fix(desktop): notify for the selected channel when the window is unfocused

[mdschoff]

Problem

DM and thread-reply desktop notifications are suppressed for the currently selected channel, but the check only compares channel ids — it never asks whether the app window is actually focused. Leaving a DM conversation selected and minimizing (or backgrounding) the app silently drops every notification for that conversation — the one the user is most likely waiting on. useLiveChannelUpdates.ts previously:

if (channelId === activeChannelId && !options.notifyForActiveChannel) return;

How it was implemented

• New pure predicate isSuppressedAsActiveChannel() in desktop/src/features/channels/activeChannelSuppression.ts: a channel only counts as "being viewed" when it is the active channel and the app window is focused, using the existing isAppFocused() utility from shared/lib/useDocumentVisible.ts.
• Both suppression sites in useLiveChannelUpdates.ts (the DM path and the thread-reply desktop-notification path) now share the predicate, evaluated at event-delivery time.
• The notifyForActiveChannel (notify-while-viewing) opt-in still bypasses suppression entirely, and behavior while the app is focused is unchanged.
• Regression tests in activeChannelSuppression.test.mjs, including the minimized-window case.

How to test manually

1. Open a DM conversation in the desktop app and keep it selected.
2. Minimize the app (or focus another application).
3. Have the other participant send a DM.
4. Before: no notification. After: OS notification + sound + dock bounce fire as they do for any non-active channel.
5. Re-focus the app with the DM still selected and receive another message: still suppressed (unchanged), unless the notify-while-viewing setting opts in.

No UI changes — behavior-only, so no screenshots.

Verification

• desktop: pnpm test — 5,804 pass (5 new)
• desktop: pnpm typecheck, pnpm check, pnpm build — clean

Related

Searched open PRs and issues for duplicates — none found for this specific bug. Closest neighbors: #6276 (mentions don't notify while unfocused — different mechanism, the home-feed poll pausing) and the notify-while-viewing setting added in #753. Follow-up candidate deferred to a future PR: fixing #6276 itself.

[github-actions]

🔐 Codex Security Review

Status: review required for the current range.

The current range is bc006f67087b049e2f9c4d8a2f26faceff628225...736c5eb30d867164125fb2e496dd87ef44a50297.
A new review must complete for this exact range. When manual authorization
is required, a Block organization member must comment exactly
@buzz-security-review 736c5eb30d867164125fb2e496dd87ef44a50297 to authorize a new review.
Any previous review applies only to its recorded range.