diff --git a/crates/goose-server/src/openapi.rs b/crates/goose-server/src/openapi.rs
index 0e9265a6521c..c2012ef4a8bc 100644
--- a/crates/goose-server/src/openapi.rs
+++ b/crates/goose-server/src/openapi.rs
@@ -445,6 +445,7 @@ impl<'__s> ToSchema<'__s> for AnnotatedSchema {
         ModelInfo,
         SessionInfo,
         SessionMetadata,
+        goose::session::ExtensionData,
         super::routes::schedule::CreateScheduleRequest,
         super::routes::schedule::UpdateScheduleRequest,
         super::routes::schedule::KillJobResponse,
diff --git a/crates/goose/src/agents/agent.rs b/crates/goose/src/agents/agent.rs
index e78d645a680c..0503641f24e4 100644
--- a/crates/goose/src/agents/agent.rs
+++ b/crates/goose/src/agents/agent.rs
@@ -41,6 +41,7 @@ use crate::providers::errors::ProviderError;
 use crate::recipe::{Author, Recipe, Response, Settings, SubRecipe};
 use crate::scheduler_trait::SchedulerTrait;
 use crate::session;
+use crate::session::extension_data::ExtensionState;
 use crate::tool_monitor::{ToolCall, ToolMonitor};
 use crate::utils::is_token_cancelled;
 use mcp_core::ToolResult;
@@ -494,7 +495,10 @@ impl Agent {
             let todo_content = if let Some(path) = session_file_path {
                 session::storage::read_metadata(&path)
                     .ok()
-                    .and_then(|m| m.todo_content)
+                    .and_then(|m| {
+                        session::TodoState::from_extension_data(&m.extension_data)
+                            .map(|state| state.content)
+                    })
                     .unwrap_or_default()
             } else {
                 String::new()
@@ -531,7 +535,11 @@ impl Agent {
                 match session::storage::get_path(session_config.id.clone()) {
                     Ok(path) => match session::storage::read_metadata(&path) {
                         Ok(mut metadata) => {
-                            metadata.todo_content = Some(content);
+                            let todo_state = session::TodoState::new(content);
+                            todo_state
+                                .to_extension_data(&mut metadata.extension_data)
+                                .ok();
+
                             let path_clone = path.clone();
                             let metadata_clone = metadata.clone();
                             let update_result = tokio::task::spawn(async move {
diff --git a/crates/goose/src/context_mgmt/auto_compact.rs b/crates/goose/src/context_mgmt/auto_compact.rs
index 42e98240de6a..b5dbf46fc516 100644
--- a/crates/goose/src/context_mgmt/auto_compact.rs
+++ b/crates/goose/src/context_mgmt/auto_compact.rs
@@ -269,7 +269,7 @@ mod tests {
             accumulated_total_tokens: Some(100),
             accumulated_input_tokens: Some(50),
             accumulated_output_tokens: Some(50),
-            todo_content: None,
+            extension_data: crate::session::ExtensionData::new(),
         }
     }
 
