Improve the default system prompt

src/app.rs

@@ -185,7 +185,7 @@ pub(crate) enum Message {
     PreferenceEndpointCorsChanged(bool),
     PreferenceContextChanged(String),
     PreferenceMaxTokensChanged(String),
-    PreferenceSystemPromptChanged(String),
+    PreferenceSystemPromptAction(text_editor::Action),
     PreferenceTemperatureChanged(String),
     PreferenceTopPChanged(String),
     PreferenceMinPChanged(String),
@@ -684,8 +684,8 @@ impl App {
                 self.preference_draft.max_generated_tokens = value;
                 self.preference_error = None;
             }
-            Message::PreferenceSystemPromptChanged(value) => {
-                self.preference_draft.system_prompt = value;
+            Message::PreferenceSystemPromptAction(action) => {
+                self.preference_draft.system_prompt.perform(action);
                 self.preference_error = None;
             }
             Message::PreferenceTemperatureChanged(value) => {

src/app/preferences.rs

@@ -12,7 +12,7 @@ pub(super) struct PreferenceDraft {
     pub(super) endpoint_cors: bool,
     pub(super) context_tokens: String,
     pub(super) max_generated_tokens: String,
-    pub(super) system_prompt: String,
+    pub(super) system_prompt: text_editor::Content,
     pub(super) temperature: String,
     pub(super) top_p: String,
     pub(super) min_p: String,
@@ -62,7 +62,7 @@ impl PreferenceDraft {
             endpoint_cors: config.endpoint.cors,
             context_tokens: generation.context_tokens.to_string(),
             max_generated_tokens: generation.max_generated_tokens.to_string(),
-            system_prompt: generation.system_prompt.clone(),
+            system_prompt: text_editor::Content::with_text(&generation.system_prompt),
             temperature: optional_string(generation.temperature),
             top_p: optional_string(generation.top_p),
             min_p: optional_string(generation.min_p),
@@ -111,7 +111,7 @@ impl PreferenceDraft {
                 "Maximum generated tokens",
                 &self.max_generated_tokens,
             )?,
-            system_prompt: self.system_prompt.clone(),
+            system_prompt: self.system_prompt.text(),
             temperature: parse_optional_f32("Temperature", &self.temperature)?,
             top_p: parse_optional_f32("Top-p", &self.top_p)?,
             min_p: parse_optional_f32("Min-p", &self.min_p)?,
@@ -423,6 +423,16 @@ impl App {
 mod tests {
     use super::*;
 
+    #[test]
+    fn multiline_system_prompt_round_trips_through_the_editor() {
+        let draft = PreferenceDraft::from_saved(&Config::default());
+
+        assert_eq!(
+            draft.generation().unwrap().system_prompt,
+            crate::settings::DEFAULT_SYSTEM_PROMPT
+        );
+    }
+
     #[test]
     fn runtime_config_updates_after_lock_poisoning() {
         let runtime = Arc::new(RwLock::new(Config::default()));

src/app/view.rs

@@ -18,8 +18,8 @@ use crate::settings::{GIB, REASONING_MODES};
 use iced::theme::{Palette, palette};
 use iced::widget::{
     Button, Space, Svg, Tooltip, button, checkbox, column, container, image, markdown, mouse_area,
-    opaque, pick_list, progress_bar, row, rule, scrollable, slider, stack, svg, text, text_input,
-    tooltip,
+    opaque, pick_list, progress_bar, row, rule, scrollable, slider, stack, svg, text, text_editor,
+    text_input, tooltip,
 };
 use iced::{Alignment, Background, Border, Color, Element, Length, Padding, Theme, window};
 use std::collections::VecDeque;

src/app/view/preferences.rs

@@ -173,12 +173,11 @@ impl App {
                     text("System prompt").size(13),
                     "Standing instruction sent before every conversation: persona, tone, house rules. Leave it empty to send no system message at all.",
                 ),
-                text_input(
-                    "You are a helpful assistant",
-                    &self.preference_draft.system_prompt,
-                )
-                .on_input(Message::PreferenceSystemPromptChanged)
-                .padding(9),
+                text_editor(&self.preference_draft.system_prompt)
+                    .placeholder("Additional system instructions…")
+                    .height(140)
+                    .on_action(Message::PreferenceSystemPromptAction)
+                    .padding(9),
                 Space::new().height(4),
                 text("SAMPLING & REASONING").size(11).color(muted_text()),
                 preference_input_row(

src/settings.rs

@@ -537,12 +537,14 @@ pub(crate) struct GenerationPreferences {
     pub(crate) reasoning_mode: ReasoningMode,
 }
 
+pub(crate) const DEFAULT_SYSTEM_PROMPT: &str = "You are an expert coding assistant operating inside DS4Server, a local coding agent harness. You help users by reading files, executing commands, editing code, and writing new files.\n\nGuidelines:\n- Be concise in your responses\n- Show file paths clearly when working with files";
+
 impl Default for GenerationPreferences {
     fn default() -> Self {
         Self {
             context_tokens: 32_768,
             max_generated_tokens: 50_000,
-            system_prompt: "You are a helpful assistant".into(),
+            system_prompt: DEFAULT_SYSTEM_PROMPT.into(),
             temperature: None,
             top_p: None,
             min_p: None,
@@ -667,6 +669,8 @@ mod tests {
     #[test]
     fn effective_settings_preserve_unset_model_defaults() {
         let defaults = GenerationPreferences::default();
+        assert_eq!(defaults.system_prompt, DEFAULT_SYSTEM_PROMPT);
+        assert!(defaults.system_prompt.contains("\n\nGuidelines:\n-"));
         let cache = KvCachePreferences::default().settings();
         let deepseek = defaults.turn_settings(ModelChoice::DeepSeekV4Flash, cache);
         assert_eq!(