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, 44 insertions, 0 deletions

diff --git a/packages/meshbay-hub/src/meshbay_hub/hub_settings.py b/packages/meshbay-hub/src/meshbay_hub/hub_settings.py
new file mode 100644
index 0000000..280d1e2
--- /dev/null
+++ b/packages/meshbay-hub/src/meshbay_hub/hub_settings.py
@@ -0,0 +1,44 @@
+"""
+Instance-wide settings stored in the `hub_settings` table.
+
+One reader per concern, so callers never touch raw strings or key names. A
+missing row means the built-in default — an upgrade never changes behaviour on
+its own, and a downgrade that drops the table just returns to defaults.
+"""
+
+from sqlalchemy.ext.asyncio import AsyncSession
+
+from meshbay_hub.db.models import HubSetting
+
+# Whether a member may create a group that is listed in the public directory and
+# open for anyone to join. Off makes the hub private-groups-only.
+ALLOW_PUBLIC_GROUPS = "allow_public_groups"
+
+_DEFAULTS: dict[str, str] = {
+    ALLOW_PUBLIC_GROUPS: "true",
+}
+
+
+async def get_raw(db: AsyncSession, key: str) -> str | None:
+    row = await db.get(HubSetting, key)
+    return row.value if row else None
+
+
+async def set_raw(db: AsyncSession, key: str, value: str) -> None:
+    """Upsert. The caller owns the commit."""
+    row = await db.get(HubSetting, key)
+    if row:
+        row.value = value
+    else:
+        db.add(HubSetting(key=key, value=value))
+
+
+async def get_bool(db: AsyncSession, key: str) -> bool:
+    raw = await get_raw(db, key)
+    if raw is None:
+        raw = _DEFAULTS.get(key, "false")
+    return raw == "true"
+
+
+async def public_groups_allowed(db: AsyncSession) -> bool:
+    return await get_bool(db, ALLOW_PUBLIC_GROUPS)