node: allow one pinned actor to use isolate port scope

[petebacondarwin]

Summary

#7306 correctly made Node.js virtual port tables Durable Object instance-scoped. Vite and Vitest, however, evaluate user modules inside pinned synthetic runner actors and later invoke the exported handlers from their real I/O contexts. A Node server registered during module evaluation is therefore currently invisible to httpServerHandler() during dispatch.

This adds an unsafe Durable Object namespace option whose value names the one ephemeral-local actor allowed to use its worker isolate's Node port table. The namespace compares each actor's ID before carrying that scope choice into Worker::Actor, where cloudflare-internal:sockets selects the isolate table.

Configuration is rejected if preventEviction is absent, if the namespace is not ephemeral-local, or if another namespace in the same Worker already names an isolate-scope actor. All other durable and ephemeral-local actors retain their per-instance port tables.

Why this is in workerd

Redirecting handler invocation back through the synthetic runner actor can make a trivial GET pass, but changes the request/response transport boundary and breaks body and streaming semantics. The runner actor is an artificial module-evaluation context, so selecting the intended port-table host at the runtime boundary preserves normal handler dispatch.

Feedback requested

This is a draft to align the runtime and tooling teams before settling the API. In particular:

• Is an actor-ID-valued namespace escape hatch the right representation for an internal pinned actor?
• Is unsafeUseIsolateNodePortScopeForActor the right name and level of specificity?
• Is rejecting a second configured namespace per Worker the right cardinality guard?

Restricting the option to ephemeralLocal also puts it behind workerd's existing --experimental gate.

Paired workers-sdk draft: cloudflare/workers-sdk#15637

Tests

• New Node HTTP port-scope test covers cross-context dispatch with request and response bodies.
• The same test lets two IDs bind the same port and proves only the configured ID uses isolate scope.
• Existing tests confirm ordinary durable and ephemeral-local actors remain isolated.
• Server tests enforce pinning, ephemeral-local scope, and one configured actor per Worker.

[ask-bonk]

I'm Bonk, and I've done a quick review of your PR.

Adds isolate-scoped Node port tables for pinned Durable Objects.

Posted 1 inline high-severity finding.

github run

[petebacondarwin]

Closing in favour of #7357