feat(client): add "Open config.toml" link to the settings footer

Windows Terminal's "Open JSON file" equivalent: a right-aligned accent
link in the settings-panel footer bar opens config.toml with the OS
default editor.

- `platform::open_config_file` follows the `open_releases_url` pattern
  (open / xdg-open / `cmd /c start "" <path>` with CREATE_NO_WINDOW; the
  empty title argument keeps paths with spaces intact) and creates the
  file first when it does not exist yet.
- Hit-test mirrors the footer geometry (`bottom_y` formula) and only the
  label region is clickable; the link colour goes through
  `ensure_readable` for the 4.5:1 contrast rule.
- i18n: new `settings-open-config-file` key in all 8 locales.

Note: the per-field "restore default" item originally planned for this
phase moves into the P2 row-refactor, which introduces the per-row
metadata it needs.

Generated with [Claude Code](https://claude.ai/code)
via [Happy](https://happy.engineering)

Co-Authored-By: Claude <noreply@anthropic.com>
Co-Authored-By: Happy <yesreply@happy.engineering>

Author: 3 people

CHANGELOG.md

@@ -7,6 +7,12 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Added
+- Settings panel: an "Open config.toml" link in the footer bar opens the
+  configuration file with the OS default editor (Windows Terminal's
+  "Open JSON file" equivalent). Creates the file first when it does not
+  exist yet.
+
 ## [1.14.0] - 2026-07-12
 
 Windows console-flash fix and a Windows-Terminal-inspired settings-panel

nexterm-client-gpu/src/platform.rs

@@ -70,6 +70,41 @@ pub(crate) fn cursor_screen_pos() -> Option<(i32, i32)> {
     }
 }
 
+/// Open `config.toml` with the OS default handler (P4, WT's "Open JSON
+/// file" equivalent). Creates an empty file first when it does not exist
+/// yet, so the editor does not error out on a missing path.
+pub(crate) fn open_config_file() {
+    let path = nexterm_config::toml_path();
+    if !path.exists() {
+        if let Some(parent) = path.parent() {
+            let _ = std::fs::create_dir_all(parent);
+        }
+        if let Err(e) = std::fs::write(&path, "") {
+            tracing::warn!("failed to create {}: {}", path.display(), e);
+            return;
+        }
+    }
+    let path_str = path.to_string_lossy().to_string();
+    #[cfg(target_os = "macos")]
+    let _ = std::process::Command::new("open").arg(&path_str).spawn();
+    #[cfg(target_os = "linux")]
+    let _ = std::process::Command::new("xdg-open")
+        .arg(&path_str)
+        .spawn();
+    #[cfg(windows)]
+    {
+        use std::os::windows::process::CommandExt;
+        use windows_sys::Win32::System::Threading::CREATE_NO_WINDOW;
+        // Without CREATE_NO_WINDOW a GUI-subsystem process spawning a console
+        // app briefly flashes a black console window. `start ""` keeps paths
+        // with spaces from being consumed as the window title.
+        let _ = std::process::Command::new("cmd")
+            .args(["/c", "start", "", &path_str])
+            .creation_flags(CREATE_NO_WINDOW)
+            .spawn();
+    }
+}
+
 /// Open the GitHub releases page in the default browser.
 pub(crate) fn open_releases_url() {
     let url = "https://github.com/mizu-jun/nexterm/releases/latest";

nexterm-client-gpu/src/renderer/event_handler/mouse.rs

@@ -634,6 +634,11 @@ impl EventHandler {
                         // Click outside the panel → close the panel.
                         self.app.state.settings_panel.close();
                     }
+                    SettingsPanelHit::OpenConfigFile => {
+                        // P4 (WT-like UX): open config.toml with the OS
+                        // default editor (WT's "Open JSON file" equivalent).
+                        crate::platform::open_config_file();
+                    }
                     SettingsPanelHit::Category(idx) => {
                         // Click on a sidebar category → switch category. With
                         // a non-empty Phase 4 search, the rendered list is the

nexterm-client-gpu/src/renderer/event_handler/settings_panel_hit.rs

@@ -43,6 +43,8 @@ pub(super) enum SettingsPanelHit {
     /// cyclers (click cycles forward), 4..=6 are byte-cap fields (click focuses
     /// and starts editing). The footer note row has no hit zone.
     SecurityRow(u8),
+    /// P4 (WT-like UX): the "Open config.toml" link in the footer bar.
+    OpenConfigFile,
     /// Empty area inside the panel (no-op).
     PanelBackground,
     /// Phase 4 (UI/UX v2): click landed on the sidebar search input.
@@ -106,6 +108,21 @@ impl EventHandler {
             return SettingsPanelHit::TitleBar;
         }
 
