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>

11 files changed, 64 insertions, 66 deletions

diff --git a/packages/meshbay-cli/src/meshbay_cli/client/chat.py b/packages/meshbay-cli/src/meshbay_cli/client/chat.py
index 587303a..d525abf 100644
--- a/packages/meshbay-cli/src/meshbay_cli/client/chat.py
+++ b/packages/meshbay-cli/src/meshbay_cli/client/chat.py
@@ -186,7 +186,7 @@ async def post(session: GroupSession, keys: ChatKeys, text: str, sender_name: st
     ident = session.identity
     device_b64 = ident.pk_ed
     sealed = seal(key, session.group_id, epoch, device_b64, unb64(device_b64), ident.sk_ed,
-                  {"text": text, "thread_id": None, "sender_name": sender_name,
+                  {"text": text, "sender_name": sender_name,
                    "sent_at": int(time.time())})
     if len(sealed["ct"]) > MAX_CIPHERTEXT:
         raise CliError(USAGE, "This message is too large for chat; send it as a file "
@@ -195,5 +195,5 @@ async def post(session: GroupSession, keys: ChatKeys, text: str, sender_name: st
                               "format": FORMAT_SEALED, "epoch": epoch,
                               "ct": sealed["ct"], "nonce": sealed["nonce"],
                               "device": unb64(device_b64), "sig": sealed["sig"],
-                              "thread_id": None, "sender_name": None}, "ack")
+                              "sender_name": None}, "ack")
 
diff --git a/packages/meshbay-cli/tests/fake_node.py b/packages/meshbay-cli/tests/fake_node.py
index 552bd39..c618ee4 100644
--- a/packages/meshbay-cli/tests/fake_node.py
+++ b/packages/meshbay-cli/tests/fake_node.py
@@ -140,7 +140,7 @@ class FakeNode:
     def _store(self, device: bytes, epoch: int, sealed: dict, sender_id: str) -> None:
         self.chat.append({"id": len(self.chat) + 1, "sender_id": sender_id,
                           "sender_name": "", "timestamp": 1_700_000_000 + len(self.chat),
-                          "thread_id": None, "format": 1, "epoch": epoch,
+                          "format": 1, "epoch": epoch,
                           "device": device, "nonce": sealed["nonce"], "sig": sealed["sig"],
                           "payload": "", "ct": sealed["ct"]})
 
diff --git a/packages/meshbay-common/tests/test_js_python_parity.py b/packages/meshbay-common/tests/test_js_python_parity.py
index bb52742..8f7f7b9 100644
--- a/packages/meshbay-common/tests/test_js_python_parity.py
+++ b/packages/meshbay-common/tests/test_js_python_parity.py
@@ -497,7 +497,7 @@ const toHex = (u8) =>
 
 def _chat_payload(idx: int) -> dict:
     """A distinct message per vector, so a crossed result cannot pass."""
-    return {"text": f"message {idx} — café", "thread_id": None,
+    return {"text": f"message {idx} — café",
             "sender_name": f"member-{idx}", "sent_at": 1_700_000_000 + idx}
 
