refactor(chat)!: namespace exports for React Server Component support - #53

Makes the primitives usable from React Server Components, by switching from Object.assign compounds to Base UI-style namespace exports.

The problem

Every compound sub-component resolved to undefined in a server component:

// Server component → "Element type is invalid… but got: undefined"
<Composer><Composer.Container /></Composer>

A server component importing a "use client" module receives a proxy of that module's named exports. It cannot read properties off an exported value — and Object.assign(ComposerRoot, { Container }) is exactly that. Bare <AskUser /> worked; <AskUser.Header /> did not.

The shape

Base UI's structure, verified against their published output: the barrel and the parts layer carry no directive, and it lives one level down on the component module.

src/message/message.tsx        "use client" — MessageRoot, MessageText, …
src/message/index.parts.ts     no directive — export { MessageRoot as Root, … } from "./message"
src/message/index.ts           no directive — export * as Message from "./index.parts"
                                            + flat type / hook re-exports

Unlike Base UI we don't need a file per part — the boundary only has to sit below the barrel — so each component stays in one file and the single-file convention survives.

I proved the mechanism in an isolated spike before touching anything, with both shapes in one Next app:

Breaking change

<Composer> → <Composer.Root>, and likewise for Message, Thread, Steps, Reasoning, Chip, Attachments, AskUser. Sub-component names, hooks and type names are unchanged, so migration is mechanical. Changeset included.

The build had to change too

A bundle carries one top-level directive, so bundling collapses the per-part boundaries this depends on. The package now ships unbundled — one module per source file, emitted by tsc instead of bunup.

That deleted two workarounds from #51 rather than carrying them forward:

• dts: { inferTypes: true } is gone. tsc infers declarations natively; there is no isolated-declarations pass to erase Object.assign compounds to unknown.
• NODE_ENV=production is gone. tsc always emits the production react/jsx-runtime, so the dev-runtime bug can't recur from an unset env var.

One wrinkle worth recording. I first added .js extensions to the src imports, which is the conventional ESM-first approach — and Turbopack refused to resolve ./actions.js against actions.tsx. It has no extensionAlias equivalent, so that broke the app's transpilePackages dev loop, which deliberately compiles package source with no build step. Source therefore stays extensionless and scripts/add-dist-extensions.mjs adds extensions to the emitted output instead (231 specifiers). Dev loop unchanged, dist valid ESM, publint clean.

Tarball grew: 74.5 kB packed across 25 bundled files → ~102 kB across 115 unbundled files. Unpacked is slightly smaller since internal/ helpers are no longer duplicated per entry, but per-file gzip is less efficient. That's the price of correct client boundaries.

Docs

AGENTS.md now describes both layers explicitly, because they legitimately differ: the app layer (components/ai/, components/ui/) keeps Object.assign and stays single-file copy-pasteable, while the package uses namespace exports. Rule 13 forbade barrel files, which the new pattern requires, so it carries an explicit exception. Both invariants that make this work — the barrels staying directive-free, and the build not bundling — are written down where someone would otherwise break them.

Also updated: the package README's RSC section (its constraint is gone, replaced by a server-component transcript example), CHAT_ARCHITECTURE.md, and the content/docs/primitives/* pages — including their source: frontmatter, which pointed at files that moved. COMPOSER.md, THREAD.md, MESSAGE.md and DESIGN_SYSTEM.md document the app layer, so their <Message> examples are still correct and untouched.

Verified

Against the packed tarball, installed into a Next 16 app with no transpilePackages:

• A server component rendering Thread.Root / Message.Root / Message.Text / Chip.Root / Chip.Icon / Chip.Label / Reasoning.* / Steps.* / AskUser.* prerenders, with all 16 expected data-* part attributes in the HTML
• A client component using the same namespaces plus useComposer / useThread / useReasoning and event handlers builds and prerenders
• 179 tests, both typechecks, biome, publint, and the app build (dev path via transpilePackages) all green