feat: let the operator purge a group's chat (MNP 6.1)

Signed chat_purge from the Chat settings deletes every stored message;
epoch keys and attachments stay. The ack is broadcast so open chat
panels empty.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

3 files changed, 43 insertions, 1 deletions

diff --git a/packages/meshbay-node/src/meshbay_node/transport/webrtc/admin.py b/packages/meshbay-node/src/meshbay_node/transport/webrtc/admin.py
index 48734ab..7b3b1c9 100644
--- a/packages/meshbay-node/src/meshbay_node/transport/webrtc/admin.py
+++ b/packages/meshbay-node/src/meshbay_node/transport/webrtc/admin.py
@@ -15,6 +15,7 @@ from meshbay_common.adminop import (
     OP_CHAT_DIRECTORY,
     OP_CHAT_EPOCH,
     OP_CHAT_LINK_PREVIEW,
+    OP_CHAT_PURGE,
     OP_DIR_DELETE,
     OP_FILE_DELETE,
     OP_INVITE_CANCEL,
@@ -68,6 +69,7 @@ _ADMIN_EXECUTORS = {
     OP_CHAT_LINK_PREVIEW: "_admin_exec_chat_link_preview",
     OP_SEARCH_LISTED: "_admin_exec_search_listed",
     OP_CHAT_EPOCH: "_admin_exec_chat_epoch",
+    OP_CHAT_PURGE: "_admin_exec_chat_purge",
     OP_ROOT_EJECT: "_admin_exec_root_eject",
     OP_ROOT_PLUG: "_admin_exec_root_plug",
 }
diff --git a/packages/meshbay-node/src/meshbay_node/transport/webrtc/chat.py b/packages/meshbay-node/src/meshbay_node/transport/webrtc/chat.py
index dc43ae2..f200884 100644
--- a/packages/meshbay-node/src/meshbay_node/transport/webrtc/chat.py
+++ b/packages/meshbay-node/src/meshbay_node/transport/webrtc/chat.py
@@ -7,7 +7,12 @@ import time
 
 import blake3
 from meshbay_common import MNP_VERSION
-from meshbay_common.adminop import OP_CHAT_DIRECTORY, OP_CHAT_EPOCH, OP_CHAT_LINK_PREVIEW
+from meshbay_common.adminop import (
+    OP_CHAT_DIRECTORY,
+    OP_CHAT_EPOCH,
+    OP_CHAT_LINK_PREVIEW,
+    OP_CHAT_PURGE,
+)
 from meshbay_common.chatbox import NONCE_LEN as CHAT_NONCE_LEN
 from meshbay_common.chatbox import SIG_LEN as CHAT_SIG_LEN
 from meshbay_common.groupbox import PURPOSE_CHAT_KEYS, seal
@@ -227,6 +232,40 @@ class ChatMixin:
         self._broadcast_to_group({"type": MNP.CHAT_EPOCH_ACK,
                                   "v": MNP_VERSION, "epoch": result["epoch"]})
 
+    def _do_chat_purge(self, msg: dict) -> None:
+        """
+        Delete the group's stored chat. Operator only, and signed. The subject is
+        the group id, so a signature for one group's purge purges no other.
+
+        Always this connection's group, never one named in the message: the ack
+        is broadcast to this group, and an operator purges the chat they see.
+        """
+        group_id = self._group_id
+        if not group_id:
+            self._send({"type": "error", "detail": "No group on this connection"})
+            return
+        if not self._has_admin_authority():
+            self._send({"type": "error", "detail": "No authorized key for this"})
+            return
+        self._issue_admin_challenge(OP_CHAT_PURGE, group_id, group_id=group_id)
+
+    async def _admin_exec_chat_purge(
+        self, pending: dict, transcript: bytes, sig: bytes,
+    ) -> None:
+        if not await self._verify_admin_sig(transcript, sig):
+            self._send({"type": "error", "detail": "Signature verification failed"})
+            self._audit("admin_auth_failed", f"chat_purge:{pending['subject'][:8]}")
+            return
+        try:
+            result = await self._run_op(ops.purge_chat, pending["subject"])
+        except ops.OpError as e:
+            self._send({"type": "error", "detail": e.message})
+            return
+        self._audit("chat_purge", str(result["removed"]))
+        # Every open chat panel empties, not only the operator's.
+        self._broadcast_to_group({"type": MNP.CHAT_PURGE_ACK,
+                                  "v": MNP_VERSION, "removed": result["removed"]})
+
     async def _do_chat_keys_req(self, msg: dict) -> None:
         """
         Hand this member every chat epoch key the group has, sealed.
diff --git a/packages/meshbay-node/src/meshbay_node/transport/webrtc/dispatch.py b/packages/meshbay-node/src/meshbay_node/transport/webrtc/dispatch.py
index a8b5767..5d4ed94 100644
--- a/packages/meshbay-node/src/meshbay_node/transport/webrtc/dispatch.py
+++ b/packages/meshbay-node/src/meshbay_node/transport/webrtc/dispatch.py
@@ -56,6 +56,7 @@ _HANDLERS = {
     MNP.CHAT_LINK_PREVIEW: ("_do_chat_link_preview", INLINE),
     MNP.SEARCH_LISTED: ("_do_search_listed", INLINE),
     MNP.CHAT_EPOCH: ("_do_chat_epoch", INLINE),
+    MNP.CHAT_PURGE: ("_do_chat_purge", INLINE),
     MNP.CHAT_KEYS_REQ: ("_do_chat_keys_req", SPAWNED),
     MNP.GROUP_ROSTER_REQ: ("_do_group_roster_req", SPAWNED),
     MNP.MEDIA_META_REQ: ("_do_media_meta_request", SPAWNED),