fix(desktop): hide archived channels from #/Tab autocomplete (#6156)

🤖

## Summary

Desktop's `#`/Tab channel autocomplete offered archived channels as if
they were valid destinations. Stale channels competed with active ones
in the picker, including a confusing uppercase `STREAM` entry — the
badge of an archived stream channel leaking into the suggestion list.
After this change, autocomplete suggests only active, non-DM channels.
Links to archived channels in old messages still resolve normally.

## Demo

Before/after, real archive flow:

![Demo — archived channel disappears from #
autocomplete](https://d24qwcpro867f5.cloudfront.net/repos/buzz/prs/6156/demo-archive-autocomplete.gif)

## What changed

`useChannelLinks.ts` builds the autocomplete suggestion list from the
raw relay channel list and previously excluded only DMs, so archived
channels slipped through. The fix filters `archivedAt === null` while
generating suggestions only — the shared navigation list stays
unfiltered, so resolving historical links to archived channels is
unchanged.

- `desktop/src/features/messages/lib/useChannelLinks.ts` — suggestion
selection centralized in `selectChannelSuggestions`; excludes archived
channels and DMs; keeps the existing eight-result limit.
- `desktop/src/features/messages/lib/useChannelLinks.test.mjs` — new
tests: archived stream/forum excluded, active ones included, DMs
excluded, mixed lists.

## Validation

At exact head `5a963b8407bd48f40d992e026d0a841d2445647f`: `pnpm check`,
`pnpm typecheck`, and the full Desktop unit suite (4,960 passed). Smoke
E2E run compared against exact base `f956e6fe`: the only failures are
two pre-existing failures that reproduce on base and four documented
pass-on-retry flakes — none touches the autocomplete surface.

Signed-off-by: loganj <loganj@squareup.com>
Co-authored-by: Claude Code <noreply@anthropic.com>

desktop/src/features/messages/lib/useChannelLinks.test.mjs

@@ -0,0 +1,121 @@
+/**
+ * Unit tests for selectChannelSuggestions — the #/Tab channel-autocomplete
+ * suggestion list.
+ *
+ * Archived channels must stay resolvable in historical links elsewhere in the
+ * app, but must not be offered as new `#channel` suggestions (they were
+ * leaking through, badged STREAM/FORUM, for archived branch channels).
+ */
+
+import assert from "node:assert/strict";
+import test from "node:test";
+
+import { selectChannelSuggestions } from "./useChannelLinks.ts";
+
+function channel(overrides = {}) {
+  return {
+    id: "chan-1",
+    name: "general",
+    channelType: "stream",
+    archivedAt: null,
+    ...overrides,
+  };
+}
+
+test("excludes an archived stream channel from suggestions", () => {
+  const channels = [
+    channel({
+      id: "s1",
+      name: "shipped-feature",
+      channelType: "stream",
+      archivedAt: "2026-01-01T00:00:00Z",
+    }),
+  ];
+
+  assert.deepEqual(selectChannelSuggestions(channels, "shipped"), []);
+});
+
+test("excludes an archived forum channel from suggestions", () => {
+  const channels = [
+    channel({
+      id: "f1",
+      name: "old-rfc",
+      channelType: "forum",
+      archivedAt: "2026-01-01T00:00:00Z",
+    }),
+  ];
+
+  assert.deepEqual(selectChannelSuggestions(channels, "old"), []);
+});
+
+test("includes an active stream channel matching the query", () => {
+  const channels = [
+    channel({
+      id: "s2",
+      name: "engineering",
+      channelType: "stream",
+      archivedAt: null,
+    }),
+  ];
+
+  assert.deepEqual(selectChannelSuggestions(channels, "eng"), [
+    { id: "s2", name: "engineering", channelType: "stream" },
+  ]);
+});
+
+test("includes an active forum channel matching the query", () => {
+  const channels = [
+    channel({
+      id: "f2",
+      name: "design-rfcs",
+      channelType: "forum",
+      archivedAt: null,
+    }),
+  ];
+
+  assert.deepEqual(selectChannelSuggestions(channels, "design"), [
+    { id: "f2", name: "design-rfcs", channelType: "forum" },
+  ]);
+});
+
+test("excludes DM channels regardless of archive state", () => {
+  const channels = [
+    channel({ id: "d1", name: "alice", channelType: "dm", archivedAt: null }),
+  ];
+
+  assert.deepEqual(selectChannelSuggestions(channels, "alice"), []);
+});
+
+test("mixed list keeps only active, non-DM matches", () => {
+  const channels = [
+    channel({
+      id: "s3",
+      name: "random",
+      channelType: "stream",
+      archivedAt: null,
+    }),
+    channel({
+      id: "s4",
+      name: "random-old",
+      channelType: "stream",
+      archivedAt: "2026-01-01T00:00:00Z",
+    }),
+    channel({
+      id: "f3",
+      name: "random-forum",
+      channelType: "forum",
+      archivedAt: null,
+    }),
+    channel({
+      id: "d2",
+      name: "random-dm",
+      channelType: "dm",
+      archivedAt: null,
+    }),
+  ];
+
+  assert.deepEqual(
+    selectChannelSuggestions(channels, "random").map((s) => s.id),
+    ["s3", "f3"],
+  );
+});

