The Flight package for code written against React `jsx` (`npm:react@19`), installed beside it: at the very version of that React, as Flight's halves are built for one React (each `planApp` keeps them together, through `tcm upgrade react` too). Writes the module the server renders with (`flightServerFile`). Its alias.
Server code's copy of an installed package (`entry`, its directory under the cache's `node_modules`: pnpm's `.pnpm/<entry>`, or npm's `<name>`, `@scope/<name>`), at that path under the cache's `server_modules`: its files hard-linked (nothing copied), its links to the packages it uses as they are, and (pnpm's, beside it in `.pnpm`) those packages copied too; npm's are found by name in `node_modules`, so `useFlight` makes their copies as they're asked for. Node keeps CommonJS modules by their paths, and remembers what a directory's `require("react")` found: a copy at its own paths gets its own, so server code's React (the react-server condition's) and server rendering's (`tcm dev` loads it with Node) never stand in for each other. Made once.
Render server component `fn` with `props` as Flight does (`useFlight` loads both): its tree, streamed as it's ready (`write`, text). An error inside it goes to `onError`, whose answer is the error's `digest`, what the browser is told of it in production. Done when all of it is written, or `signal` aborts.
Load the codebase's server code (the cache's modules, and the packages they import) as React's server components environment does: with the `react-server` condition, so it gets React's server build (`cache`, no hooks) and Flight's server. A module of browser code a server component renders (a component, a context it provides, a `lazy` one: `sent.client`) loads as Flight client references, by hash, instead of its code: it runs in the browser. A server function server components give the browser (`sent.server`) is registered as a server reference. Packages load from server code's own copies of them (`mirrorPackage`), so server rendering (the page's first paint), which has its own React, never shares one with it. For this process, from now on. `members` sees definitions not saved yet (a scratch file's tests).
A module of the server's (as it loads, `source`) with its imports of the packages' browser components it renders (`keys`, by `packageRefKey`) made Flight client references to them instead (`createClientReference` from `server`, the module `flightServerFile` writes): their packages aren't loaded on the server for them, and the browser, which has them, renders them. Declared first, so the module's own top-level code finds them.