diff --git a/examples/localcowork/src-tauri/src/agent_core/orchestrator.rs b/examples/localcowork/src-tauri/src/agent_core/orchestrator.rs
index 2222db2..b20bcdc 100644
--- a/examples/localcowork/src-tauri/src/agent_core/orchestrator.rs
+++ b/examples/localcowork/src-tauri/src/agent_core/orchestrator.rs
@@ -188,15 +188,17 @@ pub async fn orchestrate_dual_model(
 
     tracing::info!(step_count = plan.steps.len(), "orchestrator: plan created");
 
-    // ── Build tool embedding index ──────────────────────────────────────
+    // ── Build tool embedding index (with cache) ───────────────────────────
     let tool_pairs: Vec<(String, String)> = {
         let mcp = mcp_state.lock().await;
         mcp.registry.tool_name_description_pairs()
     };
 
-    let tool_index = match ToolEmbeddingIndex::build(
+    let cache_dir = crate::cache_dir();
+    let tool_index = match ToolEmbeddingIndex::build_with_cache(
         router.current_base_url(),
         &tool_pairs,
+        Some(&cache_dir),
     )
     .await
     {
@@ -212,7 +214,7 @@ pub async fn orchestrate_dual_model(
         }
     };
 
-    tracing::info!(tool_count = tool_index.len(), "orchestrator: tool index built");
+    tracing::info!(tool_count = tool_index.len(), "orchestrator: tool index ready");
 
     // ── Plan validation gate (Improvement I4) ─────────────────────────
     {
diff --git a/examples/localcowork/src-tauri/src/agent_core/tool_prefilter.rs b/examples/localcowork/src-tauri/src/agent_core/tool_prefilter.rs
index 54afdc5..eb7b0d5 100644
--- a/examples/localcowork/src-tauri/src/agent_core/tool_prefilter.rs
+++ b/examples/localcowork/src-tauri/src/agent_core/tool_prefilter.rs
@@ -4,11 +4,19 @@
 //! endpoint, then for each user query, embeds the query and selects the
 //! top-K tools by cosine similarity.
 //!
+//! Caching: The embedding index can be cached to disk for fast startup.
+//! Cache is invalidated when the model endpoint or tool list changes.
+//!
 //! Ported from TypeScript `tests/model-behavior/benchmark-lfm.ts` (lines 270-414).
 
 use reqwest::Client as HttpClient;
 use serde::{Deserialize, Serialize};
-use std::time::Duration;
+use std::fs;
+use std::path::{Path, PathBuf};
+use std::time::{Duration, SystemTime, UNIX_EPOCH};
+
+#[allow(unused_imports)]
+use std::io::{self, Write};
 
 // ─── Error Type ─────────────────────────────────────────────────────────────
 
@@ -43,6 +51,27 @@ struct EmbeddingResponse {
     data: Vec<RawEmbeddingItem>,
 }
 
+/// Metadata stored alongside the cached index for validation.
+#[derive(Debug, Serialize, Deserialize)]
+struct CacheMetadata {
+    /// Endpoint used to build the index (e.g., "http://localhost:1234/v1")
+    endpoint: String,
+    /// Hash of tool names + descriptions to detect tool changes.
+    tool_hash: String,
+    /// Unix timestamp when the cache was created.
+    created_at: u64,
+    /// Embedding dimension.
+    dimension: usize,
+}
+
+/// Full cache file contents.
+#[derive(Debug, Serialize, Deserialize)]
+struct CachedIndex {
+    metadata: CacheMetadata,
+    tool_names: Vec<String>,
+    embeddings: Vec<Vec<f32>>,
+}
+
 // ─── Tool Embedding Index ───────────────────────────────────────────────────
 
 /// Pre-computed tool embedding index for RAG pre-filtering.
@@ -94,6 +123,143 @@ impl ToolEmbeddingIndex {
         })
     }
 
