fix(cli): sync thread ID and render clickable link on /clear (#3305)

The `/clear` slash command was resetting the conversation thread but
leaving the internal thread ID stale and rendering the new thread ID as
plain text. Bring it in line with the resumed-thread flow by
synchronizing the local thread variable and promoting the confirmation
message to a clickable link.

## Changes
- `/clear` now assigns the new thread ID to `_lc_thread_id`, preventing
the CLI from tracking a stale ID after a thread reset
- Thread reset confirmation is now scheduled for link upgrade via
`_schedule_thread_message_link`, matching the clickable thread ID
pattern used on thread resume
- Added unit test coverage validating the `/clear` command's thread ID
synchronization and UI link scheduling behavior

libs/cli/deepagents_cli/app.py

@@ -4812,13 +4812,18 @@ class DeepAgentsApp(App):
             # Reset thread to start fresh conversation
             if self._session_state:
                 new_thread_id = self._session_state.reset_thread()
+                self._lc_thread_id = new_thread_id
                 try:
                     banner = self.query_one("#welcome-banner", WelcomeBanner)
                     banner.update_thread_id(new_thread_id)
                 except NoMatches:
                     pass
-                await self._mount_message(
-                    AppMessage(f"Started new thread: {new_thread_id}")
+                thread_msg_widget = AppMessage(f"Started new thread: {new_thread_id}")
+                await self._mount_message(thread_msg_widget)
+                self._schedule_thread_message_link(
+                    thread_msg_widget,
+                    prefix="Started new thread",
+                    thread_id=new_thread_id,
                 )
         elif cmd == "/copy":
             await self._mount_message(UserMessage(command))

libs/cli/tests/unit_tests/test_app.py

@@ -2562,6 +2562,42 @@ class TestTraceCommand:
             assert isinstance(app.screen, AuthManagerScreen)
 
 
+class TestClearCommand:
+    """Test /clear slash command."""
+
+    async def test_clear_syncs_thread_id_and_schedules_link_upgrade(self) -> None:
+        """/clear should render the new ID like the resumed-thread footer."""
+        app = DeepAgentsApp(thread_id="old-thread")
+        async with app.run_test() as pilot:
+            await pilot.pause()
+            app._session_state = TextualSessionState(thread_id="old-thread")
+            app._lc_thread_id = "old-thread"
+
+            with (
+                patch("deepagents_cli.app._new_thread_id", return_value="new-thread"),
+                patch.object(app, "_schedule_thread_message_link") as schedule,
+            ):
+                await app._handle_command("/clear")
+                await pilot.pause()
+
+            assert app._session_state.thread_id == "new-thread"
+            assert app._lc_thread_id == "new-thread"
+
+            app_msgs = list(app.query(AppMessage))
+            assert any(
+                str(widget._content) == "Started new thread: new-thread"
+                for widget in app_msgs
+            )
+            schedule.assert_called_once()
+            widget = schedule.call_args.args[0]
+            assert isinstance(widget, AppMessage)
+            assert widget in app_msgs
+            assert schedule.call_args.kwargs == {
+                "prefix": "Started new thread",
+                "thread_id": "new-thread",
+            }
+
+
 class TestCopyCommand:
     """Tests for `/copy` command behavior."""