computer: Give host module calls an execution id, log and defer

[mattzcarey]

Every host module call's context now has executionId, log(text) and defer(fn). A module can keep state for one run, clean it up when the run ends, and tell the caller things its return value can't carry.

agents/browser is moving off @cloudflare/codemode to become a host module (ws:browser) that exec code imports. Its CDP connector needs three things host modules didn't have:

• an id to keep one browser socket per run;
• a hook to save the active tab and close the socket when the run ends;
• a place to say "the browser was restarted" or "the page opened a new tab", which codemode added to the tool result. exec's result belongs to Computer, so the module writes those lines to standard error.

modules: {
  "ws:remote": {
    async send([message], context) {
      let socket = sockets.get(context.executionId);
      if (!socket) {
        socket = await openSocket();
        sockets.set(context.executionId, socket);
        context.defer(() => {
          sockets.delete(context.executionId);
          socket.close();
        });
      }
      return socket.send(message);
    },
  },
}

Deferred functions run however the run ends. They start after the code has finished and its host calls have settled, and finish before the result is published, so the next run sees what they saved. They run one at a time, last registered first, each within the host call deadline. A failure is reported on standard error and the rest still run. Log lines have their own maxStdioBytes budget. docs/17_isolate_javascript.md covers this under host modules.

npm test in packages/computer and npm run check ran. New workerd tests cover the id, logging, and deferred functions on success, failure, cancellation and a throwing deferred function. The deferred tests fail with runDeferred turned off.

This touches bridge.ts and the hand-built test contexts that #238 also changes, so whichever lands second needs a small rebase. Under #238's replay, a deferred function should run once, on the attempt that settles.

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🦋 Changeset detected

Latest commit: 2dbb36a

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

This PR includes changesets to release 4 packages

Name	Type
@cloudflare/computer	Minor
@cloudflare/dofs	Minor
@cloudflare/computer-rpc	Minor
@cloudflare/computerd	Minor

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commit: 2dbb36a