feat(hub): let a hub admin disable public groups instance-wide

A new General tab in Administration carries one switch, allow_public_groups,
stored in a hub_settings key/value table (runtime-editable, unlike hub.toml).
Default is on; an absent row means on, so an upgrade changes nothing.

Enforcement is server-side on every hub-mediated path, not just the SPA:

  - create_group        refuses visibility=public (403), staff included
  - list_public_groups  the directory returns nothing (local + federated)
  - join_group          open-joining a public group is refused
  - group_online_nodes  a non-member of a public group is handed no node
  - signaling.webrtc_offer  drops the "node hosts an open group" fallback
  - federation.export_directory  advertises nothing to peer hubs

The switch is read live, so flipping it back restores every path. Existing
members of a group that predates the switch keep their membership row and
their access — this is plan A, not a purge. GET /v1/hub/info exposes the
flag (unauthenticated) so the create-group form and the sidebar's "Public
groups" link render correctly.

Also in the admin Groups tab: a Revoke action beside Suspend. Suspend is the
reversible hub flag; Revoke calls POST /v1/admin/revoke, which sets
status=revoked and broadcasts a signed revocation every node enforces
(denylist + dropped live sessions). It is confirm-guarded and names the group.

And a message fix the revoke work surfaced: group_online_nodes, join_group and
webrtc_offer answered "Group is suspended" for any non-active status. They now
report the real state, so a member of a revoked group is told "Group is
revoked" rather than something reversible-sounding.

Tests: test_public_groups_toggle.py (10) covers the switch end to end and the
five enforcement paths; test_revocation.py gains the status-message assertion.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_018gKJ85aZyvEwarXMFzFEwi

1 files changed, 10 insertions, 4 deletions

diff --git a/packages/meshbay-hub/src/meshbay_hub/api/federation.py b/packages/meshbay-hub/src/meshbay_hub/api/federation.py
index b6b4acf..7f1262d 100644
--- a/packages/meshbay-hub/src/meshbay_hub/api/federation.py
+++ b/packages/meshbay-hub/src/meshbay_hub/api/federation.py
@@ -31,7 +31,7 @@ from sqlalchemy import select
 from sqlalchemy.ext.asyncio import AsyncSession
 
 from meshbay_common import MHP_VERSION
-from meshbay_hub import __version__
+from meshbay_hub import __version__, hub_settings
 from meshbay_hub.api.deps import require_admin
 from meshbay_hub.auth import _hub_id, _hub_sk_pem, hub_public_key_pem
 from meshbay_hub.db.engine import get_db
@@ -104,9 +104,15 @@ async def export_directory(
     except Exception as e:
         raise HTTPException(status_code=401, detail=str(e))
 
-    result = await db.execute(
-        select(Group).where(Group.visibility == "public", Group.status == "active"))
-    groups = result.scalars().all()
+    # A hub with public groups switched off advertises nothing to its peers —
+    # the local directory is empty (groups.list_public_groups), and the exported
+    # one has to match or peers keep showing groups this hub no longer serves.
+    if not await hub_settings.public_groups_allowed(db):
+        groups = []
+    else:
+        result = await db.execute(
+            select(Group).where(Group.visibility == "public", Group.status == "active"))
+        groups = result.scalars().all()
 
     return {
         "hub_id":      _hub_id,