diff --git a/crates/goose/src/scheduler.rs b/crates/goose/src/scheduler.rs
index bb0da404591a..c256f684ed0b 100644
--- a/crates/goose/src/scheduler.rs
+++ b/crates/goose/src/scheduler.rs
@@ -1298,7 +1298,7 @@ async fn run_scheduled_job_internal(
                             accumulated_total_tokens: None,
                             accumulated_input_tokens: None,
                             accumulated_output_tokens: None,
-                            todo_content: None,
+                            extension_data: crate::session::ExtensionData::new(),
                         };
                         if let Err(e_fb) = crate::session::storage::save_messages_with_metadata(
                             &session_file_path,
diff --git a/crates/goose/src/session/extension_data.rs b/crates/goose/src/session/extension_data.rs
new file mode 100644
index 000000000000..292415f25d38
--- /dev/null
+++ b/crates/goose/src/session/extension_data.rs
@@ -0,0 +1,173 @@
+// Extension data management for sessions
+// Provides a simple way to store extension-specific data with versioned keys
+
+use anyhow::Result;
+use serde::{Deserialize, Serialize};
+use serde_json::Value;
+use std::collections::HashMap;
+use utoipa::ToSchema;
+
+/// Extension data containing all extension states
+/// Keys are in format "extension_name.version" (e.g., "todo.v0")
+#[derive(Debug, Clone, Serialize, Deserialize, Default, ToSchema)]
+pub struct ExtensionData {
+    #[serde(flatten)]
+    pub extension_states: HashMap<String, Value>,
+}
+
+impl ExtensionData {
+    /// Create a new empty ExtensionData
+    pub fn new() -> Self {
+        Self {
+            extension_states: HashMap::new(),
+        }
+    }
+
+    /// Get extension state for a specific extension and version
+    pub fn get_extension_state(&self, extension_name: &str, version: &str) -> Option<&Value> {
+        let key = format!("{}.{}", extension_name, version);
+        self.extension_states.get(&key)
+    }
+
+    /// Set extension state for a specific extension and version
+    pub fn set_extension_state(&mut self, extension_name: &str, version: &str, state: Value) {
+        let key = format!("{}.{}", extension_name, version);
+        self.extension_states.insert(key, state);
+    }
+}
+
+/// Helper trait for extension-specific state management
+pub trait ExtensionState: Sized + Serialize + for<'de> Deserialize<'de> {
+    /// The name of the extension
+    const EXTENSION_NAME: &'static str;
+
+    /// The version of the extension state format
+    const VERSION: &'static str;
+
+    /// Convert from JSON value
+    fn from_value(value: &Value) -> Result<Self> {
+        serde_json::from_value(value.clone()).map_err(|e| {
+            anyhow::anyhow!(
+                "Failed to deserialize {} state: {}",
+                Self::EXTENSION_NAME,
+                e
+            )
+        })
+    }
+
+    /// Convert to JSON value
+    fn to_value(&self) -> Result<Value> {
+        serde_json::to_value(self).map_err(|e| {
+            anyhow::anyhow!("Failed to serialize {} state: {}", Self::EXTENSION_NAME, e)
+        })
+    }
+
+    /// Get state from extension data
+    fn from_extension_data(extension_data: &ExtensionData) -> Option<Self> {
+        extension_data
+            .get_extension_state(Self::EXTENSION_NAME, Self::VERSION)
+            .and_then(|v| Self::from_value(v).ok())
+    }
+
+    /// Save state to extension data
+    fn to_extension_data(&self, extension_data: &mut ExtensionData) -> Result<()> {
+        let value = self.to_value()?;
+        extension_data.set_extension_state(Self::EXTENSION_NAME, Self::VERSION, value);
+        Ok(())
+    }
+}
+
+/// TODO extension state implementation
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct TodoState {
+    pub content: String,
+}
+
+impl ExtensionState for TodoState {
+    const EXTENSION_NAME: &'static str = "todo";
+    const VERSION: &'static str = "v0";
+}
+
+impl TodoState {
+    /// Create a new TODO state
+    pub fn new(content: String) -> Self {
+        Self { content }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use serde_json::json;
+
+    #[test]
+    fn test_extension_data_basic_operations() {
+        let mut extension_data = ExtensionData::new();
+
+        // Test setting and getting extension state
+        let todo_state = json!({"content": "- Task 1\n- Task 2"});
+        extension_data.set_extension_state("todo", "v0", todo_state.clone());
+
+        assert_eq!(
+            extension_data.get_extension_state("todo", "v0"),
+            Some(&todo_state)
+        );
+        assert_eq!(extension_data.get_extension_state("todo", "v1"), None);
+    }
+
+    #[test]
+    fn test_multiple_extension_states() {
+        let mut extension_data = ExtensionData::new();
+
+        // Add multiple extension states
+        extension_data.set_extension_state("todo", "v0", json!("TODO content"));
+        extension_data.set_extension_state("memory", "v1", json!({"items": ["item1", "item2"]}));
+        extension_data.set_extension_state("config", "v2", json!({"setting": true}));
+
+        // Check all states exist
+        assert_eq!(extension_data.extension_states.len(), 3);
+        assert!(extension_data.get_extension_state("todo", "v0").is_some());
+        assert!(extension_data.get_extension_state("memory", "v1").is_some());
+        assert!(extension_data.get_extension_state("config", "v2").is_some());
+    }
+
+    #[test]
+    fn test_todo_state_trait() {
+        let mut extension_data = ExtensionData::new();
+
+        // Create and save TODO state
+        let todo = TodoState::new("- Task 1\n- Task 2".to_string());
+        todo.to_extension_data(&mut extension_data).unwrap();
+
+        // Retrieve TODO state
+        let retrieved = TodoState::from_extension_data(&extension_data);
+        assert!(retrieved.is_some());
+        assert_eq!(retrieved.unwrap().content, "- Task 1\n- Task 2");
+    }
+
+    #[test]
+    fn test_extension_data_serialization() {
+        let mut extension_data = ExtensionData::new();
+        extension_data.set_extension_state("todo", "v0", json!("TODO content"));
+        extension_data.set_extension_state("memory", "v1", json!({"key": "value"}));
+
+        // Serialize to JSON
+        let json = serde_json::to_value(&extension_data).unwrap();
+
+        // Check the structure
+        assert!(json.is_object());
+        assert_eq!(json.get("todo.v0"), Some(&json!("TODO content")));
+        assert_eq!(json.get("memory.v1"), Some(&json!({"key": "value"})));
+
+        // Deserialize back
+        let deserialized: ExtensionData = serde_json::from_value(json).unwrap();
+        assert_eq!(
+            deserialized.get_extension_state("todo", "v0"),
+            Some(&json!("TODO content"))
+        );
+        assert_eq!(
+            deserialized.get_extension_state("memory", "v1"),
+            Some(&json!({"key": "value"}))
+        );
+    }
+}
diff --git a/crates/goose/src/session/mod.rs b/crates/goose/src/session/mod.rs
index 5f4537fe7e6a..97381c7e522f 100644
--- a/crates/goose/src/session/mod.rs
+++ b/crates/goose/src/session/mod.rs
@@ -1,3 +1,4 @@
+pub mod extension_data;
 pub mod info;
 pub mod storage;
 
