)

Entrypoint	Eager size	Budget	Modules
✅ app	18.51 MiB (no change)	report-only	2062

Largest modules in the app closure

Module	Size
./src/data/mcp-tools.json	1137.8 KiB
css ./node_modules/.pnpm/css-loader@5.2.7_webpack@5.101.3/node_modules/css-loader/dist/cjs.js??ruleSet[1].rules[8].oneOf[1].use[1]!./node_modules/.pnpm/postcss-loader@4.3.0_postcss@8.5.6_webpack@5.101.3/node_modules/postcss-loader/dist/cjs.js??ruleSet[1].rules[8].oneOf[1].use[2]!./src/styles/global.css	773.5 KiB
./src/components/Stickers/Stickers.tsx	696.4 KiB
./node_modules/.pnpm/@radix-ui+react-icons@1.3.2_react@18.3.1/node_modules/@radix-ui/react-icons/dist/react-icons.esm.js	481.4 KiB
./node_modules/.pnpm/@posthog+brand@0.8.0_react@18.3.1/node_modules/@posthog/brand/dist/generated/hoggies/svg/x-ray.mjs	480.8 KiB
./node_modules/.pnpm/rehype-raw@7.0.0/node_modules/rehype-raw/lib/index.js + 29 modules	395.1 KiB
./node_modules/.pnpm/@posthog+brand@0.8.0_react@18.3.1/node_modules/@posthog/brand/dist/generated/hoggies/svg/im-the-driver.mjs	385.7 KiB
./src/hooks/useCustomers.tsx + 55 modules	370.0 KiB
./node_modules/.pnpm/@posthog+icons@0.36.6_react-dom@18.3.1_react@18.3.1__react@18.3.1/node_modules/@posthog/icons/dist/posthog-icons.es.js	354.8 KiB
./node_modules/.pnpm/react-markdown@8.0.7_@types+react@16.14.66_react@18.3.1/node_modules/react-markdown/lib/react-markdown.js + 88 modules	351.4 KiB
./src/components/ProductComparisonTable/index.tsx + 126 modules	305.7 KiB
./node_modules/.pnpm/cloudinary-core@2.14.0_lodash@4.17.21/node_modules/cloudinary-core/cloudinary-core.js	281.9 KiB
./node_modules/.pnpm/@posthog+brand@0.8.0_react@18.3.1/node_modules/@posthog/brand/dist/generated/hoggies/svg/doll-house.mjs	281.7 KiB
./node_modules/.pnpm/@posthog+brand@0.8.0_react@18.3.1/node_modules/@posthog/brand/dist/generated/hoggies/svg/director.mjs	275.6 KiB
./src/components/SearchUI/index.tsx + 87 modules	273.7 KiB

---

Eager-graph budgets are report-only until a baseline is established. Sizes are gzip of public/**/*.js; eager size is webpack module source bytes for the modules actually shipped in the entrypoint's initial chunks (post-tree-shake).