fix(canvas): don't show "No matches" while the space sidebar is loading

[puemos]

Problem

Opening a space with a filter or search active showed the sidebar's loading skeleton and, directly underneath it, the Recent section's "No matches — Try a different search or clear the filters." empty state. Nothing had loaded yet, so the sidebar was simultaneously claiming "loading" and "we looked and found nothing".

Why: what the list shows was four independent conditions spread across the render tree, not one decision. An active filter (or an open search box) keeps the Recent section on screen by design, so it also rendered during a cold load — with nothing to show, that fell into the "No matches" branch.

Changes

Those four conditions become one listStateOf(...), so the list is "unavailable" | "loading" | "empty" | "ready" and can only be one of them. The render branches read that instead of re-deriving overlapping rules.

Two consequences worth calling out:

• Until items arrive, the existing skeleton is the only thing on screen — it stands in for pinned and recent together, rather than each section deciding for itself.
• "No matches" and "Nothing here yet" can no longer both render, which happened when a filter or search was set on a space with no items.

Deliberately nothing else: no new components, no moved files, no restyling. The rest of the file is unchanged, and #3898's context-menu wiring is untouched.

How did you test this?

Added ChannelSidebar.test.tsx covering the loading / filtered-empty / genuinely-empty states, including the reported sequence (filter active, then the list reloads). Checked that two of the five fail against the pre-fix component and pass after it.

• pnpm --filter @posthog/ui exec vitest run src/features/canvas — 40 files, 280 passed
• pnpm typecheck — 24/24 tasks
• biome check — clean

Not verified in the running app (no desktop app available in this environment).

Automatic notifications

• Publish to changelog?
• Alert Sales and Marketing teams?

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Created with PostHog Code

[trunk-io]

😎 Merged successfully - details.

[github-actions]

React Doctor found no issues in the changed files. 🎉

_{Reviewed by React Doctor for commit db03002.}

[posthog]

🦔 ReviewHog reviewed this pull request

Nothing worth raising this time, so here's a calming picture instead:

[puemos]

/trunk merge