Fastify v5.8.3

⚠️ Security Release

This fixes CVE CVE-2026-3635 https://github.com/fastify/fastify/security/advisories/GHSA-444r-cwp2-x5xf.

What's Changed

• docs(readme): add @Tony133 to plugin team by @Tony133 in https://github.com/fastify/fastify/pull/6565
• Updated Plugins-Guide.md; Changed "fastify" to "instance" during plugin registration to showcase that it's added as a child by @kyrylchenko in https://github.com/fastify/fastify/pull/6566
• test: use fastify.test in test case by @climba03003 in https://github.com/fastify/fastify/pull/6568
• docs: use fastify.example in documentation by @climba03003 in https://github.com/fastify/fastify/pull/6567
• docs: add common performance degradation guidance by @maxpetrusenko in https://github.com/fastify/fastify/pull/6520
• docs(server): fix camelCase anchor links in TOC by @Deepvamja in https://github.com/fastify/fastify/pull/6530
• ci(link-checker): fix root-relative links resolution by @barba-rossa in https://github.com/fastify/fastify/pull/6535
• docs: update syntax markdown, absolute paths and links by @Tony133 in https://github.com/fastify/fastify/pull/6569
• docs: clarify content-type parser/schema mismatch is outside threat model by @mcollina in https://github.com/fastify/fastify/pull/6537
• docs: fix incorrect code examples in Reply and Request reference by @mahmoodhamdi in https://github.com/fastify/fastify/pull/6582
• docs: replace redirected npm.im http-errors link by @mcollina in https://github.com/fastify/fastify/pull/6588
• types: Allow port to be null in request type definition by @TristanBarlow in https://github.com/fastify/fastify/pull/6589
• docs: update links by @Tony133 in https://github.com/fastify/fastify/pull/6593
• ci(lock-threads): use shared lock-threads workflow by @Fdawgs in https://github.com/fastify/fastify/pull/6592

New Contributors

• @kyrylchenko made their first contribution in https://github.com/fastify/fastify/pull/6566
• @maxpetrusenko made their first contribution in https://github.com/fastify/fastify/pull/6520
• @Deepvamja made their first contribution in https://github.com/fastify/fastify/pull/6530
• @barba-rossa made their first contribution in https://github.com/fastify/fastify/pull/6535
• @mahmoodhamdi made their first contribution in https://github.com/fastify/fastify/pull/6582
• @TristanBarlow made their first contribution in https://github.com/fastify/fastify/pull/6589

Full Changelog: https://github.com/fastify/fastify/compare/v5.8.2...v5.8.3