 
diff --git a/packages/meshbay-hub/src/meshbay_hub/static/chat-app.js b/packages/meshbay-hub/src/meshbay_hub/static/chat-app.js
index 1d61c43..34e86eb 100644
--- a/packages/meshbay-hub/src/meshbay_hub/static/chat-app.js
+++ b/packages/meshbay-hub/src/meshbay_hub/static/chat-app.js
@@ -472,7 +472,7 @@ function ChatPanel({ transportRef, username, userId, entries, gekRef,
     setSending(true);
     setInput('');
     try {
-      await transport.sendChat(text, 0, null, username);
+      await transport.sendChat(text, 0, username);
       setMessages(prev => [...prev, {
         id: `own-${Date.now()}-${Math.random().toString(36).slice(2)}`,
         own: true,
@@ -480,7 +480,6 @@ function ChatPanel({ transportRef, username, userId, entries, gekRef,
         sender_name: username,
         payload: text,
         timestamp: Date.now() / 1000,
-        thread_id: null,
       }]);
       jumpToBottom();
       if (onActivity) onActivity();
@@ -515,11 +514,11 @@ function ChatPanel({ transportRef, username, userId, entries, gekRef,
       const structured = JSON.stringify({
         text: '', attachment: { filename: storedAs, size: file.size, type: ftype },
       });
-      await transport.sendChat(structured, 0, null, username);
+      await transport.sendChat(structured, 0, username);
       setMessages(prev => [...prev, {
         id: `own-${Date.now()}-${Math.random().toString(36).slice(2)}`,
         own: true, sender_id: userId || username, sender_name: username,
-        payload: structured, timestamp: Date.now() / 1000, thread_id: null,
+        payload: structured, timestamp: Date.now() / 1000,
       }]);
       jumpToBottom();
     } catch (err) {
diff --git a/packages/meshbay-hub/src/meshbay_hub/static/transport-chat.js b/packages/meshbay-hub/src/meshbay_hub/static/transport-chat.js
index 9ce07bc..3efbb22 100644
--- a/packages/meshbay-hub/src/meshbay_hub/static/transport-chat.js
+++ b/packages/meshbay-hub/src/meshbay_hub/static/transport-chat.js
@@ -138,7 +138,6 @@ extendTransport(class {
       sender_id: row.sender_id,
       sender_name: row.sender_name || '',
       timestamp: row.timestamp,
-      thread_id: row.thread_id,
     };
     const format = row.format || 0;
     if (format === 0) {
@@ -169,7 +168,7 @@ extendTransport(class {
    * post in clear into a group whose members believe their chat is encrypted;
    * the node refuses it too, and the two refusals agreeing is the point.
    */
-  async sendChat(text, iteration, threadId, senderName) {
+  async sendChat(text, iteration, senderName) {
     const keys = await this.chatKeys();
     const epoch = this.chatEpoch || keys.current;
     const epochKey = keys.byEpoch.get(epoch);
@@ -182,7 +181,6 @@ extendTransport(class {
     const gid = this._groupId || '';
     const plaintext = msgpack_encode({
       text: String(text),
-      thread_id: threadId || null,
       sender_name: senderName || '',
       sent_at: Math.floor(Date.now() / 1000),
     });
@@ -204,7 +202,6 @@ extendTransport(class {
       nonce,
       device,
       sig,
-      thread_id: threadId || null,
       // Deliberately absent: the display name is inside the envelope now.
       sender_name: null,
     });
@@ -315,7 +312,6 @@ extendTransport(class {
         ...base,
         payload: String(plain.text || ''),
         sender_name: plain.sender_name || base.sender_name,
-        thread_id: plain.thread_id ?? base.thread_id,
         device: deviceB64,
         verified: true,
         trust,
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,
   });
 }
 
diff --git a/packages/meshbay-node/src/meshbay_node/chat/store.py b/packages/meshbay-node/src/meshbay_node/chat/store.py
index 9e07aff..7610b33 100644
--- a/packages/meshbay-node/src/meshbay_node/chat/store.py
+++ b/packages/meshbay-node/src/meshbay_node/chat/store.py
@@ -54,8 +54,11 @@ CREATE TABLE IF NOT EXISTS messages (
     sender_name TEXT DEFAULT ''
 );
 CREATE INDEX IF NOT EXISTS idx_messages_ts ON messages(timestamp);
-CREATE INDEX IF NOT EXISTS idx_messages_thread ON messages(thread_id);
 """
+# `thread_id` is written and read by nothing: chat has no threads. The column
+# stays, empty, because a node downgraded to an older version names it in every
+# query, and its rows must keep opening. Its index goes; an older node makes it
+# again on its own.
 
 # Additive, every one with a default, so an existing chat.db opens unchanged and
 # a node that is downgraded still reads its own rows. `CREATE TABLE IF NOT
@@ -88,7 +91,6 @@ class StoredMessage:
     iteration: int
     payload: bytes
     timestamp: float
-    thread_id: str | None
     sender_name: str = ""
     format: int = FORMAT_PLAIN
     epoch: int = 0
@@ -97,16 +99,16 @@ class StoredMessage:
     sig: bytes | None = None
 
 
-_COLUMNS = ("id, sender_id, iteration, payload, timestamp, thread_id, "
+_COLUMNS = ("id, sender_id, iteration, payload, timestamp, "
             "sender_name, format, epoch, device, nonce, sig")
 
 
 def _row(r) -> StoredMessage:
     return StoredMessage(
         id=r[0], sender_id=r[1], iteration=r[2], payload=r[3],
-        timestamp=r[4], thread_id=r[5], sender_name=r[6] or "",
-        format=r[7] or FORMAT_PLAIN, epoch=r[8] or 0,
-        device=r[9], nonce=r[10], sig=r[11],
+        timestamp=r[4], sender_name=r[5] or "",
+        format=r[6] or FORMAT_PLAIN, epoch=r[7] or 0,
+        device=r[8], nonce=r[9], sig=r[10],
     )
 