@@ -9,4 +10,5 @@ pub use storage::{
     SessionMetadata,
 };
 
+pub use extension_data::{ExtensionData, ExtensionState, TodoState};
 pub use info::{get_valid_sorted_sessions, SessionInfo};
diff --git a/crates/goose/src/session/storage.rs b/crates/goose/src/session/storage.rs
index 2da5b1112318..e8365ce87da1 100644
--- a/crates/goose/src/session/storage.rs
+++ b/crates/goose/src/session/storage.rs
@@ -8,6 +8,7 @@
 use crate::conversation::message::Message;
 use crate::conversation::Conversation;
 use crate::providers::base::Provider;
+use crate::session::extension_data::ExtensionData;
 use crate::utils::safe_truncate;
 use anyhow::Result;
 use chrono::Local;
@@ -64,11 +65,13 @@ pub struct SessionMetadata {
     pub accumulated_input_tokens: Option<i32>,
     /// The number of output tokens used in the session. Accumulated across all messages.
     pub accumulated_output_tokens: Option<i32>,
-    /// Session-scoped TODO list content
-    pub todo_content: Option<String>,
+
+    /// Extension data containing extension states
+    #[serde(default)]
+    pub extension_data: ExtensionData,
 }
 
-// Custom deserializer to handle old sessions without working_dir and todo_content
+// Custom deserializer to handle old sessions without working_dir
 impl<'de> Deserialize<'de> for SessionMetadata {
     fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
     where
@@ -78,7 +81,7 @@ impl<'de> Deserialize<'de> for SessionMetadata {
         struct Helper {
             description: String,
             message_count: usize,
-            schedule_id: Option<String>, // For backward compatibility
+            schedule_id: Option<String>,
             total_tokens: Option<i32>,
             input_tokens: Option<i32>,
             output_tokens: Option<i32>,
@@ -86,7 +89,8 @@ impl<'de> Deserialize<'de> for SessionMetadata {
             accumulated_input_tokens: Option<i32>,
             accumulated_output_tokens: Option<i32>,
             working_dir: Option<PathBuf>,
-            todo_content: Option<String>, // For backward compatibility
+            #[serde(default)]
+            extension_data: ExtensionData,
         }
 
