fix(hub): moderator can no longer grant admin or hard-revoke accounts

admin_patch_user was gated by require_moderator but wrote `role` and
`status` with no further check. A moderator could promote any account
(an accomplice) to admin, demote an existing admin, or set
status="revoked" — a straight path from the moderation role to full
instance control.

Split authorization by field: status between active/suspended stays
at require_moderator (reversible content moderation); role changes,
status="revoked", and touching an admin's account at all now require
user_is_admin(current_user) (new helper in deps.py, alongside the
existing require_admin/require_moderator).

Regression test: test_moderator_cannot_change_roles_or_revoke.

Third security review, finding H1.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_011pG75yGK3NthNfyjH74omG

2 files changed, 33 insertions, 5 deletions

diff --git a/packages/meshbay-hub/src/meshbay_hub/api/admin.py b/packages/meshbay-hub/src/meshbay_hub/api/admin.py
index ab6fa07..4960674 100644
--- a/packages/meshbay-hub/src/meshbay_hub/api/admin.py
+++ b/packages/meshbay-hub/src/meshbay_hub/api/admin.py
@@ -14,7 +14,7 @@ from sqlalchemy import func, select
 from sqlalchemy.ext.asyncio import AsyncSession
 
 from meshbay_hub.auth import decrypt_email
-from meshbay_hub.api.deps import require_admin, require_moderator
+from meshbay_hub.api.deps import require_admin, require_moderator, user_is_admin
 from meshbay_hub.api.revocation import get_connected_node_count, is_node_connected
 from meshbay_hub.db.engine import get_db
 from meshbay_hub.db.models import Group, GroupMember, IPLog, Node, User
@@ -196,6 +196,25 @@ async def admin_patch_user(
     if user.id == current_user.id:
         raise HTTPException(status_code=400, detail="Cannot modify your own account")
 
+    # A moderator suspends and restores accounts — reversible content moderation.
+    # Changing what someone *is* (their role), and the one irreversible status
+    # (`revoked`, which is signed and broadcast to every node), are administrative.
+    # Without this split a moderator could promote an accomplice to admin, or
+    # revoke every admin, entirely from the moderation role. `admin_delete_user`
+    # already draws this exact line for the same reason.
+    privileged = body.role is not None or body.status == "revoked"
+    if privileged and not user_is_admin(current_user):
+        raise HTTPException(
+            status_code=403,
+            detail="Changing a role, or revoking an account, requires admin rights")
+
+    # An admin's account is not a moderator's to touch at all — not their role,
+    # not their status.
+    if user_is_admin(user) and not user_is_admin(current_user):
+        raise HTTPException(
+            status_code=403,
+            detail="Only an admin can change another admin's account")
+
     from meshbay_hub.api.notifications import create_notification
 
     if body.role is not None:
diff --git a/packages/meshbay-hub/src/meshbay_hub/api/deps.py b/packages/meshbay-hub/src/meshbay_hub/api/deps.py
index 1bf57a4..907a481 100644
--- a/packages/meshbay-hub/src/meshbay_hub/api/deps.py
+++ b/packages/meshbay-hub/src/meshbay_hub/api/deps.py
@@ -72,11 +72,21 @@ async def require_user_scope(
     return current_user
 
 
+def user_is_admin(user: User) -> bool:
+    """Admin by DB role or by the config allow-list. Use inside a handler that
+    already depends on `require_moderator` but has to draw the admin line for
+    one field (see `admin_patch_user`)."""
+    return user.role == "admin" or user.username in _admin_usernames
+
+
+def user_is_moderator(user: User) -> bool:
+    return user.role in ("moderator", "admin") or user.username in _admin_usernames
+
+
 async def require_moderator(
     current_user: User = Depends(get_current_user),
 ) -> User:
-    if current_user.role not in ("moderator", "admin") \
-       and current_user.username not in _admin_usernames:
+    if not user_is_moderator(current_user):
         raise HTTPException(status_code=status.HTTP_403_FORBIDDEN,
                             detail="Moderator access required")
     return current_user
@@ -85,8 +95,7 @@ async def require_moderator(
 async def require_admin(
     current_user: User = Depends(get_current_user),
 ) -> User:
-    if current_user.role != "admin" \
-       and current_user.username not in _admin_usernames:
+    if not user_is_admin(current_user):
         raise HTTPException(status_code=status.HTTP_403_FORBIDDEN,
                             detail="Admin access required")
     return current_user