+        // Footer bar — mirrors the `bottom_y` formula in
+        // `overlay/settings/mod.rs`. The right-aligned "Open config.toml"
+        // link is the only clickable region; the rest is a no-op. Checked
+        // before the sidebar branch because the footer spans the full panel
+        // width below the sidebar.
+        let footer_y = py + panel_h - cell_h * 1.5;
+        if cy >= footer_y {
+            let label = format!("↗ {}", nexterm_i18n::fl!("settings-open-config-file"));
+            let label_w = crate::vertex_util::visual_width(&label) as f32 * cell_w;
+            if cx >= px + panel_w - label_w - cell_w {
+                return SettingsPanelHit::OpenConfigFile;
+            }
+            return SettingsPanelHit::PanelBackground;
+        }
+
         // Sidebar — first the Phase 4 search input (reserved strip at the
         // top), then the category list below it.
         let sidebar_top = py + title_h;

nexterm-client-gpu/src/renderer/overlay/settings/mod.rs

@@ -619,6 +619,31 @@ impl WgpuState {
             text_idx,
         );
 
+        // P4 (WT-like UX): right-aligned "Open config.toml" link (WT's
+        // "Open JSON file" equivalent). The hit-test in
+        // `settings_panel_hit.rs` mirrors this exact geometry.
+        let open_label = format!("↗ {}", nexterm_i18n::fl!("settings-open-config-file"));
+        let open_label_w = crate::vertex_util::visual_width(&open_label) as f32 * cell_w;
+        add_string_verts(
+            &open_label,
+            px + panel_w - open_label_w - cell_w,
+            bottom_y + cell_h * 0.3,
+            row::ensure_readable(
+                tokens.accent_primary,
+                tokens.surface_0,
+                row::MIN_TEXT_CONTRAST,
+            ),
+            false,
+            sw,
+            sh,
+            cell_w,
+            font,
+            atlas,
+            &self.queue,
+            text_verts,
+            text_idx,
+        );
+
         // Phase B3: the open/close animation is expressed purely through
         // `slide_offset` (position) above — there used to also be a
         // translucent "fade-in" wash drawn over the entire panel here,

nexterm-i18n/locales/de.json

@@ -97,6 +97,7 @@
   "settings-category-security": "Sicherheit",
   "settings-panel-title": " * Nexterm-Einstellungen",
   "settings-panel-footer-hint": "  Enter=Speichern  Esc=Abbrechen  Tab=Nächste Kategorie",
+  "settings-open-config-file": "config.toml öffnen",
   "settings-search-placeholder-typing": "/ Zum Filtern tippen…",
   "settings-search-placeholder-idle": "/ Kategorien durchsuchen",
   "settings-startup-language": "Sprache",

nexterm-i18n/locales/en.json

@@ -97,6 +97,7 @@
   "settings-category-security": "Security",
   "settings-panel-title": " * Nexterm Settings",
   "settings-panel-footer-hint": "  Enter=Save  Esc=Cancel  Tab=Next category",
+  "settings-open-config-file": "Open config.toml",
   "settings-search-placeholder-typing": "/ Type to filter…",
   "settings-search-placeholder-idle": "/ Search categories",
   "settings-startup-language": "Language",

nexterm-i18n/locales/es.json

@@ -97,6 +97,7 @@
   "settings-category-security": "Seguridad",
   "settings-panel-title": " * Ajustes de Nexterm",
   "settings-panel-footer-hint": "  Intro=Guardar  Esc=Cancelar  Tab=Siguiente categoría",
+  "settings-open-config-file": "Abrir config.toml",
   "settings-search-placeholder-typing": "/ Escriba para filtrar…",
   "settings-search-placeholder-idle": "/ Buscar categorías",
   "settings-startup-language": "Idioma",

nexterm-i18n/locales/fr.json

@@ -97,6 +97,7 @@
   "settings-category-security": "Sécurité",
   "settings-panel-title": " * Paramètres Nexterm",
   "settings-panel-footer-hint": "  Entrée=Enregistrer  Échap=Annuler  Tab=Catégorie suivante",
+  "settings-open-config-file": "Ouvrir config.toml",
   "settings-search-placeholder-typing": "/ Tapez pour filtrer…",
   "settings-search-placeholder-idle": "/ Rechercher des catégories",
   "settings-startup-language": "Langue",

nexterm-i18n/locales/it.json

@@ -97,6 +97,7 @@
   "settings-category-security": "Sicurezza",
   "settings-panel-title": " * Impostazioni di Nexterm",
   "settings-panel-footer-hint": "  Invio=Salva  Esc=Annulla  Tab=Categoria successiva",
+  "settings-open-config-file": "Apri config.toml",
   "settings-search-placeholder-typing": "/ Digita per filtrare…",
   "settings-search-placeholder-idle": "/ Cerca categorie",
   "settings-startup-language": "Lingua",