         let helper = Helper::deserialize(deserializer)?;
@@ -108,7 +112,7 @@ impl<'de> Deserialize<'de> for SessionMetadata {
             accumulated_input_tokens: helper.accumulated_input_tokens,
             accumulated_output_tokens: helper.accumulated_output_tokens,
             working_dir,
-            todo_content: helper.todo_content,
+            extension_data: helper.extension_data,
         })
     }
 }
@@ -133,7 +137,7 @@ impl SessionMetadata {
             accumulated_total_tokens: None,
             accumulated_input_tokens: None,
             accumulated_output_tokens: None,
-            todo_content: None,
+            extension_data: ExtensionData::new(),
         }
     }
 }
diff --git a/crates/goose/tests/test_support.rs b/crates/goose/tests/test_support.rs
index eeaca03253b4..8fc851c35473 100644
--- a/crates/goose/tests/test_support.rs
+++ b/crates/goose/tests/test_support.rs
@@ -411,6 +411,6 @@ pub fn create_test_session_metadata(message_count: usize, working_dir: &str) ->
         accumulated_total_tokens: Some(100),
         accumulated_input_tokens: Some(50),
         accumulated_output_tokens: Some(50),
-        todo_content: None,
+        extension_data: Default::default(),
     }
 }
diff --git a/crates/goose/tests/todo_session_integration.rs b/crates/goose/tests/todo_session_integration.rs
index 3a58374cc6fa..dcc0402cea0d 100644
--- a/crates/goose/tests/todo_session_integration.rs
+++ b/crates/goose/tests/todo_session_integration.rs
@@ -160,7 +160,10 @@ async fn test_todo_add_persists_to_session() {
 
     // Since we're using a mock provider, we can't test the actual TODO content
     // but we can verify the metadata structure is correct
-    assert!(metadata.todo_content.is_some() || metadata.todo_content.is_none());
+    assert!(
+        metadata.extension_data.extension_states.is_empty()
+            || !metadata.extension_data.extension_states.is_empty()
+    );
 }
 
 #[tokio::test]
@@ -172,7 +175,11 @@ async fn test_todo_list_reads_from_session() {
     // Pre-populate session with TODO content
     let session_path = goose::session::storage::get_path(session_id.clone()).unwrap();
     let mut metadata = SessionMetadata::default();
-    metadata.todo_content = Some("- Task 1\n- Task 2\n- Task 3".to_string());
+    use goose::session::extension_data::{ExtensionState, TodoState};
+    let todo_state = TodoState::new("- Task 1\n- Task 2\n- Task 3".to_string());
+    todo_state
+        .to_extension_data(&mut metadata.extension_data)
+        .unwrap();
     goose::session::storage::update_metadata(&session_path, &metadata)
         .await
         .unwrap();
@@ -206,21 +213,27 @@ async fn test_todo_list_reads_from_session() {
 
     // Verify the TODO content is still in session
     let metadata_after = goose::session::storage::read_metadata(&session_path).unwrap();
+    let todo_state_after = TodoState::from_extension_data(&metadata_after.extension_data);
+    assert!(todo_state_after.is_some());
     assert_eq!(
-        metadata_after.todo_content,
-        Some("- Task 1\n- Task 2\n- Task 3".to_string())
+        todo_state_after.unwrap().content,
+        "- Task 1\n- Task 2\n- Task 3".to_string()
     );
 }
 
 #[tokio::test]
 async fn test_todo_isolation_between_sessions() {
+    use goose::session::extension_data::{ExtensionState, TodoState};
     let session1_id = session::Identifier::Name(format!("test_session_{}", Uuid::new_v4()));
     let session2_id = session::Identifier::Name(format!("test_session_{}", Uuid::new_v4()));
 
     // Add TODO to session1
     let session1_path = goose::session::storage::get_path(session1_id.clone()).unwrap();
     let mut metadata1 = SessionMetadata::default();
-    metadata1.todo_content = Some("Session 1 tasks".to_string());
+    let todo_state1 = TodoState::new("Session 1 tasks".to_string());
+    todo_state1
+        .to_extension_data(&mut metadata1.extension_data)
+        .unwrap();
     goose::session::storage::update_metadata(&session1_path, &metadata1)
         .await
         .unwrap();
@@ -228,7 +241,10 @@ async fn test_todo_isolation_between_sessions() {
     // Add different TODO to session2
     let session2_path = goose::session::storage::get_path(session2_id.clone()).unwrap();
     let mut metadata2 = SessionMetadata::default();
-    metadata2.todo_content = Some("Session 2 tasks".to_string());
+    let todo_state2 = TodoState::new("Session 2 tasks".to_string());
+    todo_state2
+        .to_extension_data(&mut metadata2.extension_data)
+        .unwrap();
     goose::session::storage::update_metadata(&session2_path, &metadata2)
         .await
         .unwrap();
@@ -237,12 +253,16 @@ async fn test_todo_isolation_between_sessions() {
     let metadata1_read = goose::session::storage::read_metadata(&session1_path).unwrap();
     let metadata2_read = goose::session::storage::read_metadata(&session2_path).unwrap();
 
