diff --git a/crates/codegen/xai-grok-workspace/src/file_system/mod.rs b/crates/codegen/xai-grok-workspace/src/file_system/mod.rs
index 50e02fe2..fecb6645 100644
--- a/crates/codegen/xai-grok-workspace/src/file_system/mod.rs
+++ b/crates/codegen/xai-grok-workspace/src/file_system/mod.rs
@@ -34,6 +34,9 @@ pub use fs::{AsyncFileSystem, AsyncFsWrapper, FsError, bytes_to_string};
 mod local_fs;
 pub use local_fs::LocalFs;
 
+mod runtime_fs;
+pub use runtime_fs::RuntimeFs;
+
 mod mock_fs;
 pub use mock_fs::MockFs;
 
diff --git a/crates/codegen/xai-grok-workspace/src/file_system/runtime_fs.rs b/crates/codegen/xai-grok-workspace/src/file_system/runtime_fs.rs
new file mode 100644
index 00000000..d51d03d1
--- /dev/null
+++ b/crates/codegen/xai-grok-workspace/src/file_system/runtime_fs.rs
@@ -0,0 +1,79 @@
+//! Workspace filesystem adapter backed by the Simplicio Runtime.
+//!
+//! Project content must not be read, written, or deleted through the host
+//! filesystem. The tools crate owns the Runtime/Agent handshake; this thin
+//! adapter lets workspace session state use the same fail-closed boundary.
+
+use std::path::{Path, PathBuf};
+
+use crate::file_system::{AsyncFileSystem, FsError};
+use xai_grok_tools::computer::types::AsyncFileSystem as ToolAsyncFileSystem;
+use xai_grok_tools::computer::local::SimplicioRuntimeFs;
+
+/// Workspace filesystem whose project effects are delegated to Runtime.
+pub struct RuntimeFs {
+    root: PathBuf,
+    runtime: SimplicioRuntimeFs,
+}
+
+impl RuntimeFs {
+    pub fn new(root: PathBuf) -> Self {
+        Self {
+            runtime: SimplicioRuntimeFs::new(root.clone()),
+            root,
+        }
+    }
+
+    fn map_error(error: xai_grok_tools::computer::types::ComputerError) -> FsError {
+        FsError::Other(format!("Simplicio Runtime denied workspace operation: {error}"))
+    }
+
+    fn is_not_found(error: &xai_grok_tools::computer::types::ComputerError) -> bool {
+        let message = error.to_string().to_ascii_lowercase();
+        message.contains("not found") || message.contains("resource_not_found")
+    }
+}
+
+#[async_trait::async_trait]
+impl AsyncFileSystem for RuntimeFs {
+    fn root(&self) -> &Path {
+        &self.root
+    }
+
+    async fn exists(&self, path: &Path) -> Result<bool, FsError> {
+        match self.runtime.stat_workspace(path).await {
+            Ok(_) => Ok(true),
+            Err(error) if Self::is_not_found(&error) => Ok(false),
+            Err(error) => Err(Self::map_error(error)),
+        }
+    }
+
+    async fn read_file(&self, path: &Path) -> Result<Vec<u8>, FsError> {
+        self.runtime
+            .read_file(path)
+            .await
+            .map_err(Self::map_error)
+    }
+
+    async fn try_read_file(&self, path: &Path) -> Result<Option<Vec<u8>>, FsError> {
+        match self.runtime.read_file(path).await {
+            Ok(bytes) => Ok(Some(bytes)),
+            Err(error) if Self::is_not_found(&error) => Ok(None),
+            Err(error) => Err(Self::map_error(error)),
+        }
+    }
+
+    async fn write_file(&self, path: &Path, data: &[u8]) -> Result<(), FsError> {
+        self.runtime
+            .write_file(path, data)
+            .await
+            .map_err(Self::map_error)
+    }
+
+    async fn delete_file(&self, path: &Path) -> Result<(), FsError> {
+        self.runtime
+            .delete_file(path)
+            .await
+            .map_err(Self::map_error)
+    }
+}
diff --git a/crates/codegen/xai-grok-workspace/src/session/mod.rs b/crates/codegen/xai-grok-workspace/src/session/mod.rs
index 4e9ac2c7..efbbec19 100644
--- a/crates/codegen/xai-grok-workspace/src/session/mod.rs
+++ b/crates/codegen/xai-grok-workspace/src/session/mod.rs
@@ -7,7 +7,7 @@ pub(crate) mod swap_policy;
 pub mod tool_config;
 use crate::capability::CapabilityMode;
 use crate::config::{MemoryConfig, SessionContextFactory};
-use crate::file_system::{AsyncFsWrapper, LocalFs};
+use crate::file_system::{AsyncFsWrapper, LocalFs, RuntimeFs};
 use crate::hub::{HubConfig, HubHandle};
 use crate::session::file_state::FileStateTracker;
 use parking_lot::RwLock;
@@ -165,7 +165,14 @@ impl WorkspaceSession {
             Some((handle, rx)) => (Some(handle), Some(rx)),
             None => (None, None),
         };
-        let async_fs = AsyncFsWrapper::new(Arc::new(LocalFs::new(cwd.clone())));
+        // Unit tests use LocalFs fixtures because they do not start the
+        // independent Agent host. Every production session uses RuntimeFs;
+        // project content therefore fails closed when Agent/Runtime is absent.
+        let async_fs = if cfg!(test) {
+            AsyncFsWrapper::new(Arc::new(LocalFs::new(cwd.clone())))
+        } else {
+            AsyncFsWrapper::new(Arc::new(RuntimeFs::new(cwd.clone())))
+        };
         let file_state_tracker = Arc::new(FileStateTracker::new());
         let checkpoint_store =
             crate::session::checkpoint_store::CheckpointStore::new(&cwd, &session_id);