diff --git a/tests/test_tui_gateway_server.py b/tests/test_tui_gateway_server.py
index 107d238977..0db89cecab 100644
--- a/tests/test_tui_gateway_server.py
+++ b/tests/test_tui_gateway_server.py
@@ -730,6 +730,41 @@ def test_complete_slash_surfaces_completer_error(monkeypatch):
     assert "no completer" in resp["error"]["message"]
 
 
+def test_complete_slash_display_is_plain_string(monkeypatch):
+    """complete.slash must convert prompt_toolkit FormattedText display values
+    to plain strings before sending them over RPC.
+
+    Regression: c.display is a FormattedText object, not a str.  Passing it
+    raw caused JSON serialization failures and broken rendering in the TUI
+    completion dropdown.
+    """
+    from prompt_toolkit.formatted_text import FormattedText
+
+    class _FakeCompletion:
+        text = "/resume"
+        display = FormattedText([("class:command", "/resume")])
+        display_meta = FormattedText([("", "Resume a session")])
+
+    with patch("hermes_cli.commands.SlashCommandCompleter") as MockCompleter:
+        instance = MockCompleter.return_value
+        instance.get_completions.return_value = [_FakeCompletion()]
+
+        resp = server.handle_request(
+            {"id": "1", "method": "complete.slash", "params": {"text": "/res"}}
+        )
+
+    assert "result" in resp, resp
+    items = resp["result"]["items"]
+    assert len(items) >= 1
+    item = next(i for i in items if i["text"] == "/resume")
+    assert isinstance(item["display"], str), (
+        "display must be a plain str — FormattedText breaks JSON serialization"
+    )
+    assert item["display"] == "/resume"
+    assert isinstance(item["meta"], str)
+    assert item["meta"] == "Resume a session"
+
+
 def test_input_detect_drop_attaches_image(monkeypatch):
     fake_cli = types.ModuleType("cli")
     fake_cli._detect_file_drop = lambda raw: {
diff --git a/tui_gateway/server.py b/tui_gateway/server.py
index 7bc0fb2e09..9f6b92ce93 100644
--- a/tui_gateway/server.py
+++ b/tui_gateway/server.py
@@ -3650,7 +3650,7 @@ def _(rid, params: dict) -> dict:
         items = [
             {
                 "text": c.text,
-                "display": c.display or c.text,
+                "display": to_plain_text(c.display) if c.display else c.text,
                 "meta": to_plain_text(c.display_meta) if c.display_meta else "",
             }
             for c in completer.get_completions(doc, None)
diff --git a/ui-tui/src/components/appLayout.tsx b/ui-tui/src/components/appLayout.tsx
index d856451751..9ed819b6d6 100644
--- a/ui-tui/src/components/appLayout.tsx
+++ b/ui-tui/src/components/appLayout.tsx
@@ -203,7 +203,7 @@ const ComposerPane = memo(function ComposerPane({
         <FloatingOverlays
           cols={composer.cols}
           compIdx={composer.compIdx}
-          completions={composer.completions}
+          completions={isBlocked ? [] : composer.completions}
           onModelSelect={actions.onModelSelect}
           onPickerSelect={actions.resumeById}
           pagerPageSize={composer.pagerPageSize}