Add the socket listeners once, not once per initialize()

[cmdcolin]

Same root cause as #826 but a worse symptom: addSocketListeners registers each handler as a fresh arrow function, so socket.io cannot recognize a repeat and it does not no-op the way the addEventListener calls at the end of initialize() do — and initialize() can run more than once, since the autorun in afterAttach disposes only after the awaits either side of it and deliberately does not on failure.

A second registration means every COMMON message is submitted to the change manager twice, every connect_error raises two notifications, and every reconnect fetches the missing changes twice, so this guards on socketListenersAdded alongside the socket it belongs to; the token check throws before anything is registered, so a run that failed on it still retries cleanly.

🤖 Generated with Claude Code

https://claude.ai/code/session_01JXCNVXEZMYnkeTS6cjKYBy

[cmdcolin]

Superseded by #828 if that lands — it removes the need for this flag by separating the once-only work from the retryable work. Take either, not both.

[cmdcolin]

Closing in favour of #828, which fixes the same defect for both effects at once — it separates the once-only startup work from the retryable work, so neither the socket listeners nor the menu call needs a flag. The branch stays if anyone wants to compare.