+    /// Build the index, trying to load from cache first.
+    ///
+    /// If a valid cached index exists (same endpoint + tools), loads it.
+    /// Otherwise builds fresh and saves to cache.
+    pub async fn build_with_cache(
+        endpoint: &str,
+        tools: &[(String, String)],
+        cache_dir: Option<&Path>,
+    ) -> Result<Self, ToolPreFilterError> {
+        // Try to load from cache first
+        if let Some(dir) = cache_dir {
+            if let Ok(cached) = Self::load_from_cache(endpoint, tools, dir) {
+                tracing::info!(
+                    tool_count = cached.len(),
+                    "orchestrator: tool index loaded from cache"
+                );
+                return Ok(cached);
+            }
+        }
+
+        // Build fresh
+        let index = Self::build(endpoint, tools).await?;
+
+        // Save to cache
+        if let Some(dir) = cache_dir {
+            if let Err(e) = index.save_to_cache(endpoint, tools, dir) {
+                tracing::warn!(error = %e, "failed to save tool index cache");
+            } else {
+                tracing::info!("orchestrator: tool index cached");
+            }
+        }
+
+        Ok(index)
+    }
+
+    /// Get the cache file path for a given endpoint.
+    fn cache_path(cache_dir: &Path, endpoint: &str) -> PathBuf {
+        // Create a safe filename from the endpoint
+        let safe_name = endpoint
+            .replace("://", "_")
+            .replace("/", "_")
+            .replace(":", "_")
+            .replace(".", "_");
+        cache_dir.join(format!("tool_index_{}.json", safe_name))
+    }
+
+    /// Load the index from cache if valid.
+    fn load_from_cache(
+        endpoint: &str,
+        tools: &[(String, String)],
+        cache_dir: &Path,
+    ) -> Result<Self, ToolPreFilterError> {
+        let cache_path = Self::cache_path(cache_dir, endpoint);
+
+        if !cache_path.exists() {
+            return Err(ToolPreFilterError::RequestFailed {
+                reason: "cache file not found".to_string(),
+            });
+        }
+
+        let content = fs::read_to_string(&cache_path).map_err(|e| ToolPreFilterError::RequestFailed {
+            reason: format!("failed to read cache: {}", e),
+        })?;
+
+        let cached: CachedIndex = serde_json::from_str(&content).map_err(|e| ToolPreFilterError::RequestFailed {
+            reason: format!("failed to parse cache: {}", e),
+        })?;
+
+        // Validate endpoint
+        if cached.metadata.endpoint != endpoint {
+            return Err(ToolPreFilterError::RequestFailed {
+                reason: "endpoint changed".to_string(),
+            });
+        }
+
+        // Validate tool hash
+        let current_hash = compute_tool_hash(tools);
+        if cached.metadata.tool_hash != current_hash {
+            return Err(ToolPreFilterError::RequestFailed {
+                reason: "tools changed".to_string(),
+            });
+        }
+
+        // Validate embeddings exist
+        if cached.embeddings.is_empty() && !cached.tool_names.is_empty() {
+            return Err(ToolPreFilterError::RequestFailed {
+                reason: "cached embeddings are empty".to_string(),
+            });
+        }
+
+        Ok(Self {
+            tool_names: cached.tool_names,
+            embeddings: cached.embeddings,
+        })
+    }
+
+    /// Save the index to cache.
+    fn save_to_cache(
+        &self,
+        endpoint: &str,
+        tools: &[(String, String)],
+        cache_dir: &Path,
+    ) -> Result<(), ToolPreFilterError> {
+        // Create cache directory if needed
+        fs::create_dir_all(cache_dir).map_err(|e| ToolPreFilterError::RequestFailed {
+            reason: format!("failed to create cache dir: {}", e),
+        })?;
+
+        let dimension = self.embeddings.first().map(|e| e.len()).unwrap_or(0);
+        let created_at = SystemTime::now()
+            .duration_since(UNIX_EPOCH)
+            .map(|d| d.as_secs())
+            .unwrap_or(0);
+
+        let cached = CachedIndex {
+            metadata: CacheMetadata {
+                endpoint: endpoint.to_string(),
+                tool_hash: compute_tool_hash(tools),
+                created_at,
+                dimension,
+            },
+            tool_names: self.tool_names.clone(),
+            embeddings: self.embeddings.clone(),
+        };
+
+        let content = serde_json::to_string_pretty(&cached).map_err(|e| ToolPreFilterError::RequestFailed {
+            reason: format!("failed to serialize cache: {}", e),
+        })?;
+
+        let cache_path = Self::cache_path(cache_dir, endpoint);
+        fs::write(&cache_path, content).map_err(|e| ToolPreFilterError::RequestFailed {
+            reason: format!("failed to write cache: {}", e),
+        })?;
+
+        Ok(())
+    }
+
     /// Select the top-K tool names by cosine similarity to the query.
     ///
     /// Returns `(selected_names, scored_tools)` where scored_tools is sorted
@@ -281,6 +447,21 @@ fn cosine_similarity(a: &[f32], b: &[f32]) -> f32 {
     a.iter().zip(b.iter()).map(|(x, y)| x * y).sum()
 }
 
+/// Compute a hash of the tool list for cache validation.
+///
+/// Uses a simple FNV-like hash for speed.
+fn compute_tool_hash(tools: &[(String, String)]) -> String {
+    use std::collections::hash_map::DefaultHasher;
+    use std::hash::{Hash, Hasher};
+
+    let mut hasher = DefaultHasher::new();
+    for (name, desc) in tools {
+        name.hash(&mut hasher);
+        desc.hash(&mut hasher);
+    }
+    format!("{:x}", hasher.finish())
+}
+
 // ─── Tests ──────────────────────────────────────────────────────────────────
 
 #[cfg(test)]
@@ -359,4 +540,28 @@ mod tests {
         assert_eq!(index.len(), 2);
         assert!(!index.is_empty());
     }
+
+    #[test]
+    fn compute_tool_hash_deterministic() {
+        let tools = vec![
+            ("tool1".to_string(), "description1".to_string()),
+            ("tool2".to_string(), "description2".to_string()),
+        ];
+        let hash1 = compute_tool_hash(&tools);
+        let hash2 = compute_tool_hash(&tools);
+        assert_eq!(hash1, hash2, "same tools should produce same hash");
+    }
+
+    #[test]
+    fn compute_tool_hash_different_for_different_tools() {
+        let tools1 = vec![
+            ("tool1".to_string(), "description1".to_string()),
+        ];
+        let tools2 = vec![
+            ("tool2".to_string(), "description2".to_string()),
+        ];
+        let hash1 = compute_tool_hash(&tools1);
+        let hash2 = compute_tool_hash(&tools2);
+        assert_ne!(hash1, hash2, "different tools should produce different hashes");
+    }
 }
diff --git a/examples/localcowork/src-tauri/src/lib.rs b/examples/localcowork/src-tauri/src/lib.rs
index b8c1de0..7e4cdf7 100644
--- a/examples/localcowork/src-tauri/src/lib.rs
+++ b/examples/localcowork/src-tauri/src/lib.rs
@@ -34,6 +34,11 @@ pub(crate) fn data_dir() -> std::path::PathBuf {
         .join(".localcowork")
 }
 
+/// Returns the cache directory for the app (embedding indexes, etc.).
+pub(crate) fn cache_dir() -> std::path::PathBuf {
+    data_dir().join("cache")
+}
+
 /// Initialize the tracing subscriber — writes structured logs to the app data directory.
 ///
 /// On each app startup: