Add error handling for default get-messages request and message parsing

[nickfujita]

Fixes issue where app crashes upon receiving a 40x response from default request to /get-messages.
Came across this while testing authentication with the agent, using the method prescribed in hono-agents

// or with authentication
app.use(
  "*",
  agentsMiddleware({
    options: {
      // onBeforeConnect: async (req) => { // original
      onBeforeRequest: async (req) => { // modified
        const token = req.headers.get("authorization");
        // validate token
        if (!token) return new Response("Unauthorized", { status: 401 });
      },
    },
  })
);

• Adds error handling to default request to /get-messages, setting the error message on the hook return object, and calling the onError callback option if provided.
• Adds the same error handling as the above in the places marked as TODO, to keep things consistent.

[changeset-bot]

🦋 Changeset detected

Latest commit: 80eee3e

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

This PR includes changesets to release 2 packages

Name	Type
agents	Patch
hono-agents	Patch

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[threepointone]

thanks for starting the PR! What do you think of my recommendation?

[threepointone]

I think it's better to actually throw the error here, and expect the user to add an ErrorBoundary

[nickfujita]

I think that might throw off many users, as it did me, because it doesn't seem to be the expected behavior for a hook to throw an error upon receiving a 40x response. For example, when using tanstack-query the standard behavior isn't to throw an error if the request fails, but rather to communicate the issue in the form of an error property on the return object, and leaving data as undefined (which maybe we should do here instead of returning an empty array 🤔).
I don't think the underlying userPartySocket requires an ErrorBoundary either, but rather communitates errors via the onerror property in it's return object.

If there was a way to provide a typescript error when using this hook without a ErrorBoundary, that would probably make it more feasible, but I'm not currently aware of a way to add that.

Maybe adding a very clear note in the documentation that there needs to be an ErrorBoundary and updating the agent template repo might prevent users from running into this, but I just can't help but feel that there would be more people filing issues for this same thing in the future 😅