Add WorkerdDebugPort interface for dynamic RPC entrypoint access

[danlapid]

Introduces a new privileged debug port interface that enables dynamic access to worker entrypoints at runtime.

Currently, service bindings between workerd processes must be configured at startup in the config file. Changing binding targets requires a full process restart. This is problematic for local development tools like Miniflare, which need to dynamically re-target RPC connections at runtime.

Today, Miniflare works around this by running a Node.js TCP server that sits between workerd processes and manually re-routes RPC traffic. This adds significant complexity and overhead.

This commit implements the WorkerdDebugPort interface which exposes all service entrypoints in a process through a privileged RPC interface. External tools can now:

• Get direct access to any entrypoint with custom props at runtime
• Start events and invoke methods via JS RPC without HTTP overhead
• Dynamically switch between entrypoints without process restarts

This enables Miniflare to eliminate its TCP proxy layer and handle dynamic RPC routing natively through workerd.

interface WorkerdDebugPort {
  getEntrypoint(service, entrypoint, props) -> (worker)
  getActor(service, entrypoint, actorId) -> (actor);
}

🤖 Generated with Claude Code

[codspeed-hq]

CodSpeed Performance Report

Merging #5568 will not alter performance

_{Comparing dlapid/debug_port (452a4c4) with main (f80cae3)}

Summary

✅ 57 untouched
⏩ 30 skipped¹

Footnotes

1. 30 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

[github-actions]

The generated output of @cloudflare/workers-types matches the snapshot in types/generated-snapshot 🎉

[kentonv]

It appears the intent here is to make WorkerdBootstrapImpl public, but this line actually makes the whole rest of the class public, including things that aren't needed.

It seems to me that WrokerdBootstrapImpl should actually be moved out of HttpListener. Previously it was an implementation detail used only by HttpListener, but now some other code unrelated to HttpListener wants to reuse the same implementation. So it needs to live elsewhere. And EventDispatcherImpl should probably become a private nested class inside WorkerdBootstrapImpl...

[kentonv]

This for loop and the confusingly-named acceptLoop() method (confusing because it doesn't encapsulate the loop) could be replaced with just using capnp::TwoPartyServer::listen(), which implements the accept loop for you.

[kentonv]

Use params.hasEntrypoint() rather than checking for a zero-length string. (Here and below.)

[kentonv]

Probably should check params.hasProps() and skip calling fromCapnp() on default props. (A default-initialized Frankenvalue is all you want.)

[kentonv]

This only supports Durable Objects. If the actor namespace is emphemeral (aka colo-local) then the ID is a plain string, not an ActorId.