fix: collapse React to a single optimized chunk to prevent duplicate React on cold start

[uhyo]

Summary

Fixes #128 — on a cold-started dev server (no .vite cache), React was loaded twice on the very first request, producing an Invalid hook call before Vite auto-reloaded. Also fixes the related fsRoutes-without-ssr:true dev failure (#124), where the eval'd dev-JSX could not resolve react/jsx-runtime (does not provide an export named 't').

This is an alternative to #129 that makes the failure mode structurally impossible rather than merely avoided. See the root-cause investigation on #128 for the full analysis.

Root cause (one bug, two symptoms)

A dependency that @vitejs/plugin-rsc reaches through a request-time client-package-proxy virtual module (e.g. @funstack/router) is invisible to the dependency optimizer's initial scan, so it is only discovered on the first render. That late discovery triggers a re-optimization pass which, mid-flight, corrupts CJS-interop module references:

• React loads twice in first load from cold started dev server #128: we registered React as two optimized chunks of the same source file — bare react (scanned) and @funstack/static > react. The optimizer dedups them within a pass (one canonical, one re-export), but the re-optimization flips which chunk is canonical. Modules loaded before the flip bind to one real React instance; @funstack/router (optimized after) binds to the other → two live React instances → Invalid hook call.
• File-system routing requires ssr: true for the dev server (lift this limitation) #124: the eval'd dev-JSX references a pre-re-optimization version of react/jsx-runtime, which no longer matches after the pass → does not provide an export named 't'.

Both vanish on reload because everything then agrees on the post-re-optimization state — hence the cold-start-only, first-render-only nature.

Fix

Two coordinated changes:

1. Pre-bundle the project's client packages (direct deps that declare react as a peerDependency — the same heuristic plugin-rsc uses) in the browser environment, so they are discovered in the optimizer's initial pass and no re-optimization happens on the first render. (findClientPackages)
2. Use bare react/react-dom instead of the nested @funstack/static > react form. The bare specifiers merge with the copy the scanner already discovers, so React is bundled into a single optimized chunk — making the duplicate-React flip impossible even if a re-optimization ever slips through.

Why both: bare React alone can't ship — it regresses #124 (that's why the nested form was added in #126). Pre-discovery fixes #124's real cause; the single chunk makes #128 impossible by construction. This is strictly stronger than #129, which keeps the redundant second React chunk and only avoids the flip.

Notes:

• Scoped to direct dependencies (bare specifiers a server component can import and Vite can resolve from the project root). @funstack/static (excluded from optimizeDeps) and react-dom (handled separately) are skipped. The react-in-peerDependencies key excludes build plugins like @vitejs/plugin-react (peer-depends on vite), so no false positives.
• The previous hardcoded reliance on the nested React form is removed; client packages are auto-detected in all entry modes.

Verification

• Reproduced the cold-start Invalid hook call reliably before; after, multiple cold starts are clean (single React chunk, no re-optimization, no auto-reload) with zero user config — verified with a Playwright + .vite/deps/_metadata.json harness that asserts both File-system routing requires ssr: true for the dev server (lift this limitation) #124 and React loads twice in first load from cold started dev server #128.
• New unit tests: clientPackages.test.ts (fixture-based detection) + index.test.ts (single-chunk + client-env-scoped pre-discovery). Full unit suite (60), typecheck, lint, format:check pass.
• Dev e2e (24/24) and build e2e (27/27) pass across single-entry, multi-entry, ssr-defer, and fs-routing modes.

Fixes #128

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