Function executeRouter

packages/start-server-core/src/createStartHandler.ts:544–614

(
        serverContext: TODO,
        matchedRoutes?: ReadonlyArray<AnyRoute>,
      )

      // Router execution function
      const executeRouter = async (
        serverContext: TODO,
        matchedRoutes?: ReadonlyArray<AnyRoute>,
      ): Promise<SsrResponse> => {
        const acceptHeader = request.headers.get('Accept') || '*/*'
        const acceptParts = acceptHeader.split(',')
        const supportedMimeTypes = ['*/*', 'text/html']

        const isSupported = supportedMimeTypes.some((mimeType) =>
          acceptParts.some((part) => part.trim().startsWith(mimeType)),
        )

        if (!isSupported) {
          return normalizeSsrResponse(
            Response.json(
              { error: 'Only HTML requests are supported here' },
              { status: 500 },
            ),
          )
        }

        const manifest = await resolveManifestForRequest({
          request,
          requestInlineCss: requestOpts?.inlineCss,
          getBaseManifest: () => getBaseManifest(matchedRoutes),
        })

        const earlyHints = createEarlyHintsForRequest({
          onEarlyHints: requestOpts?.onEarlyHints,
          responseLinkHeader: requestOpts?.responseLinkHeader,
        })

        earlyHints?.collectStatic({ manifest, matchedRoutes })

        const routerInstance = await getRouter()

        attachRouterServerSsrUtils({
          router: routerInstance,
          manifest,
          getRequestAssets: () =>
            getStartContext({ throwIfNotFound: false })?.requestAssets,
        })

        // `additionalContext` is request-scoped and only read from router.options
        // during load; avoid a full router.update() and redundant location parse.
        routerInstance.options.additionalContext = { serverContext }
        await routerInstance.load()

        if (routerInstance.state.redirect) {
          return normalizeSsrResponse(routerInstance.state.redirect)
        }

        earlyHints?.collectDynamic(routerInstance.stores.matches.get())

        // Pass request-scoped assets to dehydrate for manifest injection
        const ctx = getStartContext({ throwIfNotFound: false })
        await routerInstance.serverSsr!.dehydrate({
          requestAssets: ctx?.requestAssets,