feat: added a .fork command to fork a new session from a running conversation

src/config/request_context.rs

@@ -633,6 +633,43 @@ impl RequestContext {
         Ok(())
     }
 
+    pub fn fork_session(&mut self, fork_name: Option<&str>) -> Result<()> {
+        let current_name = match &self.session {
+            Some(s) => s.name().to_string(),
+            None => bail!("No active session to fork"),
+        };
+
+        let fork_name: String = match fork_name {
+            Some(name) => name.to_string(),
+            None => {
+                let base = fork_base_name(&current_name);
+                let sessions_dir = self.sessions_dir();
+                (1_u32..)
+                    .map(|n| format!("{base}-fork-{n}"))
+                    .find(|name| !sessions_dir.join(format!("{name}.yaml")).exists())
+                    .unwrap()
+            }
+        };
+
+        let fork_path = self.session_file(&fork_name);
+        if fork_path.exists() {
+            bail!("Session '{}' already exists", fork_name);
+        }
+
+        self.save_session(None)?;
+
+        let session = self.session.as_ref().unwrap();
+        let mut fork = session.clone();
+        fork.set_name(fork_name.clone());
+        fork.clear_autoname();
+        fork.save(&fork_name, &fork_path, self.working_mode.is_repl())?;
+
+        self.session = Some(fork);
+        println!("Forked '{current_name}' → '{fork_name}'");
+
+        Ok(())
+    }
+
     pub fn empty_session(&mut self) -> Result<()> {
         if let Some(session) = self.session.as_mut() {
             if let Some(agent) = self.agent.as_ref() {
@@ -4053,6 +4090,17 @@ impl RequestContext {
     }
 }
 
+fn fork_base_name(name: &str) -> &str {
+    if let Some(pos) = name.rfind("-fork-") {
+        let suffix = &name[pos + 6..];
+        if !suffix.is_empty() && suffix.chars().all(|c| c.is_ascii_digit()) {
+            return &name[..pos];
+        }
+    }
+
+    name
+}
+
 #[cfg(test)]
 mod tests {
     use super::super::mcp_factory::McpFactory;
@@ -5456,6 +5504,32 @@ mod tests {
         assert!(!ctx.working_mode.is_cmd());
     }
 
+    #[test]
+    fn fork_base_name_strips_fork_suffix() {
+        assert_eq!(fork_base_name("my-session-fork-1"), "my-session");
+        assert_eq!(fork_base_name("my-session-fork-42"), "my-session");
+    }
+
+    #[test]
+    fn fork_base_name_leaves_plain_names_unchanged() {
+        assert_eq!(fork_base_name("my-session"), "my-session");
+        assert_eq!(fork_base_name("research"), "research");
+    }
+
+    #[test]
+    fn fork_base_name_ignores_non_numeric_suffix() {
+        assert_eq!(fork_base_name("my-session-fork-abc"), "my-session-fork-abc");
+        assert_eq!(fork_base_name("my-session-fork-"), "my-session-fork-");
+    }
+
+    #[test]
+    fn fork_base_name_flattens_nested_forks() {
+        assert_eq!(
+            fork_base_name("my-session-fork-1-fork-2"),
+            "my-session-fork-1"
+        );
+    }
+
     #[test]
     fn session_file_returns_yaml_path() {
         let ctx = create_test_ctx();

src/config/session.rs

@@ -177,6 +177,14 @@ impl Session {
         &self.name
     }
 
+    pub fn set_name(&mut self, name: String) {
+        self.name = name;
+    }
+
+    pub fn clear_autoname(&mut self) {
+        self.autoname = None;
+    }
+
     pub fn role_name(&self) -> Option<&str> {
         self.role_name.as_deref()
     }
@@ -1046,4 +1054,13 @@ mod tests {
         session.set_autonaming(true);
         assert!(!session.need_autoname());
     }
+
+    #[test]
+    fn session_set_name_updates_name() {
+        let mut session = Session::default();
+
+        session.set_name("my-fork".to_string());
+
+        assert_eq!(session.name(), "my-fork");
+    }
 }

src/repl/mod.rs

@@ -52,7 +52,7 @@ pub const DEFAULT_CONTINUATION_PROMPT: &str = indoc! {"
     4. Continue with the next pending item now. Call tools immediately."
 };
 
-static REPL_COMMANDS: LazyLock<[ReplCommand; 57]> = LazyLock::new(|| {
+static REPL_COMMANDS: LazyLock<[ReplCommand; 58]> = LazyLock::new(|| {
     [
         ReplCommand::new(".help", "Show this help guide", AssertState::pass()),
         ReplCommand::new(".info", "Show system info", AssertState::pass()),
@@ -175,6 +175,11 @@ static REPL_COMMANDS: LazyLock<[ReplCommand; 57]> = LazyLock::new(|| {
             "Exit active session",
             AssertState::True(StateFlags::SESSION_EMPTY | StateFlags::SESSION),
         ),
+        ReplCommand::new(
+            ".fork",
+            "Fork the active session into a new named copy",
+            AssertState::True(StateFlags::SESSION),
+        ),
         ReplCommand::new(".agent", "Use an agent", AssertState::bare()),
         ReplCommand::new(
             ".starter",
@@ -1018,6 +1023,9 @@ pub async fn run_repl_command(
                     ctx.app.config.print_markdown(&banner)?;
                 }
             },
+            ".fork" => {
+                ctx.fork_session(args)?;
+            }
             ".save" => match split_first_arg(args) {
                 Some(("role", name)) => {
                     ctx.save_role(name)?;
@@ -1744,8 +1752,8 @@ mod tests {
     }
 
     #[test]
-    fn repl_commands_has_57_entries() {
-        assert_eq!(REPL_COMMANDS.len(), 57);
+    fn repl_commands_has_58_entries() {
+        assert_eq!(REPL_COMMANDS.len(), 58);
     }
 
     #[test]