desktop/src/features/messages/lib/useChannelLinks.ts

@@ -2,6 +2,7 @@ import * as React from "react";
 
 import { useChannelNavigation } from "@/shared/context/ChannelNavigationContext";
 import { detectPrefixQuery } from "@/shared/lib/detectPrefixQuery";
+import type { Channel } from "@/shared/api/types";
 import type { AutocompleteEdit } from "./useRichTextEditor";
 
 export type ChannelSuggestion = {
@@ -12,6 +13,37 @@ export type ChannelSuggestion = {
 
 const CHANNEL_QUERY_DEBOUNCE_MS = 120;
 
+/**
+ * Archived channels must stay resolvable in historical links (rendered from
+ * the unfiltered ChannelNavigationContext list), but are dead ends for new
+ * `#channel` references — exclude them here, at generation time, rather than
+ * from the shared channel list.
+ */
+function isChannelSuggestable(
+  channel: Pick<Channel, "channelType" | "archivedAt">,
+): boolean {
+  return channel.channelType !== "dm" && channel.archivedAt === null;
+}
+
+/** Exported for unit testing. */
+export function selectChannelSuggestions(
+  channels: Channel[],
+  query: string,
+): ChannelSuggestion[] {
+  const lowerQuery = query.toLowerCase();
+  return channels
+    .filter(
+      (ch) =>
+        isChannelSuggestable(ch) && ch.name.toLowerCase().includes(lowerQuery),
+    )
+    .slice(0, 8)
+    .map((ch) => ({
+      id: ch.id,
+      name: ch.name,
+      channelType: ch.channelType as "stream" | "forum",
+    }));
+}
+
 export function useChannelLinks() {
   const { channels } = useChannelNavigation();
 
@@ -27,7 +59,7 @@ export function useChannelLinks() {
 
   /** Channel names (original casing) for overlay highlighting. */
   const knownChannelNames = React.useMemo<string[]>(
-    () => channels.filter((ch) => ch.channelType !== "dm").map((ch) => ch.name),
+    () => channels.filter(isChannelSuggestable).map((ch) => ch.name),
     [channels],
   );
 
@@ -56,19 +88,7 @@ export function useChannelLinks() {
     if (channelQuery === null) {
       return [];
     }
-
-    const lowerQuery = channelQuery.toLowerCase();
-    return channels
-      .filter(
-        (ch) =>
-          ch.channelType !== "dm" && ch.name.toLowerCase().includes(lowerQuery),
-      )
-      .slice(0, 8)
-      .map((ch) => ({
-        id: ch.id,
-        name: ch.name,
-        channelType: ch.channelType as "stream" | "forum",
-      }));
+    return selectChannelSuggestions(channels, channelQuery);
   }, [channels, channelQuery]);
 
   const isChannelOpen = channelQuery !== null && channelSuggestions.length > 0;