MM-67049: Fix unauthorized access to public channels in private teams (#34886)

* do not return channels from teams a user is not a member of

* add explicit tests (clearer than adding it above)

* linting

* explicitly test incudeDeleted true and false--it was implicit before

server/channels/store/sqlstore/channel_store.go

@@ -3082,11 +3082,12 @@ func (s SqlChannelStore) Autocomplete(rctx request.CTX, userID, term string, inc
 		OrderBy("c.DisplayName").
 		Limit(model.ChannelSearchDefaultLimit)
 
+	// Always filter out soft-deleted team memberships - users removed from
+	// a team should not see channels from that team regardless of includeDeleted
+	query = query.Where(sq.Eq{"tm.DeleteAt": 0})
+
 	if !includeDeleted {
-		query = query.Where(sq.And{
-			sq.Eq{"c.DeleteAt": 0},
-			sq.Eq{"tm.DeleteAt": 0},
-		})
+		query = query.Where(sq.Eq{"c.DeleteAt": 0})
 	}
 
 	if isGuest {

server/channels/store/storetest/channel_store.go

@@ -6401,6 +6401,24 @@ func testAutocomplete(t *testing.T, rctx request.CTX, ss store.Store, s SqlStore
 		})
 	}
 
+	// MM-67049: Verify that users removed from a team cannot see channels from that
+	// team, regardless of includeDeleted. The includeDeleted parameter should only
+	// affect channel deletion status, not team membership.
+	t.Run("MM-67049: removed team member cannot see channels regardless of includeDeleted", func(t *testing.T) {
+		// Sanity check: o5 is in leftTeamID and matches search term
+		require.Equal(t, leftTeamID, o5.TeamId)
+		require.Contains(t, o5.DisplayName, "ChannelA")
+
+		// m1.UserId was removed from leftTeamID (tm5.DeleteAt was set above in the test setup)
+		for _, includeDeleted := range []bool{false, true} {
+			channels, err2 := ss.Channel().Autocomplete(rctx, m1.UserId, "ChannelA", includeDeleted, false)
+			require.NoError(t, err2)
+			for _, ch := range channels {
+				require.NotEqual(t, o5.Id, ch.Id, "includeDeleted=%v: channel from left team should not be returned", includeDeleted)
+			}
+		}
+	})
+
 	t.Run("Limit", func(t *testing.T) {
 		for i := range model.ChannelSearchDefaultLimit + 10 {
 			_, err = ss.Channel().Save(rctx, &model.Channel{