Decouple from Express: support other HTTP frameworks

[felixweinberger]

Summary

Decouple the SDK from Express to allow for a lighter SDK and easier compatibility with other HTTP frameworks (e.g., Hono, Fastify, and others).

This was identified as a gap in the v2 wishlist (issue #809) that is not yet tracked as a separate issue.

Motivation

• Lighter SDK: Users who don't need HTTP server functionality shouldn't need Express as a dependency
• Framework flexibility: Many TypeScript developers prefer alternatives to Express (Hono, Fastify, h3, etc.)
• Serverless compatibility: Lighter frameworks work better in serverless/edge environments
• Bundle size: Reducing dependencies improves build times and bundle size

Requirements

1. Abstract HTTP framework-specific code behind interfaces
2. Provide adapters for popular frameworks (Express, Hono, Fastify)
3. Allow users to bring their own HTTP framework
4. Maintain backwards compatibility with existing Express-based code

Related Issues

• Fix packaging with tsdown, export from root, shims for different runtimes #1255 (Fix packaging with tsdown)
• Non-Node environment support (Bun, Deno, React Native) #1269 (Non-Node environment support)
• SDK V2 #809 (SDK V2 wishlist)

Labels

• v2
• breaking change
• enhancement