fix: minimize TOCTOU window — reset_session before rename on failure path

Address 擺渡 F1: on ws failure, call reset_session immediately to
kill the session before doing rename_thread I/O. This shrinks the
race window where a concurrent message could hit the doomed session.

Title is still applied on both success and failure paths (per 主人's
requirement), but failure path now does reset first.

Author: chaodu-agent

src/dispatch.rs

@@ -697,20 +697,19 @@ async fn dispatch_batch(
     if created_now {
         if let Some(pr) = parse_result {
             if !pr.metadata.raw.is_empty() {
-                // Apply [[title:...]] override before ws check — title is independent.
-                if let Some(title) = &pr.metadata.title {
-                    if !title.is_empty() {
-                        if let Err(e) = adapter.rename_thread(&dispatch_channel, title).await {
-                            warn!(session_key, error = %e, "failed to apply title directive");
-                        }
-                    }
-                }
+                // Apply [[title:...]] independently — works regardless of ws outcome.
+                let title_to_apply = pr.metadata.title.clone();
 
                 // If workspace resolution failed on a NEW session, rollback and abort.
-                // The session was created with default cwd — we must not leave it alive
-                // when the user explicitly requested a different workspace (ADR §3.1).
+                // Reset FIRST to minimize TOCTOU window (擺渡 F1), then rename.
                 if let Some(Err(e)) = ws_resolved {
                     target.reset_session(&session_key).await;
+                    // Apply title after reset so the thread is identifiable.
+                    if let Some(ref title) = title_to_apply {
+                        if !title.is_empty() {
+                            let _ = adapter.rename_thread(&dispatch_channel, title).await;
+                        }
+                    }
                     let _ = adapter
                         .send_message(&dispatch_channel, &format!("⚠️ {e}"))
                         .await;
@@ -722,6 +721,15 @@ async fn dispatch_batch(
                 if let Some(first_msg) = batch.first_mut() {
                     first_msg.prompt = pr.prompt;
                 }
+
+                // Apply title on success path.
+                if let Some(ref title) = title_to_apply {
+                    if !title.is_empty() {
+                        if let Err(e) = adapter.rename_thread(&dispatch_channel, title).await {
+                            warn!(session_key, error = %e, "failed to apply title directive");
+                        }
+                    }
+                }
             }
         }
     }