feat: Adds checkpointing functionality using Git CLI commands

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

@@ -50,6 +50,15 @@ static AVAILABLE_EXPERIMENTS: &[Experiment] = &[
         description: "Enables Q to create todo lists that can be viewed and managed using /todos",
         setting_key: Setting::EnabledTodoList,
     },
+    Experiment {
+        name: "Checkpoint",
+        description: concat!(
+            "Enables workspace checkpoints to snapshot, list, expand, diff, and restore files (/checkpoint)\n",
+            "                             ",
+            "Cannot be used in tangent mode (to avoid mixing up conversation history)"
+        ),
+        setting_key: Setting::EnabledCheckpoint,
+    },
     Experiment {
         name: "Context Usage Indicator",
         description: "Shows context usage percentage in the prompt (e.g., [rust-agent] 6% >)",

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

@@ -1,4 +1,5 @@
 pub mod changelog;
+pub mod checkpoint;
 pub mod clear;
 pub mod compact;
 pub mod context;
@@ -35,6 +36,7 @@ use tangent::TangentArgs;
 use todos::TodoSubcommand;
 use tools::ToolsArgs;
 
+use crate::cli::chat::cli::checkpoint::CheckpointSubcommand;
 use crate::cli::chat::cli::subscribe::SubscribeArgs;
 use crate::cli::chat::cli::usage::UsageArgs;
 use crate::cli::chat::consts::AGENT_MIGRATION_DOC_URL;
@@ -102,6 +104,8 @@ pub enum SlashCommand {
     Persist(PersistSubcommand),
     // #[command(flatten)]
     // Root(RootSubcommand),
+    #[command(subcommand)]
+    Checkpoint(CheckpointSubcommand),
     /// View, manage, and resume to-do lists
     #[command(subcommand)]
     Todos(TodoSubcommand),
@@ -169,6 +173,7 @@ impl SlashCommand {
             //         skip_printing_tools: true,
             //     })
             // },
+            Self::Checkpoint(subcommand) => subcommand.execute(os, session).await,
             Self::Todos(subcommand) => subcommand.execute(os, session).await,
         }
     }
@@ -198,6 +203,7 @@ impl SlashCommand {
                 PersistSubcommand::Save { .. } => "save",
                 PersistSubcommand::Load { .. } => "load",
             },
+            Self::Checkpoint(_) => "checkpoint",
             Self::Todos(_) => "todos",
         }
     }

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

@@ -65,6 +65,22 @@ impl TangentArgs {
 
         match self.subcommand {
             Some(TangentSubcommand::Tail) => {
+                // Check if checkpoint is enabled
+                if os
+                    .database
+                    .settings
+                    .get_bool(Setting::EnabledCheckpoint)
+                    .unwrap_or(false)
+                {
+                    execute!(
+                        session.stderr,
+                        style::SetForegroundColor(Color::Yellow),
+                        style::Print(
+                            "⚠️ Checkpoint is disabled while in tangent mode. Please exit tangent mode if you want to use checkpoint.\n"
+                        ),
+                        style::SetForegroundColor(Color::Reset),
+                    )?;
+                }
                 if session.conversation.is_in_tangent_mode() {
                     let duration_seconds = session.conversation.get_tangent_duration_seconds().unwrap_or(0);
                     session.conversation.exit_tangent_mode_with_tail();
@@ -106,6 +122,23 @@ impl TangentArgs {
                         style::SetForegroundColor(Color::Reset)
                     )?;
                 } else {
+                    // Check if checkpoint is enabled
+                    if os
+                        .database
+                        .settings
+                        .get_bool(Setting::EnabledCheckpoint)
+                        .unwrap_or(false)
+                    {
+                        execute!(
+                            session.stderr,
+                            style::SetForegroundColor(Color::Yellow),
+                            style::Print(
+                                "⚠️ Checkpoint is disabled while in tangent mode. Please exit tangent mode if you want to use checkpoint.\n"
+                            ),
+                            style::SetForegroundColor(Color::Reset),
+                        )?;
+                    }
+
                     session.conversation.enter_tangent_mode();
 
                     // Get the configured tangent mode key for display

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

@@ -74,6 +74,10 @@ use crate::cli::agent::hook::{
     HookTrigger,
 };
 use crate::cli::chat::ChatError;
+use crate::cli::chat::checkpoint::{
+    Checkpoint,
+    CheckpointManager,
+};
 use crate::cli::chat::cli::model::{
     ModelInfo,
     get_model_info,
@@ -138,6 +142,8 @@ pub struct ConversationState {
     /// Maps from a file path to [FileLineTracker]
     #[serde(default)]
     pub file_line_tracker: HashMap<String, FileLineTracker>,
+
+    pub checkpoint_manager: Option<CheckpointManager>,
     #[serde(default = "default_true")]
     pub mcp_enabled: bool,
     /// Tangent mode checkpoint - stores main conversation when in tangent mode
@@ -203,6 +209,7 @@ impl ConversationState {
             model: None,
             model_info: model,
             file_line_tracker: HashMap::new(),
+            checkpoint_manager: None,
             mcp_enabled,
             tangent_state: None,
         }
@@ -891,6 +898,20 @@ Return only the JSON configuration, no additional text.",
         self.transcript.push_back(message);
     }
 
+    /// Restore conversation from a checkpoint's history snapshot
+    pub fn restore_to_checkpoint(&mut self, checkpoint: &Checkpoint) -> Result<(), eyre::Report> {
+        // 1. Restore history from snapshot
+        self.history = checkpoint.history_snapshot.clone();
+
+        // 2. Clear any pending next message (uncommitted state)
+        self.next_message = None;
+
+        // 3. Update valid history range
+        self.valid_history_range = (0, self.history.len());
+
+        Ok(())
+    }
+
     /// Swapping agent involves the following:
     /// - Reinstantiate the context manager
     /// - Swap agent on tool manager