[backport/1.4] Improve frontend: only get Kernel/Journal when needed

[joaoantoniocardoso]

This is a backport of #4025 into 1.4.

[github-actions]

Automated PR Review

0. Summary

• Verdict: MINOR SUGGESTIONS ✏️

Backports #4025 to 1.4-dev: the kernel-buffer WebSocket is no longer opened eagerly at module load; instead Kernel.vue's mounted() / beforeDestroy() hooks refcount subscribers via new subscribeKernelMessages / unsubscribeKernelMessages helpers, and SystemInformationView.vue only mounts the currently-active tab so the socket actually tears down when the user leaves. Journal.vue is deliberately not touched here — it does not yet exist on 1.4-dev, which explains the "Kernel/Journal" wording in the title.

6. Code Quality & Style

• 6.1 [minor] core/frontend/src/store/system-information.ts — two spots now contain two consecutive blank lines, which will trip airbnb's no-multiple-empty-lines (max: 1) and fail yarn --cwd core/frontend lint:

  • Between the new updateModel mutation and updateNetstat (the + blank line at diff hunk 2 / around post-image line ~95).
  • Between updateSystemUnixTimeSeconds and fetchModel after removing fetchKernelMessage — the two surrounding blank lines were left in place (diff hunk 3, around post-image line ~184).

  yarn --cwd core/frontend lint --fix will collapse both.

8. Documentation

• 8.1 [nit] core/frontend/src/store/system-information.ts — the replacement comment ("Vuex store modules are a poor fit for WebSocket callbacks; keep sockets outside the store and open them only while a UI consumer is mounted (Kernel tab).") is a solid improvement over the previous "It appears that the store is incompatible..." — reads as a real explanation of the why.

9. Nitpicks / Optional

• 9.1 [nit] core/frontend/src/views/SystemInformationView.vue:82 — page_selected: 0 as number changes the initial selected tab from "none" (null) to the first tab (Processes). This is required for the new <template v-if="page_selected === index"> gate to render anything on first paint, and matches Vuetify's implicit numeric v-model on <v-tabs> with no explicit :value per tab, so it's the correct fix — just calling out that it's a subtle user-visible behavior change worth eyeballing on 1.4-dev.
• 9.2 [nit] Conditionally mounting only the active tab (the <template v-if> wrap) means per-tab local state (scroll position, filter fields, transient UI state in Processes/Network/Firmware) is now discarded on every tab switch. That's an intentional tradeoff for tearing down the kernel WS, but a maintainer should be aware of it since the previous behavior kept all six tabs alive.

Generated by PR Review Bot. This is advisory, a human reviewer must still approve.