fix(tools): implement per-task cancellation for background delegate tasks

cancel_task previously only updated the JSON result file but did not
actually cancel the running tokio task. The CancellationToken was shared
across all background tasks, so there was no way to cancel an individual
task without cancelling all of them.

This fix adds a per-task token registry (task_tokens) that maps each
task_id to its dedicated CancellationToken. When cancel_task is called,
it cancels only the specific task's token, which the spawned task
monitors via tokio::select!. Tokens are cleaned up automatically when
tasks complete.

src/config/schema.rs

@@ -9275,7 +9275,6 @@ mod tests {
     use std::os::unix::fs::PermissionsExt;
     use std::path::PathBuf;
     use std::sync::{Arc, Mutex as StdMutex};
-    #[cfg(unix)]
     use tempfile::TempDir;
     use tokio::sync::{Mutex, MutexGuard};
     use tokio::test;
@@ -13671,12 +13670,12 @@ require_otp_to_resume = true
     async fn ensure_bootstrap_files_creates_missing_files() {
         let tmp = TempDir::new().unwrap();
         let ws = tmp.path().join("workspace");
-        tokio::fs::create_dir_all(&ws).await.unwrap();
+        let _: () = tokio::fs::create_dir_all(&ws).await.unwrap();
 
         ensure_bootstrap_files(&ws).await.unwrap();
 
-        let soul = tokio::fs::read_to_string(ws.join("SOUL.md")).await.unwrap();
-        let identity = tokio::fs::read_to_string(ws.join("IDENTITY.md"))
+        let soul: String = tokio::fs::read_to_string(ws.join("SOUL.md")).await.unwrap();
+        let identity: String = tokio::fs::read_to_string(ws.join("IDENTITY.md"))
             .await
             .unwrap();
         assert!(soul.contains("SOUL.md"));
@@ -13687,21 +13686,21 @@ require_otp_to_resume = true
     async fn ensure_bootstrap_files_does_not_overwrite_existing() {
         let tmp = TempDir::new().unwrap();
         let ws = tmp.path().join("workspace");
-        tokio::fs::create_dir_all(&ws).await.unwrap();
+        let _: () = tokio::fs::create_dir_all(&ws).await.unwrap();
 
         let custom = "# My custom SOUL";
-        tokio::fs::write(ws.join("SOUL.md"), custom).await.unwrap();
+        let _: () = tokio::fs::write(ws.join("SOUL.md"), custom).await.unwrap();
 
         ensure_bootstrap_files(&ws).await.unwrap();
 
-        let soul = tokio::fs::read_to_string(ws.join("SOUL.md")).await.unwrap();
+        let soul: String = tokio::fs::read_to_string(ws.join("SOUL.md")).await.unwrap();
         assert_eq!(
             soul, custom,
             "ensure_bootstrap_files must not overwrite existing files"
         );
 
         // IDENTITY.md should still be created since it was missing
-        let identity = tokio::fs::read_to_string(ws.join("IDENTITY.md"))
+        let identity: String = tokio::fs::read_to_string(ws.join("IDENTITY.md"))
             .await
             .unwrap();
         assert!(identity.contains("IDENTITY.md"));

src/tools/mod.rs

@@ -106,6 +106,9 @@ pub use cron_runs::CronRunsTool;
 pub use cron_update::CronUpdateTool;
 pub use data_management::DataManagementTool;
 pub use delegate::DelegateTool;
+// Re-exported for downstream consumers of background delegation results.
+#[allow(unused_imports)]
+pub use delegate::{BackgroundDelegateResult, BackgroundTaskStatus};
 pub use file_edit::FileEditTool;
 pub use file_read::FileReadTool;
 pub use file_write::FileWriteTool;