fix: render SSR-enabled build entries once by teeing the RSC stream

[uhyo]

Summary

Fixes #147.

When ssr is enabled, build() in packages/static/src/rsc/entry.tsx rendered the identical element through two separate renderToReadableStream calls — one stream fed to renderHTML for SSR, the other written as the app RSC payload. As a result:

• every server component executed twice per entry (double data fetching / build work);
• every defer() call ran twice, registering duplicate registry entries whose payloads were both fully rendered (content hashing collapsed the duplicates to the same output file, hiding the waste but not avoiding it).

Change

Render the full tree once and tee() the resulting stream — one branch goes to renderHTML for SSR, the other becomes the app RSC payload. This halves build-time rendering per SSR entry and guarantees both consumers see byte-identical streams.

The tee()'d payload branch simply buffers while renderHTML drains the SSR branch; it is fully drained to a string shortly after in buildApp.ts, so there is no unbounded-buffering concern at build time. The non-SSR path is unchanged (its two streams render genuinely different trees). Dev-server rendering already used a single stream.

Testing

• pnpm build and pnpm typecheck pass
• pnpm test:run — 102 unit tests pass
• pnpm test:e2e — all 31 e2e tests pass, including the ssr-defer suite which exercises SSR builds with defer()

🤖 Generated with Claude Code

https://claude.ai/code/session_01ShuMmxpPtcxZrHMQZdbq2a

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