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, 10 insertions, 8 deletions

diff --git a/packages/meshbay-node/tests/test_chat_is_bounded.py b/packages/meshbay-node/tests/test_chat_is_bounded.py
index c48f26d..f98fd81 100644
--- a/packages/meshbay-node/tests/test_chat_is_bounded.py
+++ b/packages/meshbay-node/tests/test_chat_is_bounded.py
@@ -210,10 +210,10 @@ async def test_one_member_at_their_limit_has_not_spent_anyone_elses(ctx, store):
 
 async def test_the_clear_fields_are_what_they_claim_and_no_larger(ctx, store):
     """
-    `sender_name` and `thread_id` travel in clear beside the sealed envelope,
-    which carries its own. They are stored on the operator's disk and relayed
-    to every member, so a megabyte of name or a list for a thread id is dropped,
-    not kept.
+    `sender_name` travels in clear beside the sealed envelope, which carries its
+    own. It is stored on the operator's disk and relayed to every member, so a
+    megabyte of name is dropped, not kept — and a `thread_id`, which an older
+    client still sends, is neither.
     """
     alice = _session(ctx, store, user="alice", conn="c1")
     bob = _session(ctx, store, user="bob", conn="c2")
@@ -225,17 +225,19 @@ async def test_the_clear_fields_are_what_they_claim_and_no_larger(ctx, store):
 
     stored = (await store.get_recent(limit=1))[0]
     assert stored.sender_name in ("", None)
-    assert stored.thread_id is None
     relayed = [m for m in bob.sent if m.get("type") == "chat_msg"]
-    assert relayed and relayed[-1]["sender_name"] == "" and relayed[-1]["thread_id"] is None
+    assert relayed and relayed[-1]["sender_name"] == "" and "thread_id" not in relayed[-1]
 
 
-async def test_ordinary_clear_fields_pass_unchanged(ctx, store):
+async def test_an_older_clients_message_is_taken_its_thread_id_ignored(ctx, store):
     alice = _session(ctx, store, user="alice", conn="c1")
+    bob = _session(ctx, store, user="bob", conn="c2")
     msg = _message(alice, size=64)
     msg["sender_name"] = "Alice"
     msg["thread_id"] = "42"
     alice._do_chat_message(msg)
     await _drain(ctx)
     stored = (await store.get_recent(limit=1))[0]
-    assert (stored.sender_name, stored.thread_id) == ("Alice", "42")
+    assert stored.sender_name == "Alice"
+    relayed = [m for m in bob.sent if m.get("type") == "chat_msg"]
+    assert relayed and "thread_id" not in relayed[-1]