 
@@ -132,6 +134,7 @@ class ChatStore:
                 # nothing to show for it.
                 pass
         await self._db.execute(_REPLAY_INDEX)
+        await self._db.execute("DROP INDEX IF EXISTS idx_messages_thread")
         await self._db.commit()
 
     async def close(self) -> None:
@@ -151,7 +154,6 @@ class ChatStore:
         sender_id: str,
         iteration: int,
         payload: bytes,
-        thread_id: str | None = None,
         sender_name: str = "",
         *,
         format: int = FORMAT_PLAIN,
@@ -171,9 +173,9 @@ class ChatStore:
         try:
             cursor = await self._db.execute(
                 "INSERT INTO messages (sender_id, iteration, payload, timestamp, "
-                " thread_id, sender_name, format, epoch, device, nonce, sig) "
-                "VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?)",
-                (sender_id, iteration, payload, ts, thread_id, sender_name,
+                " sender_name, format, epoch, device, nonce, sig) "
+                "VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?)",
+                (sender_id, iteration, payload, ts, sender_name,
                  format, epoch, device, nonce, sig),
             )
         except aiosqlite.IntegrityError as e:
@@ -234,16 +236,6 @@ class ChatStore:
             "SELECT 1 FROM messages WHERE id < ? LIMIT 1", (message_id,))
         return await cursor.fetchone() is not None
 
-    async def get_thread(self, thread_id: str, limit: int = 100) -> list[StoredMessage]:
-        """Get messages in a thread."""
-        cursor = await self._db.execute(
-            f"SELECT {_COLUMNS} "
-            "FROM messages WHERE thread_id = ? ORDER BY timestamp ASC LIMIT ?",
-            (thread_id, limit),
-        )
-        rows = await cursor.fetchall()
-        return [_row(r) for r in rows]
-
     @property
     def db_path(self) -> Path:
         """Where this store lives — the re-encryption command backs it up."""
diff --git a/packages/meshbay-node/src/meshbay_node/ops/chat.py b/packages/meshbay-node/src/meshbay_node/ops/chat.py
index 9fc7b94..7caf85c 100644
--- a/packages/meshbay-node/src/meshbay_node/ops/chat.py
+++ b/packages/meshbay-node/src/meshbay_node/ops/chat.py
@@ -214,7 +214,6 @@ async def encrypt_chat_history(state: dict, group_id: str) -> dict:
                 if isinstance(row.payload, bytes) else str(row.payload))
         env = seal(key, group_id, epoch, device_b64, device_raw, sk_node, {
             "text": text,
-            "thread_id": row.thread_id,
             "sender_name": row.sender_name,
             "sent_at": int(row.timestamp),
             # The node sealed this after the fact; it did not witness it being
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,
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]
diff --git a/packages/meshbay-node/tests/test_chat_store.py b/packages/meshbay-node/tests/test_chat_store.py
index 2533921..c4dff6d 100644
--- a/packages/meshbay-node/tests/test_chat_store.py
+++ b/packages/meshbay-node/tests/test_chat_store.py
@@ -28,7 +28,6 @@ async def test_save_and_retrieve(store):
     assert msgs[0].sender_id == "alice"
     assert msgs[0].iteration == 0
     assert msgs[0].payload == b"hello"
-    assert msgs[0].thread_id is None
 
 
 @pytest.mark.asyncio
@@ -52,15 +51,32 @@ async def test_get_messages_since(store):
 
 
 @pytest.mark.asyncio
-async def test_thread_messages(store):
-    await store.save_message("alice", 0, b"root", thread_id="t1")
-    await store.save_message("bob", 1, b"reply", thread_id="t1")
-    await store.save_message("carol", 2, b"other")
-
-    thread = await store.get_thread("t1")
-    assert len(thread) == 2
-    assert thread[0].sender_id == "alice"
-    assert thread[1].sender_id == "bob"
+async def test_the_thread_column_stays_for_an_older_node_and_its_index_goes(tmp_path):
+    """Chat has no threads; a node downgraded to a version that still names
+    `thread_id` in every query must keep reading its rows."""
+    import sqlite3
+    path = tmp_path / "chat.db"
+    with sqlite3.connect(path) as c:                 # as an older node left it
+        c.executescript("""
+            CREATE TABLE messages (id INTEGER PRIMARY KEY AUTOINCREMENT,
+                sender_id TEXT NOT NULL, iteration INTEGER NOT NULL,
+                payload BLOB NOT NULL, timestamp REAL NOT NULL,
+                thread_id TEXT DEFAULT NULL, sender_name TEXT DEFAULT '');
+            CREATE INDEX idx_messages_thread ON messages(thread_id);
+            INSERT INTO messages (sender_id, iteration, payload, timestamp, thread_id)
+                VALUES ('alice', 0, X'6869', 1.0, 't1');""")
+    s = ChatStore(path)
+    await s.open()
+    await s.save_message("bob", 1, b"now")
+    assert [m.payload for m in await s.get_recent()] == [b"hi", b"now"]
+    await s.close()
+    with sqlite3.connect(path) as c:
+        assert "thread_id" in [r[1] for r in c.execute("PRAGMA table_info(messages)")]
+        assert not c.execute("SELECT 1 FROM sqlite_master WHERE name = "
+                             "'idx_messages_thread'").fetchone()
+        # What an older node selects still answers.
+        assert c.execute("SELECT thread_id FROM messages ORDER BY id").fetchall() == [
+            ("t1",), (None,)]
 
 
 @pytest.mark.asyncio