feat: unified group management, public groups, and activity-based sidebar

Create Group wizard (Electron-only) consolidates 6 steps across 4 interfaces
into a single multi-step page: group creation on hub, node attachment, root
selection via folder picker, GEK initialization, and auto-pairing — all in one
flow. Browser SPA keeps its current behavior unchanged.

Public group support (Option A — GEK for all groups):
- All groups have GEK regardless of visibility; open-join groups auto-admit
  via TOFU when join_policy is "open"
- Key rotation blocked for public groups (API guard + UI hidden)
- Hub signaling allows WebRTC offers for nodes hosting open-join groups even
  when the caller isn't a member yet
- attach_group writes join_policy to node.toml
- Daemon loads GEK for all groups, not just private ones
- Known-device path in join_request now auto-admits to open-join groups

Node loopback API bridge (Electron IPC):
- node:detect, node:call, node:pairing-code IPC handlers in main process
- Renderer never sees tokens, paths, or keys (session token = physical access)
- platform.js node namespace for UI consumption
- Loopback endpoints: roots CRUD, member-upload toggle, reload

Bug fixes:
- Root change detection: removed premature ctx["roots"] updates from add_root
  and remove_root that prevented indexer retarget on reload
- Duplicate offline message: global fallback now gated on !group
- Signaling membership check: fallback to open-join groups for non-members

Sidebar groups sorted by last_activity_at (most recent first):
- New Group.last_activity_at column with Alembic migration
- POST /v1/groups/{id}/activity endpoint, called on connect and chat send
- Client-side sort + throttled hub updates (1/min)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

1 files changed, 16 insertions, 7 deletions

diff --git a/packages/meshbay-hub/src/meshbay_hub/api/signaling.py b/packages/meshbay-hub/src/meshbay_hub/api/signaling.py
index cb00a67..84c1167 100644
--- a/packages/meshbay-hub/src/meshbay_hub/api/signaling.py
+++ b/packages/meshbay-hub/src/meshbay_hub/api/signaling.py
@@ -90,7 +90,9 @@ async def webrtc_offer(
     if not ws:
         raise HTTPException(status_code=404, detail="Node not connected")
 
-    # The caller must share at least one active group with the target node.
+    # The caller must share at least one active group with the target node,
+    # OR the node must host at least one open-join group (public groups admit
+    # anyone — the node's MNP handshake handles authorization).
     node_group_ids = set(_node_groups.get(node_id, []))
     if node_group_ids:
         result = await db.execute(
@@ -100,12 +102,19 @@ async def webrtc_offer(
             ))
         shared = [gid for (gid,) in result.all()]
         if not shared:
-            raise HTTPException(status_code=403, detail="Not a member of any group on this node")
-
-        active = await db.execute(
-            select(Group.id).where(Group.id.in_(shared), Group.status == "active"))
-        if not active.first():
-            raise HTTPException(status_code=403, detail="Group is not active")
+            has_open = await db.execute(
+                select(Group.id).where(
+                    Group.id.in_(node_group_ids),
+                    Group.join_policy == "open",
+                    Group.status == "active",
+                ))
+            if not has_open.first():
+                raise HTTPException(status_code=403, detail="Not a member of any group on this node")
+        else:
+            active = await db.execute(
+                select(Group.id).where(Group.id.in_(shared), Group.status == "active"))
+            if not active.first():
+                raise HTTPException(status_code=403, detail="Group is not active")
 
     if _pending_per_user.get(current_user.id, 0) >= MAX_PENDING_PER_USER:
         raise HTTPException(status_code=429, detail="Too many pending connections")