fix(cli): preserve startup banner on terminal resize

Recover from SIGWINCH without clearing the physical screen or scrollback
buffer. The startup banner and tool summary are printed before
prompt_toolkit owns the live chrome, so they live in normal terminal
scrollback. Calling erase_screen() + \x1b[3J] on every resize removed
that UI permanently — _replay_output_history cannot reconstruct it
because the banner was never added to _OUTPUT_HISTORY.

Instead, just reset prompt_toolkit's renderer cache and invalidate so
the next incremental redraw starts from a clean slate, then let the
original on_resize handler recalculate layout for the new terminal
size. This matches the behaviour of bash/zsh/fish on SIGWINCH.

Fixes NousResearch/hermes-agent#22999

tests/cli/test_cli_force_redraw.py

@@ -71,32 +71,32 @@ class TestForceFullRedraw:
             "invalidate",
         ]
 
-    def test_resize_rebuilds_scrollback_before_prompt_toolkit_redraw(self, bare_cli, monkeypatch):
+    def test_resize_preserves_scrollback_and_resets_renderer(self, bare_cli, monkeypatch):
+        """Resize recovery must NOT erase screen or scrollback.
+
+        The startup banner lives in normal terminal scrollback (printed
+        before prompt_toolkit owns the chrome).  Clearing scrollback on
+        SIGWINCH removes it and ``_replay_output_history`` cannot
+        reconstruct it.  The fix is to only reset the renderer cache and
+        let ``original_on_resize`` recalculate layout.
+        """
         app = MagicMock()
-        out = app.renderer.output
         events = []
-        out.reset_attributes.side_effect = lambda: events.append("reset_attrs")
-        out.erase_screen.side_effect = lambda: events.append("erase")
-        out.write_raw.side_effect = lambda text: events.append(("raw", text))
-        out.cursor_goto.side_effect = lambda *_: events.append("home")
-        out.flush.side_effect = lambda: events.append("flush")
         app.renderer.reset.side_effect = lambda **_: events.append("renderer_reset")
-        monkeypatch.setattr(cli_mod, "_replay_output_history", lambda: events.append("replay"))
+        app.invalidate.side_effect = lambda: events.append("invalidate")
         original_on_resize = lambda: events.append("original_resize")
 
         bare_cli._recover_after_resize(app, original_on_resize)
 
         assert events == [
-            "reset_attrs",
-            "erase",
-            ("raw", "\x1b[3J"),
-            "home",
-            "flush",
             "renderer_reset",
-            "replay",
+            "invalidate",
             "original_resize",
         ]
-        app.invalidate.assert_not_called()
+        # Must NOT clear the screen or scrollback — those destroy the banner.
+        app.renderer.output.erase_screen.assert_not_called()
+        app.renderer.output.write_raw.assert_not_called()
+        app.renderer.output.cursor_goto.assert_not_called()
 
     def test_force_redraw_uses_full_screen_clear_without_scrollback_clear(self, bare_cli):
         app = MagicMock()