Fix: Chat member sidebar shows space members, not room

[mjkatgithub]

Planning

• Size: S
• Estimate: 2 SP

Goal

When a user opens a channel inside a space (e.g. #general), the right-hand member sidebar must list and count only joined members of that room — like Element, Cinny, and Sable.

Today it shows a deduplicated union of members across the whole space (space room + all visible child channels), which inflates the count (~1780 vs ~743) and can hide room-only members (e.g. bots present only in that channel).

Root cause (confirmed in code)

In app/pages/chat.vue:

<ChatMemberList
  v-else-if="selectedSpaceIdRef && spaceMemberGroups.length > 0"
  :grouped-members="spaceMemberGroups"
/>
<ChatMemberList v-else :members="memberItems" />

• memberItems — correct: selectedRoom.getMembers() for the active room.
• spaceMemberGroups — from useSpaceMembers, which iterates rootSpaceId + all visibleRoomsForSidebar IDs, dedupes by userId, and applies space-level custom roles.

Whenever a space is selected and roles exist, the space aggregate wins; room members are never shown.

Scope

• Right sidebar (members panel) uses active selectedRoomId membership when a room is open.
• Member count label reflects that room (joined members only).
• Grouping: prefer room power levels / Matrix roles for channels (align with Element); space custom roles may remain for space-only views or settings — define in implementation.
• Include all joined room members (bots, guests with join, etc.).
• Home / DM rooms: keep existing memberItems behavior.

Out of scope

• Space-wide member browser (could be a separate space-settings or “space members” view later).
• Performance work (Perf: Chat-Laufzeit — scoped computeds und Sidebar-Updates #103).

Branch

bug/chat-room-member-list

Acceptance criteria

• In a large space channel (e.g. Morpheus #general): count matches Element (~700s), not root space (~1780).
• Room-only bots/users appear in the list (e.g. both bots when both are joined in that room).
• Switching channels updates list and count immediately.
• DMs and Home group chats unchanged.

Test checklist

Unit

• Member list source selects room vs space based on selectedRoomId + context.
• Count equals joined members on mocked Room.getMembers().

Manual

• Compare #general member count with Element.
• Verify both room bots visible when joined in room.
• Switch channel → list updates.

Related

• Feature: Space settings and structure management #23 — space member groups (settings/sidebar); do not reuse for per-room chat sidebar.
• Reported while validating Perf: Chat-Laufzeit — scoped computeds und Sidebar-Updates #103 on Morpheus Community Matrix.

Epic

Sub-issue of #3 (Phase 3).