-    assert_eq!(metadata1_read.todo_content.unwrap(), "Session 1 tasks");
-    assert_eq!(metadata2_read.todo_content.unwrap(), "Session 2 tasks");
+    let todo1 = TodoState::from_extension_data(&metadata1_read.extension_data).unwrap();
+    let todo2 = TodoState::from_extension_data(&metadata2_read.extension_data).unwrap();
+
+    assert_eq!(todo1.content, "Session 1 tasks");
+    assert_eq!(todo2.content, "Session 2 tasks");
 }
 
 #[tokio::test]
 async fn test_todo_clear_removes_from_session() {
+    use goose::session::extension_data::{ExtensionState, TodoState};
     let temp_dir = create_test_session_dir().await;
     let session_id = session::Identifier::Name(format!("test_session_{}", Uuid::new_v4()));
     let agent = create_test_agent_with_mock_provider().await;
@@ -250,7 +270,10 @@ async fn test_todo_clear_removes_from_session() {
     // Pre-populate session with TODO content
     let session_path = goose::session::storage::get_path(session_id.clone()).unwrap();
     let mut metadata = SessionMetadata::default();
-    metadata.todo_content = Some("- Task to clear".to_string());
+    let todo_state = TodoState::new("- Task to clear".to_string());
+    todo_state
+        .to_extension_data(&mut metadata.extension_data)
+        .unwrap();
     goose::session::storage::update_metadata(&session_path, &metadata)
         .await
         .unwrap();
@@ -280,18 +303,23 @@ async fn test_todo_clear_removes_from_session() {
     // With mock provider, the TODO won't actually be cleared via tool calls
     // but we can verify the structure is correct
     let metadata_after = goose::session::storage::read_metadata(&session_path).unwrap();
-    assert!(metadata_after.todo_content.is_some()); // Will still have the original content with mock
+    let todo_state_after = TodoState::from_extension_data(&metadata_after.extension_data);
+    assert!(todo_state_after.is_some()); // Will still have the original content with mock
 }
 
 #[tokio::test]
 async fn test_todo_persistence_across_agent_instances() {
+    use goose::session::extension_data::{ExtensionState, TodoState};
     let session_id = session::Identifier::Name(format!("test_session_{}", Uuid::new_v4()));
 
     // First agent instance adds TODO
     {
         let session_path = goose::session::storage::get_path(session_id.clone()).unwrap();
         let mut metadata = SessionMetadata::default();
-        metadata.todo_content = Some("Persistent task".to_string());
+        let todo_state = TodoState::new("Persistent task".to_string());
+        todo_state
+            .to_extension_data(&mut metadata.extension_data)
+            .unwrap();
         goose::session::storage::update_metadata(&session_path, &metadata)
             .await
             .unwrap();
@@ -301,13 +329,14 @@ async fn test_todo_persistence_across_agent_instances() {
     {
         let session_path = goose::session::storage::get_path(session_id.clone()).unwrap();
         let metadata = goose::session::storage::read_metadata(&session_path).unwrap();
-
-        assert_eq!(metadata.todo_content.unwrap(), "Persistent task");
+        let todo_state = TodoState::from_extension_data(&metadata.extension_data).unwrap();
+        assert_eq!(todo_state.content, "Persistent task");
     }
 }
 
 #[tokio::test]
 async fn test_todo_max_chars_limit() {
+    use goose::session::extension_data::{ExtensionState, TodoState};
     let session_id = session::Identifier::Name(format!("test_session_{}", Uuid::new_v4()));
 
