Replace pm2-axon with homegrown solution

[fredrikekelund]

Related issues

• Fixes STU-1301

How AI was used in this PR

I wrote the initial plan and then relied on Codex to produce the initial implementation. I've since iterated on apps/cli/lib/socket.ts over multiple rounds, touching almost every part of it. The tests are auto-generated. I've barely touched them. I've reviewed all code and manually tested Studio to ensure that site events are emitted the same as before.

Proposed Changes

In #2398, we adopted a socket-based solution for sending site events from the CLI to Studio. We opted to use the pm2-axon module for this. It's a thin library, but it offers some conveniences when working with sockets, and it was already in our dependency tree.

We've since found that pm2-axon can easily be replaced with a homegrown solution that uses modules from the Node.js standard library. This will help significantly with maintainability and long-term stability.

This PR removes the direct pm2-axon dependency in favor of apps/cli/lib/socket.ts

Testing Instructions

1. Run npm start
2. Ensure that starting and stopping sites works as expected and that the UI updates accordingly.
3. Run node apps/cli/dist/cli/main.js site start --skip-browser --path PATH_TO_SITE and ensure that the Studio UI is updated when the site starts

Pre-merge Checklist

• Have you checked for TypeScript, React or other console errors?

[wpmobilebot]

📊 Performance Test Results

Comparing 7b314fe vs trunk

site-editor

Metric	trunk	7b314fe	Diff	Change
load	1771.00 ms	1756.00 ms	-15.00 ms	⚪ 0.0%

site-startup

Metric	trunk	7b314fe	Diff	Change
siteCreation	7134.00 ms	7117.00 ms	-17.00 ms	⚪ 0.0%
siteStartup	3928.00 ms	3944.00 ms	+16.00 ms	⚪ 0.0%

---

Results are median values from multiple test runs.

Legend: 🟢 Improvement (faster) | 🔴 Regression (slower) | ⚪ No change (<50ms diff)

[bcotrim]

LGTM 👍
I didn't find any regressions!

Nit: I am not sure about the socket dependency on pm2-manager, but since that's going to be refactored in another PR it's probably not an issue anymore, I haven't reviewed #2712 yet.

[fredrikekelund]

Thanks for the review, @bcotrim 👍

I am not sure about the socket dependency on pm2-manager

Do you mean pm2-manager.ts's dependency on socket.ts?

[bcotrim]

Thanks for the review, @bcotrim 👍

I am not sure about the socket dependency on pm2-manager

Do you mean pm2-manager.ts's dependency on socket.ts?

Yes, but I think the complete solution on #2712 is cleaner and makes sense. 👍