Add capnweb-typecheck for TypeScript RPC validation codegen

[teamchong]

Summary

Adds build-time TypeScript RPC validation codegen to the single capnweb package. The capnweb bin reads RpcTarget classes from TypeScript and generates runtime validators that fire when RPC methods are called.
capnweb stays dependency-free at install time. Tooling is exposed as the capnweb typecheck gen CLI command, capnweb/vite, and the generated-code-only capnweb/internal/typecheck subpath.

What this PR adds

Typecheck tooling in capnweb:

• capnweb CLI (bin) for Wrangler-style builds: capnweb typecheck gen src/worker.ts --out .capnweb.
• capnweb/vite plugin for Vite builds.
• No typia, no ts-morph, no .npmrc, and no separate packages/capnweb-typecheck package.
• Codegen uses the local TypeScript compiler API plus local validator metadata/runtime.
• For each typed RpcTarget method, the generator emits runtime validators for every parameter and return value, plus glue that registers them on the class at startup. Generated artifacts are written to .capnweb/ (configurable).

Runtime integration:

• Zero runtime dependencies.
• New internal subpath capnweb/internal/typecheck consumed only by generated code, not by user code.
• Server-side validation: keyed by RpcTarget constructor; runs in deliverCall() before invoking the method and before returning a result.
• Client-side validation: bound to the original RpcStub, preserving RpcPromise pipelining, disposal, and StubBase semantics. Typed new RpcSession<T>(...) is supported via a session-shape wrapper that binds validators on session.getRemoteMain() without changing the caller-visible value.

VS Code Debug

1. In a JavaScript Debug Terminal:

./examples/worker-react/dev-debug.sh

# ./examples/worker-react/dev-debug.sh --typecheck # for checking how the typecheck work

2. In VS Code Command Palette, run Debug: Open Link and open:
   http://127.0.0.1:5173

Set breakpoints in examples/worker-react/web/src/main/App.tsx, then click Run demo.

Testing

• npm run build
• npm run test:types
• npm run test:bun
• npx vitest run --no-coverage tests/typecheck.test.ts tests/vite-plugin.test.ts
• npx vitest run --no-coverage --project node
• ./examples/worker-react/dev-debug.sh smoke reached http://127.0.0.1:5173
• ./examples/worker-react/dev-debug.sh --typecheck smoke reached http://127.0.0.1:5173

Changeset
.changeset/typescript-rpc-validators.md — minor bump for capnweb.

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🦋 Changeset detected

Latest commit: 23c1f7e

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

This PR includes changesets to release 1 package

Name	Type
capnweb	Minor

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commit: 23c1f7e