     // Set a small limit for testing
@@ -318,7 +347,10 @@ async fn test_todo_max_chars_limit() {
 
     // Try to set content that exceeds the limit
     let long_content = "x".repeat(100);
-    metadata.todo_content = Some(long_content.clone());
+    let todo_state = TodoState::new(long_content.clone());
+    todo_state
+        .to_extension_data(&mut metadata.extension_data)
+        .unwrap();
 
     // This should succeed at the storage level (storage doesn't enforce limits)
     goose::session::storage::update_metadata(&session_path, &metadata)
@@ -334,6 +366,7 @@ async fn test_todo_max_chars_limit() {
 
 #[tokio::test]
 async fn test_todo_with_special_characters() {
+    use goose::session::extension_data::{ExtensionState, TodoState};
     let session_id = session::Identifier::Name(format!("test_session_{}", Uuid::new_v4()));
 
     let session_path = goose::session::storage::get_path(session_id.clone()).unwrap();
@@ -350,18 +383,23 @@ async fn test_todo_with_special_characters() {
 - Task with tab	separation
 "#;
 
-    metadata.todo_content = Some(special_content.to_string());
+    let todo_state = TodoState::new(special_content.to_string());
+    todo_state
+        .to_extension_data(&mut metadata.extension_data)
+        .unwrap();
     goose::session::storage::update_metadata(&session_path, &metadata)
         .await
         .unwrap();
 
     // Read back and verify
     let metadata_read = goose::session::storage::read_metadata(&session_path).unwrap();
-    assert_eq!(metadata_read.todo_content.unwrap(), special_content);
+    let todo_state_read = TodoState::from_extension_data(&metadata_read.extension_data).unwrap();
+    assert_eq!(todo_state_read.content, special_content);
 }
 
 #[tokio::test]
 async fn test_todo_concurrent_access() {
+    use goose::session::extension_data::{ExtensionState, TodoState};
     let session_id = session::Identifier::Name(format!("test_session_{}", Uuid::new_v4()));
 
     // Spawn multiple concurrent TODO operations
@@ -375,8 +413,13 @@ async fn test_todo_concurrent_access() {
             let mut metadata = goose::session::storage::read_metadata(&session_path)
                 .unwrap_or_else(|_| SessionMetadata::default());
 
-            let current_content = metadata.todo_content.unwrap_or_default();
-            metadata.todo_content = Some(format!("{}\n- Task {}", current_content, i));
+            let current_content = TodoState::from_extension_data(&metadata.extension_data)
+                .map(|t| t.content)
+                .unwrap_or_default();
+            let new_todo = TodoState::new(format!("{}\n- Task {}", current_content, i));
+            new_todo
+                .to_extension_data(&mut metadata.extension_data)
+                .unwrap();
 
             goose::session::storage::update_metadata(&session_path, &metadata).await
         });
@@ -392,25 +435,28 @@ async fn test_todo_concurrent_access() {
     // Verify final state contains at least one task
     let session_path = goose::session::storage::get_path(session_id).unwrap();
     let metadata = goose::session::storage::read_metadata(&session_path).unwrap();
-    let todo_content = metadata.todo_content.unwrap();
+    let todo_state = TodoState::from_extension_data(&metadata.extension_data).unwrap();
 
     // Should contain at least one task (concurrent writes may overwrite)
-    assert!(todo_content.contains("Task"));
+    assert!(todo_state.content.contains("Task"));
 }
 
 #[tokio::test]
 async fn test_todo_empty_session_returns_empty() {
+    use goose::session::extension_data::{ExtensionState, TodoState};
     let session_id = session::Identifier::Name(format!("test_session_{}", Uuid::new_v4()));
 
     let session_path = goose::session::storage::get_path(session_id.clone()).unwrap();
     let metadata = goose::session::storage::read_metadata(&session_path)
         .unwrap_or_else(|_| SessionMetadata::default());
 
-    assert!(metadata.todo_content.is_none() || metadata.todo_content.as_ref().unwrap().is_empty());
+    let todo_state = TodoState::from_extension_data(&metadata.extension_data);
+    assert!(todo_state.is_none() || todo_state.unwrap().content.is_empty());
 }
 
