fix(tui): harden plugin slash exec errors

tests/tui_gateway/test_protocol.py

@@ -421,6 +421,69 @@ def test_slash_exec_handles_plugin_commands_in_live_gateway(server):
     assert worker.calls == []
 
 
+def test_slash_exec_plugin_lookup_failure_falls_back_to_worker(server):
+    """Plugin discovery failures must not break ordinary slash-worker commands."""
+    sid = "test-session"
+
+    class Worker:
+        def __init__(self):
+            self.calls = []
+
+        def run(self, cmd):
+            self.calls.append(cmd)
+            return f"worker:{cmd}"
+
+    worker = Worker()
+    server._sessions[sid] = {"session_key": sid, "agent": None, "slash_worker": worker}
+
+    with patch(
+        "hermes_cli.plugins.get_plugin_command_handler",
+        side_effect=RuntimeError("discovery boom"),
+    ):
+        resp = server.handle_request({
+            "id": "r-plugin-lookup-failure",
+            "method": "slash.exec",
+            "params": {"command": "help", "session_id": sid},
+        })
+
+    assert "error" not in resp
+    assert resp["result"] == {"output": "worker:help"}
+    assert worker.calls == ["help"]
+
+
+def test_slash_exec_plugin_handler_error_returns_output(server):
+    """Plugin handler failures return slash output so the TUI does not redispatch."""
+    sid = "test-session"
+
+    class Worker:
+        def __init__(self):
+            self.calls = []
+
+        def run(self, cmd):
+            self.calls.append(cmd)
+            return f"worker:{cmd}"
+
+    def handler(arg):
+        raise RuntimeError(f"handler boom: {arg}")
+
+    worker = Worker()
+    server._sessions[sid] = {"session_key": sid, "agent": None, "slash_worker": worker}
+
+    with patch(
+        "hermes_cli.plugins.get_plugin_command_handler",
+        lambda name: handler if name == "plugin-cmd" else None,
+    ):
+        resp = server.handle_request({
+            "id": "r-plugin-handler-error",
+            "method": "slash.exec",
+            "params": {"command": "plugin-cmd hello", "session_id": sid},
+        })
+
+    assert "error" not in resp
+    assert resp["result"] == {"output": "Plugin command error: handler boom: hello"}
+    assert worker.calls == []
+
+
 @pytest.mark.parametrize("cmd", ["retry", "queue hello", "q hello", "steer fix the test", "plan"])
 def test_slash_exec_rejects_pending_input_commands(server, cmd):
     """slash.exec must reject commands that use _pending_input in the CLI."""

tui_gateway/server.py

@@ -5189,19 +5189,26 @@ def _(rid, params: dict) -> dict:
     except Exception:
         pass
 
+    plugin_handler = None
+    resolve_plugin_command_result = None
+    if _cmd_base:
         try:
             from hermes_cli.plugins import (
                 get_plugin_command_handler,
                 resolve_plugin_command_result,
             )
 
-        if _cmd_base:
             plugin_handler = get_plugin_command_handler(_cmd_base)
-            if plugin_handler:
+        except Exception:
+            plugin_handler = None
+            resolve_plugin_command_result = None
+
+    if plugin_handler and resolve_plugin_command_result:
+        try:
             result = resolve_plugin_command_result(plugin_handler(_cmd_arg))
             return _ok(rid, {"output": str(result or "(no output)")})
         except Exception as e:
-        return _err(rid, 4018, f"plugin command error: {e}")
+            return _ok(rid, {"output": f"Plugin command error: {e}"})
 
     worker = session.get("slash_worker")
     if not worker: