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, 1 insertions, 1 deletions

diff --git a/packages/meshbay-hub/tests/harness/chat_scroll_probe.py b/packages/meshbay-hub/tests/harness/chat_scroll_probe.py
index 17ec554..5ef6c76 100644
--- a/packages/meshbay-hub/tests/harness/chat_scroll_probe.py
+++ b/packages/meshbay-hub/tests/harness/chat_scroll_probe.py
@@ -65,7 +65,7 @@ for (let i = 0; i < N; i++) {
     // grows the list the way the real thing does.
     payload: (i % 5 === 0 ? 'see https://example.invalid/p/' + i + ' ' : '')
              + 'message number ' + i + ', long enough to give the bubble a height',
-    timestamp: now - (N - i) * 60, thread_id: null,
+    timestamp: now - (N - i) * 60,
   });
 }