feat: add auto-save functionality for chat conversations

- Add chat.enableAutoSave and chat.autoSavePath settings
- Implement AutoSaveManager for session-based auto-saving
- Auto-save triggers after AI response completion
- Silent error handling to avoid interrupting conversations
- Opt-in by default (disabled)

Closes #3322

Author: NB3025

crates/chat-cli/src/cli/chat/auto_save.rs

@@ -0,0 +1,61 @@
+use crate::database::settings::Setting;
+use crate::os::Os;
+use crate::cli::chat::conversation::ConversationState;
+use chrono::Local;
+use tracing::warn;
+
+pub struct AutoSaveManager {
+    session_filename: Option<String>,
+}
+
+impl AutoSaveManager {
+    pub fn new() -> Self {
+        Self {
+            session_filename: None,
+        }
+    }
+
+    pub async fn auto_save_if_enabled(
+        &mut self,
+        os: &Os,
+        conversation: &ConversationState,
+    ) -> Result<(), Box<dyn std::error::Error>> {
+        // Check if auto-save is enabled
+        let auto_save_enabled = os.database.settings.get_bool(Setting::ChatEnableAutoSave).unwrap_or(false);
+        tracing::info!("Auto-save check: enabled={}", auto_save_enabled);
+        
+        if !auto_save_enabled {
+            return Ok(());
+        }
+
+        // Generate filename on first save
+        if self.session_filename.is_none() {
+            let pattern = os.database.settings
+                .get_string(Setting::ChatAutoSavePath)
+                .unwrap_or_else(|| "auto-save-{timestamp}.json".to_string());
+            
+            let timestamp = Local::now().format("%Y%m%d-%H%M%S");
+            let filename = pattern.replace("{timestamp}", &timestamp.to_string());
+            tracing::info!("Auto-save: generating filename: {}", filename);
+            self.session_filename = Some(filename);
+        }
+
+        // Execute auto-save
+        if let Some(filename) = &self.session_filename {
+            tracing::info!("Auto-save: attempting to save to {}", filename);
+            match serde_json::to_string_pretty(conversation) {
+                Ok(contents) => {
+                    match os.fs.write(filename, contents).await {
+                        Ok(_) => tracing::info!("Auto-save: successfully saved to {}", filename),
+                        Err(e) => warn!("Auto-save failed: {}", e),
+                    }
+                }
+                Err(e) => {
+                    warn!("Auto-save serialization failed: {}", e);
+                }
+            }
+        }
+
+        Ok(())
+    }
+}

crates/chat-cli/src/cli/chat/mod.rs

@@ -12,6 +12,7 @@ pub mod cli;
 mod consts;
 pub mod context;
 mod conversation;
+mod auto_save;
 mod input_source;
 mod message;
 mod parse;
@@ -677,6 +678,7 @@ pub struct ChatSession {
     prompt_ack_rx: std::sync::mpsc::Receiver<()>,
     /// Additional context to be added to the next user message (e.g., delegate task summaries)
     pending_additional_context: Option<String>,
+    auto_save_manager: auto_save::AutoSaveManager,
 }
 
 impl ChatSession {
@@ -814,6 +816,7 @@ impl ChatSession {
             wrap,
             prompt_ack_rx,
             pending_additional_context: None,
+            auto_save_manager: auto_save::AutoSaveManager::new(),
         })
     }
 
@@ -1172,6 +1175,11 @@ impl ChatSession {
         self.tool_turn_start_time = None;
         self.reset_user_turn();
 
+        // Auto-save conversation if enabled
+        if let Err(e) = self.auto_save_manager.auto_save_if_enabled(os, &self.conversation).await {
+            warn!("Auto-save error: {}", e);
+        }
+
         self.inner = Some(ChatState::PromptUser {
             skip_printing_tools: false,
         });
@@ -3207,6 +3215,11 @@ impl ChatSession {
                     .await;
             }
 
+            // Auto-save conversation if enabled
+            if let Err(e) = self.auto_save_manager.auto_save_if_enabled(os, &self.conversation).await {
+                warn!("Auto-save error: {}", e);
+            }
+
             Ok(ChatState::PromptUser {
                 skip_printing_tools: false,
             })

crates/chat-cli/src/database/settings.rs

@@ -89,6 +89,10 @@ pub enum Setting {
     EnabledCheckpoint,
     #[strum(message = "Enable the delegate tool for subagent management (boolean)")]
     EnabledDelegate,
+    #[strum(message = "Enable automatic conversation saving (boolean)")]
+    ChatEnableAutoSave,
+    #[strum(message = "Auto-save file path pattern (string)")]
+    ChatAutoSavePath,
     #[strum(message = "Specify UI variant to use (string)")]
     UiMode,
 }
@@ -132,6 +136,8 @@ impl AsRef<str> for Setting {
             Self::EnabledCheckpoint => "chat.enableCheckpoint",
             Self::EnabledContextUsageIndicator => "chat.enableContextUsageIndicator",
             Self::EnabledDelegate => "chat.enableDelegate",
+            Self::ChatEnableAutoSave => "chat.enableAutoSave",
+            Self::ChatAutoSavePath => "chat.autoSavePath",
             Self::UiMode => "chat.uiMode",
         }
     }
@@ -182,6 +188,9 @@ impl TryFrom<&str> for Setting {
             "chat.enableTodoList" => Ok(Self::EnabledTodoList),
             "chat.enableCheckpoint" => Ok(Self::EnabledCheckpoint),
             "chat.enableContextUsageIndicator" => Ok(Self::EnabledContextUsageIndicator),
+            "chat.enableDelegate" => Ok(Self::EnabledDelegate),
+            "chat.enableAutoSave" => Ok(Self::ChatEnableAutoSave),
+            "chat.autoSavePath" => Ok(Self::ChatAutoSavePath),
             "chat.uiMode" => Ok(Self::UiMode),
             _ => Err(DatabaseError::InvalidSetting(value.to_string())),
         }