feat(iced): add filter instant preview

hcie-iced-app/crates/hcie-iced-gui/src/app.rs

@@ -350,6 +350,9 @@ pub enum Message {
     FilterApply,
     FilterReset,
     FilterParamChanged(String, serde_json::Value),
+    FilterPreviewToggle(bool),
+    FilterPreviewApply,
+    FilterPreviewRestore,
 
     // ── Dialogs ─────────────────────────────────────────
     DialogOpen(ActiveDialog),
@@ -1768,6 +1771,46 @@ impl HcieIcedApp {
                 self.filter_params = serde_json::json!({});
             }
 
+            Message::FilterPreviewToggle(enabled) => {
+                self.filter_preview_active = enabled;
+                if enabled {
+                    // Start a new preview snapshot so restore can undo it
+                    self.documents[self.active_doc].engine.filter_preview_begin();
+                    // Apply the current filter with current params to show live preview
+                    if let Some(filter) = self.selected_filter {
+                        let filter_id = filter_type_to_id(filter);
+                        self.documents[self.active_doc].engine.apply_filter_preview(filter_id, self.filter_params.clone());
+                        self.refresh_composite_if_needed();
+                        return Task::perform(async {}, |_| Message::CompositeRefresh);
+                    }
+                } else {
+                    // Restore original pixels
+                    self.documents[self.active_doc].engine.filter_preview_restore();
+                    self.refresh_composite_if_needed();
+                    return Task::perform(async {}, |_| Message::CompositeRefresh);
+                }
+            }
+
+            Message::FilterPreviewApply => {
+                if let Some(filter) = self.selected_filter {
+                    let filter_id = filter_type_to_id(filter);
+                    self.documents[self.active_doc].engine.apply_filter(filter_id, self.filter_params.clone());
+                    self.refresh_composite_if_needed();
+                    self.filter_preview_active = false;
+                    self.selected_filter = None;
+                    self.filter_params = serde_json::json!({});
+                    return Task::perform(async {}, |_| Message::CompositeRefresh);
+                }
+            }
+
+            Message::FilterPreviewRestore => {
+                if self.filter_preview_active {
+                    self.documents[self.active_doc].engine.filter_preview_restore();
+                    self.refresh_composite_if_needed();
+                    return Task::perform(async {}, |_| Message::CompositeRefresh);
+                }
+            }
+
             // ── Dialogs ───────────────────────────────────
             Message::DialogOpen(dialog) => {
                 self.active_dialog = dialog;

hcie-iced-app/crates/hcie-iced-gui/src/dock/view.rs

@@ -66,7 +66,7 @@ pub fn dock_view<'a>(
                 )
             }
             PaneType::Filters => {
-                crate::panels::filters::view(app.selected_filter, &app.filter_params, colors)
+                crate::panels::filters::view(app.selected_filter, &app.filter_params, app.filter_preview_active, colors)
             }
             PaneType::ColorPicker => {
                 crate::color_picker::view(&app.fg_color, &app.bg_color, &app.recent_colors, app.color_tab)

hcie-iced-app/crates/hcie-iced-gui/src/panels/filters.rs

@@ -5,7 +5,7 @@ use crate::app::Message;
 use crate::panels::styles;
 use crate::theme::ThemeColors;
 use hcie_engine_api::FilterType;
-use iced::widget::{button, column, container, horizontal_rule, row, scrollable, text};
+use iced::widget::{button, checkbox, column, container, horizontal_rule, row, scrollable, text};
 use iced::{Element, Length};
 
 /// Filter category with its filters.
@@ -88,11 +88,12 @@ const FILTER_CATEGORIES: &[FilterCategory] = &[
 /// Build the filters panel.
 ///
 /// Shows the filter category list on top, and when a filter is selected,
-/// displays its parameter editing panel below the list. The Apply/Reset
-/// buttons are always at the bottom.
+/// displays its parameter editing panel below the list. The preview checkbox,
+/// Apply, and Reset buttons are always at the bottom.
 pub fn view(
     selected_filter: Option<FilterType>,
     filter_params: &serde_json::Value,
+    filter_preview_active: bool,
     colors: ThemeColors,
 ) -> Element<'static, Message> {
     let mut filter_list = column![].spacing(2);
@@ -145,7 +146,11 @@ pub fn view(
         .on_press(Message::FilterReset)
         .padding([6, 12]);
 
-    let buttons = row![apply_btn, reset_btn].spacing(8);
+    let preview_check = checkbox("Preview", filter_preview_active)
+        .on_toggle(Message::FilterPreviewToggle)
+        .size(11);
+
+    let buttons = row![preview_check, apply_btn, reset_btn].spacing(8);
 
     // When a filter is selected, show its parameter panel below the list.
     let param_section = match selected_filter {