diff --git a/lumni/src/apps/builtin/llm/prompt/src/tui/events/handle_prompt_window.rs b/lumni/src/apps/builtin/llm/prompt/src/tui/events/handle_prompt_window.rs
index 59c6ba8e..19420dc7 100644
--- a/lumni/src/apps/builtin/llm/prompt/src/tui/events/handle_prompt_window.rs
+++ b/lumni/src/apps/builtin/llm/prompt/src/tui/events/handle_prompt_window.rs
@@ -97,6 +97,14 @@ pub fn handle_prompt_window_event(
                     '-' => {
                         app_ui.set_primary_window(WindowKind::ResponseWindow);
                     }
+                    ' ' => {
+                        if let Some(prev) = key_track.previous_key_str() {
+                            if prev == " " {
+                                // change to insert mode if double space
+                                return Ok(Some(app_ui.set_prompt_window(true)));
+                            }
+                        }
+                    }
                     _ => {}
                 }
             }
diff --git a/lumni/src/apps/builtin/llm/prompt/src/tui/events/key_event.rs b/lumni/src/apps/builtin/llm/prompt/src/tui/events/key_event.rs
index d574758e..719b7b62 100644
--- a/lumni/src/apps/builtin/llm/prompt/src/tui/events/key_event.rs
+++ b/lumni/src/apps/builtin/llm/prompt/src/tui/events/key_event.rs
@@ -68,7 +68,8 @@ impl KeyTrack {
             }
             match new_c {
                 ' ' => {
-                    self.previous_key_str = Some(String::new());
+                    // double space
+                    self.set_leader_key(false);
                 }
                 'i' => {
                     // currently insert always disables leader key