refactor(chat): no thread_id — chat has no threads

Nothing ever set it (the page and the CLI sent null) and nothing read it
(the node's get_thread had no caller). It is no longer sent by the page or
the CLI, in clear or in the sealed payload, nor relayed or served by the
node; get_thread and its index are gone, and the protocol and design docs
no longer name it.

The node still accepts a chat_msg carrying one, from the desktop apps and
CLIs already installed, and drops it. The column stays, empty, in chat.db:
a node downgraded to an older version names it in every query.

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

1 files changed, 7 insertions, 13 deletions

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 ed2c43a..5bc9dbb 100644
--- a/packages/meshbay-node/src/meshbay_node/transport/webrtc/chat.py
+++ b/packages/meshbay-node/src/meshbay_node/transport/webrtc/chat.py
@@ -75,7 +75,7 @@ _LINK_PREVIEW_RATE_NODE = 60
 # C5a; this is the same question asked of the path nobody had asked it of.
 #
 # 64 KB of ciphertext is about sixty thousand characters. The sealed payload is
-# the text, a thread id, a display name and a timestamp: an attachment is a file
+# the text, a display name and a timestamp: an attachment is a file
 # on a root and travels as a reference (§4.5), so nothing legitimate comes close.
 MAX_CHAT_CIPHERTEXT = 64 * 1024
 # Per account per group, not per connection: a second tab does not make a person
@@ -330,18 +330,14 @@ class ChatMixin:
         # anyone on the node.
         gctx = self._group_ctx()
         chat_store = gctx.get("chat_store")
-        # The two fields that travel in clear beside the ciphertext (the sealed
-        # envelope carries its own). Stored and relayed to every member, so they
-        # are what they claim to be and no larger: a name as long as a username,
-        # a thread id as long as a message id. Anything else is dropped.
+        # The one field that travels in clear beside the ciphertext (the sealed
+        # envelope carries its own). Stored and relayed to every member, so it is
+        # what it claims to be and no larger: a name as long as a username.
+        # Anything else is dropped. A `thread_id` from an older client is
+        # ignored: chat has no threads.
         sender_name = msg.get("sender_name", "")
         if not isinstance(sender_name, str) or len(sender_name) > 64:
             sender_name = ""
-        thread_id = msg.get("thread_id")
-        id_like = (isinstance(thread_id, int) and not isinstance(thread_id, bool)
-                   or isinstance(thread_id, str) and len(thread_id) <= 64)
-        if thread_id is not None and not id_like:
-            thread_id = None
 
         # Two shapes, and keeping them apart is what makes this deployable.
         #
@@ -387,7 +383,7 @@ class ChatMixin:
             self._spawn(self._store_chat_message(
                 chat_store,
                 iteration=msg.get("iteration", 0), payload=raw,
-                thread_id=thread_id, sender_name=sender_name,
+                sender_name=sender_name,
                 format=fmt, epoch=epoch, device=device, nonce=nonce, sig=sig,
             ))
 
@@ -398,7 +394,6 @@ class ChatMixin:
             "sender_id": self._user_id,
             "sender_name": sender_name,
             "payload": payload,
-            "thread_id": thread_id,
             "timestamp": time.time(),
             "format": fmt,
             "epoch": epoch,
@@ -613,7 +608,6 @@ class ChatMixin:
             "sender_id": m.sender_id,
             "sender_name": m.sender_name or names.get(m.sender_id, ""),
             "timestamp": m.timestamp,
-            "thread_id": m.thread_id,
             "format": m.format,
             "epoch": m.epoch,
             "device": m.device,