diff --git a/src/acp/pool.rs b/src/acp/pool.rs
index e1d27bf..08b55a2 100644
--- a/src/acp/pool.rs
+++ b/src/acp/pool.rs
@@ -3,6 +3,7 @@ use crate::acp::protocol::ConfigOption;
 use crate::config::AgentConfig;
 use anyhow::{anyhow, Result};
 use std::collections::HashMap;
+use std::path::{Path, PathBuf};
 use std::sync::Arc;
 use tokio::sync::{Mutex, RwLock};
 use tokio::time::Instant;
@@ -28,6 +29,7 @@ pub struct SessionPool {
     state: RwLock<PoolState>,
     config: AgentConfig,
     max_sessions: usize,
+    mapping_path: PathBuf,
 }
 
 type EvictionCandidate = (
@@ -63,15 +65,42 @@ fn get_or_insert_gate(
 
 impl SessionPool {
     pub fn new(config: AgentConfig, max_sessions: usize) -> Self {
+        let mapping_path = PathBuf::from(&config.working_dir).join("thread_map.json");
+        let suspended = Self::load_mapping(&mapping_path);
         Self {
             state: RwLock::new(PoolState {
                 active: HashMap::new(),
                 cancel_handles: HashMap::new(),
-                suspended: HashMap::new(),
+                suspended,
                 creating: HashMap::new(),
             }),
             config,
             max_sessions,
+            mapping_path,
+        }
+    }
+
+    fn load_mapping(path: &Path) -> HashMap<String, String> {
+        match std::fs::read_to_string(path) {
+            Ok(data) => serde_json::from_str(&data).unwrap_or_else(|e| {
+                warn!(path = %path.display(), error = %e, "corrupt thread_map.json, starting fresh");
+                HashMap::new()
+            }),
+            Err(_) => HashMap::new(),
+        }
+    }
+
+    fn save_mapping(&self, suspended: &HashMap<String, String>) {
+        let data = match serde_json::to_string_pretty(suspended) {
+            Ok(d) => d,
+            Err(e) => {
+                warn!(error = %e, "failed to serialize thread mapping");
+                return;
+            }
+        };
+        let tmp = self.mapping_path.with_extension("json.tmp");
+        if let Err(e) = std::fs::write(&tmp, &data).and_then(|_| std::fs::rename(&tmp, &self.mapping_path)) {
+            warn!(path = %self.mapping_path.display(), error = %e, "failed to persist thread mapping");
         }
     }
 
@@ -213,6 +242,7 @@ impl SessionPool {
 
         state.suspended.remove(thread_id);
         state.active.insert(thread_id.to_string(), new_conn);
+        self.save_mapping(&state.suspended);
         if !cancel_session_id.is_empty() {
             state.cancel_handles.insert(thread_id.to_string(), (cancel_handle, cancel_session_id));
         }
@@ -330,12 +360,26 @@ impl SessionPool {
                 }
             }
         }
+        self.save_mapping(&state.suspended);
     }
 
     pub async fn shutdown(&self) {
         let mut state = self.state.write().await;
+        // Collect handles before borrowing suspended mutably.
+        let handles: Vec<(String, Arc<Mutex<AcpConnection>>)> = state
+            .active
+            .iter()
+            .map(|(k, v)| (k.clone(), Arc::clone(v)))
+            .collect();
+        for (key, conn) in handles {
+            let conn = conn.lock().await;
+            if let Some(sid) = conn.acp_session_id.clone() {
+                state.suspended.insert(key, sid);
+            }
+        }
+        self.save_mapping(&state.suspended);
         let count = state.active.len();
-        state.active.clear(); // Drop impl kills process groups
+        state.active.clear();
         info!(count, "pool shutdown complete");
     }
 }