feat: add record and replay proxy for automatic fixture generation

[mvanhorn]

Summary

Add emulate record command that proxies requests to real APIs, records the traffic, and generates an emulate.config.yaml with extracted seed entities when you press Ctrl+C. Point your app at the local proxy, use it normally, and get a config file with realistic data.

Why this matters

Setting up seed data for emulate requires manually writing YAML configs. For APIs with nested relationships (repos with issues, customers with payment methods), this is tedious and the resulting fixtures may not match real API response shapes.

Mockoon and WireMock both have recording proxy modes. This brings the same capability to emulate, with the added benefit of generating emulate-native seed configs rather than generic mock definitions.

Changes

• packages/emulate/src/commands/record.ts: New command implementing the proxy server, traffic recording, and entity extraction. Includes extractors for GitHub (users, repos from response bodies) and Stripe (customers, products).
• packages/emulate/src/index.ts: Registered the record command with --service, --upstream, --port, and --output flags
• README.md and skills/emulate/SKILL.md: documented the new command with examples and flag reference

Demo

Shows the recording proxy starting, forwarding a request to GitHub's API, then generating a seed config on shutdown with the extracted user and repo entities.

How it works

1. Starts a Hono server on the configured port
2. Every request is forwarded to the --upstream URL with original headers
3. Response is returned to the caller and recorded in memory
4. On Ctrl+C, recorded responses are analyzed by service-specific extractors
5. Extracted entities are written as an emulate.config.yaml

Entity extraction is service-specific. Currently GitHub and Stripe have extractors. Other services proxy correctly but don't extract entities yet.

Testing

Existing tests pass. The proxy and entity extractors are pure functions that can be unit tested independently.

This contribution was developed with AI assistance (Claude Code).

[vercel]

@mvanhorn is attempting to deploy a commit to the Vercel Labs Team on Vercel.

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[mvanhorn]

Fixed both findings in 5b655d1:

• Wrapped the upstream fetch() in try/catch to return a 502 with the error message instead of an opaque 500
• Normalized --upstream URL by stripping trailing slashes to prevent double-slash in request URLs