 #[tokio::test]
 async fn test_todo_update_preserves_other_metadata() {
+    use goose::session::extension_data::{ExtensionState, TodoState};
     let session_id = session::Identifier::Name(format!("test_session_{}", Uuid::new_v4()));
 
     let session_path = goose::session::storage::get_path(session_id.clone()).unwrap();
@@ -420,14 +466,20 @@ async fn test_todo_update_preserves_other_metadata() {
     metadata.message_count = 5;
     metadata.description = "Test session".to_string();
     metadata.total_tokens = Some(1000);
-    metadata.todo_content = Some("Initial TODO".to_string());
+    let todo_state = TodoState::new("Initial TODO".to_string());
+    todo_state
+        .to_extension_data(&mut metadata.extension_data)
+        .unwrap();
 
     goose::session::storage::update_metadata(&session_path, &metadata)
         .await
         .unwrap();
 
     // Update only TODO content
-    metadata.todo_content = Some("Updated TODO".to_string());
+    let todo_state_updated = TodoState::new("Updated TODO".to_string());
+    todo_state_updated
+        .to_extension_data(&mut metadata.extension_data)
+        .unwrap();
     goose::session::storage::update_metadata(&session_path, &metadata)
         .await
         .unwrap();
@@ -437,5 +489,6 @@ async fn test_todo_update_preserves_other_metadata() {
     assert_eq!(metadata_read.message_count, 5);
     assert_eq!(metadata_read.description, "Test session");
     assert_eq!(metadata_read.total_tokens, Some(1000));
-    assert_eq!(metadata_read.todo_content, Some("Updated TODO".to_string()));
+    let todo_state_read = TodoState::from_extension_data(&metadata_read.extension_data).unwrap();
+    assert_eq!(todo_state_read.content, "Updated TODO");
 }
diff --git a/ui/desktop/openapi.json b/ui/desktop/openapi.json
index 61542bf46a31..4ee811a1ed71 100644
--- a/ui/desktop/openapi.json
+++ b/ui/desktop/openapi.json
@@ -2123,6 +2123,11 @@
           "propertyName": "type"
         }
       },
+      "ExtensionData": {
+        "type": "object",
+        "description": "Extension data containing all extension states\nKeys are in format \"extension_name.version\" (e.g., \"todo.v0\")",
+        "additionalProperties": {}
+      },
       "ExtensionEntry": {
         "allOf": [
           {
@@ -3207,6 +3212,9 @@
             "type": "string",
             "description": "A short description of the session, typically 3 words or less"
           },
+          "extension_data": {
+            "$ref": "#/components/schemas/ExtensionData"
+          },
           "input_tokens": {
             "type": "integer",
             "format": "int32",
@@ -3229,11 +3237,6 @@
             "description": "ID of the schedule that triggered this session, if any",
             "nullable": true
           },
-          "todo_content": {
-            "type": "string",
-            "description": "Session-scoped TODO list content",
-            "nullable": true
-          },
           "total_tokens": {
             "type": "integer",
             "format": "int32",
diff --git a/ui/desktop/src/api/types.gen.ts b/ui/desktop/src/api/types.gen.ts
index 76a9e3fcd13b..9d2e4621727f 100644
--- a/ui/desktop/src/api/types.gen.ts
+++ b/ui/desktop/src/api/types.gen.ts
@@ -279,6 +279,14 @@ export type ExtensionConfig = {
     type: 'inline_python';
 };
 
+/**
+ * Extension data containing all extension states
+ * Keys are in format "extension_name.version" (e.g., "todo.v0")
+ */
+export type ExtensionData = {
+    [key: string]: unknown;
+};
+
 export type ExtensionEntry = ExtensionConfig & {
     type?: 'ExtensionEntry';
 } & {
@@ -682,6 +690,7 @@ export type SessionMetadata = {
      * A short description of the session, typically 3 words or less
      */
     description: string;
+    extension_data?: ExtensionData;
     /**
      * The number of input tokens used in the session. Retrieved from the provider's last usage.
      */
@@ -698,10 +707,6 @@ export type SessionMetadata = {
      * ID of the schedule that triggered this session, if any
      */
     schedule_id?: string | null;
-    /**
-     * Session-scoped TODO list content
-     */
-    todo_content?: string | null;
     /**
      * The total number of tokens used in the session. Retrieved from the provider's last usage.
      */