diff --git a/server/src/agents/pty.rs b/server/src/agents/pty.rs
index e2d1417e..ef6fb906 100644
--- a/server/src/agents/pty.rs
+++ b/server/src/agents/pty.rs
@@ -245,13 +245,16 @@ fn run_agent_pty_blocking(
     // via recv_timeout: if no output arrives within the configured window
     // the process is killed and the agent is marked Failed.
     let (line_tx, line_rx) = std::sync::mpsc::channel::<std::io::Result<String>>();
-    std::thread::spawn(move || {
+    let sid_for_reader = story_id.to_string();
+    let aname_for_reader = agent_name.to_string();
+    let reader_handle = std::thread::spawn(move || {
         let buf_reader = BufReader::new(reader);
         for line in buf_reader.lines() {
             if line_tx.send(line).is_err() {
                 break;
             }
         }
+        slog!("[agent:{sid_for_reader}:{aname_for_reader}] Reader thread exiting");
     });
 
     let timeout_dur = if inactivity_timeout_secs > 0 {
@@ -424,6 +427,15 @@ fn run_agent_pty_blocking(
     let _ = child.kill();
     let _ = child.wait();
 
+    // Wait for the reader thread to finish so it releases the cloned PTY
+    // master fd before we return.  Without this, the next PTY spawn for the
+    // same story can collide with a still-open fd from this session (#453).
+    slog!("[agent:{story_id}:{agent_name}] Waiting for reader thread to exit");
+    if let Err(e) = reader_handle.join() {
+        slog!("[agent:{story_id}:{agent_name}] Reader thread panicked: {e:?}");
+    }
+    slog!("[agent:{story_id}:{agent_name}] Reader thread joined");
+
     slog!(
         "[agent:{story_id}:{agent_name}] Done. Session: {:?}",
         session_id