SolidJS · roadmap.sh · Express · FastAPI
SolidStart: route file naming convention 
In the early days after SolidStart's release, the routing convention described the folder-named route file convention incorrectly. People following it ended up with routes that didn't render, and it kept coming up in the Solid and JavaScript Discords. I corrected it: the file has to be wrapped in parentheses, e.g. (socials).tsx. Reviewed and approved by SolidJS core maintainer Atila Fassina (a friend of mine).
roadmap.sh: "Busy Frontend" entry
roadmap.sh is one of the top 10 most-starred repositories on all of GitHub (369k★) and a go-to learning reference for engineers. I rewrote the "Busy Frontend" entry. It covers a fairly advanced concept, so the wrong explanation went unnoticed for a long time and confused a lot of readers.
Express: request-lifecycle observability 
I opened the first PR implementing diagnostics_channel events for the Express request lifecycle (#6353). With these events, monitoring tools like OpenTelemetry, Sentry and Datadog can trace requests without monkey-patching Express. While reviewing my PR, an engineer from Sentry proposed moving the instrumentation into Express's router and using TracingChannels for context propagation. He opened pillarjs/router#196 the next day (it credits my PR in its description as the same feature), and the maintainers marked mine as superseded by it. It's now merged and slated for the next release, shipping to Express 5.
FastAPI: AliasChoices for request params 
My team hit this in production: AliasChoices validation aliases were silently ignored for Query / Header / Cookie / Form params. I fixed it with regression tests and the full suite passing. Sebastián Ramírez (FastAPI's creator) closed it "for now" (not because the fix was invalid: he wants to land a bigger refactor of that code first, which he expects to cover the same issue) (see thread).
Loonaris: a production-grade, multi-tenant PostgreSQL DBaaS on AWS / Kubernetes. I built a custom PostgreSQL wire-protocol proxy for tenant-aware routing, plus automated provisioning, replication and failover. Each tenant gets an isolated cluster in under 30 seconds.