Fix malformed SDK changelog redirects and close docs gaps found in 30-day analytics

[fern-api]

Data-driven docs fixes from 30 days of analytics, 404 logs, Ask AI unresolved conversations, and reader feedback.

docs.yml

• Add wildcard redirect /learn/api-definitions/protobuf/:slug* -> /learn/api-definitions/grpc/:slug*. The bare path logged 404s on live traffic; the Protobuf content lives under /learn/api-definitions/grpc/.
• Fix seven malformed SDK changelog redirects (TypeScript, Python, C#, Go, Java, Ruby, PHP) that used :slug* in the destination. A bare :slug* cannot hold a value containing /, so these resolved to the literal text :slug* in the URL — the exact failure mode documented on our own redirects page. Changed to :slug(.*) in both source and destination. Only the Python one appeared in the 404 log; the other six are the same latent bug on quieter paths.

seo/redirects.mdx

Add a "Moving to a new custom domain" section and rework the subtitle. A reader asked Ask AI how to forward an old custom domain to a new one and got nothing across three turns — even after saying "This docs site is specifically about redirects." The page never used the words "domain" or "forward traffic", so retrieval missed it entirely. The new section states that redirects are path-based only, and points domain-level forwarding at DNS / reverse proxy or Fern domain aliases.

navigation/tabs.mdx

Document that the theme.tabs object form requires Fern CLI 4.44.0+, and that the string shorthand works on all versions. Two readers hit theme.tabs publish failures within two days.

sdks/generators/python/configuration.mdx

Add a License section covering the pyproject_toml injection workaround. fern-python-sdk has no dedicated license key, unlike the Java generator's metadata.license; two Ask AI conversations on this went unresolved.

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Reviewer notes

Two things to check before this leaves draft:

1. The protobuf redirect may be redundant. The edit reports an exact-path /learn/api-definitions/protobuf redirect already existed in docs.yml, yet that path still logged 404s in the last 30 days. Either it was added after those hits, or it is not firing. Worth confirming which before treating that 404 as fixed.
2. The seven-redirect change alters production routing for every SDK changelog path and deserves a careful look.

Not addressed here (product bugs, not docs)

• Server-side rejection of valid theme.tabs object config at the ledger publish step. One affected user was on CLI 5.93.0 with fern check passing 0 errors, and had no locales block despite the error naming locales.0. The docs change here only records the version floor; it does not fix this.
• Ask AI generating links that omit the /learn prefix (and in one case corrupting the slug: preview-thpublish). Both substantive unhelpful votes in the last 30 days are this.
• Ask AI's guardrail refusing legitimate on-topic questions, e.g. "How do I create an organization?" Resolution rate is 73.8% (255/972 unresolved) and this looks like a meaningful share of it.

[github-actions]

🚫 [vale] _{reported by reviewdog 🐶}
[Microsoft.Contractions] Use 'can't' instead of 'cannot'.

[github-actions]

🌿 Preview your docs: https://fern-preview-2026-08-12-fern-ai-1fb7a4-06e524e7.docs.buildwithfern.com/learn

Here are the markdown pages you've updated:

• learn/docs/configuration/tabs
• learn/docs/seo/redirects
• learn/sdks/generators/python/configuration