feat: add ssr: "data-only" (1.x)

[lxsmnsyc]

For #2287 on the 1.x line. The same feature for 2.x is in #2352.

What this adds

export default defineConfig({ ssr: "data-only" });

The app renders on the client with render(), as with ssr: false, so there's no hydration and no app HTML from the server. The server still runs the route preloads for the requested page and streams their query results with the HTML shell. On the first render, the client's queries take those results instead of fetching them again.

How it works

The design is the same as #2352.

Server. The router's data-only pass collects the page's query promises. Single-flight mutations already use this pass in runtime/server-handler.ts. The SPA shell then renders with renderToStream, and each promise goes to sharedConfig.context.serialize under a <Hydration> boundary, which is Solid's own SSR serializer. <HydrationScript eventNames={[]}> defines _$HY.r.

Responses from a query. query skips its own Response handling in data-only mode, so it's applied here:

• Headers are copied to the page response, except the body headers.
• A redirect that's known before the shell flushes becomes a real redirect, and a thrown redirect isn't reported as an error.
• A json() response sends its body.

Client. mount() points sharedConfig.has/sharedConfig.load at _$HY.r for the first render(). Router 0.15's query reads serialized data through them, the same as router 1.0.

Differences from 2.x

• ssr: false prerenders / into a static shell. Data-only mode doesn't, because each request needs its own data.
• The client Solid plugin received ssr: start.ssr, and the "data-only" string would have turned on hydratable output. It now gets start.ssr === true.
• The SPA server entry now exports the deprecated getServerFunctionMeta, as the SSR entry does. decorateHandler and decorateMiddleware don't exist on 1.x.

Limits

These are the same as #2352:

• Data needs a streamed render: nothing is sent with mode: "sync".
• The root renders on the server during the data pass. If it throws there, the client fetches its data as before.
• Query data uses Solid's serializer plugins, the same as SSR query data.

Verification

Production build of the basic fixture with a route whose preload calls four queries (data, json() with set-cookie, a throw, and a redirect on another route):

Check	Result
Shell	streams _$HY.r[...] for each query; Content-Type: text/html; set-cookie from the json() query
Client	renders with the streamed data, Date and Map intact, error shown by the ErrorBoundary, 0 server function calls
Redirect route	302 with location: /co-b
Client navigation to the page	fetches as usual (3 calls)
ssr: false	still prerenders .output/public/index.html, no _$HY

• packages/start: 106 unit tests (11 new), typecheck and build pass.
• apps/tests: the unit test passes. Cypress: 18 of 19 pass.
• The one Cypress failure is server-function.cy.ts › "should reject the promise when the response is a 5xx without an X-Error header". It fails the same way on clean 1.x.

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Latest commit: ef2391d

The changes in this PR will be included in the next version bump.

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Name	Type
@solidjs/start	Minor

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