KillOnDrop: SIGTERM process group when tool task is aborted

tokio::spawn abort drops the future but leaves child processes
running as orphans. KillOnDrop sends SIGTERM to the process
group on drop, ensuring cleanup. Defused via mem::forget on
normal completion.

Co-Developed-By: Kent Overstreet <kent.overstreet@linux.dev>

src/agent/tools/bash.rs

@@ -14,6 +14,18 @@ use tokio::io::AsyncReadExt;
 
 use super::{ToolDef, ProcessTracker, default_timeout};
 
+/// RAII guard that SIGTERMs the process group on drop.
+/// Ensures child processes are cleaned up when a task is aborted.
+struct KillOnDrop(u32); // pid
+
+impl Drop for KillOnDrop {
+    fn drop(&mut self) {
+        if self.0 != 0 {
+            unsafe { libc::kill(-(self.0 as i32), libc::SIGTERM); }
+        }
+    }
+}
+
 #[derive(Deserialize)]
 struct Args {
     command: String,
@@ -60,6 +72,7 @@ pub async fn run_bash(args: &serde_json::Value, tracker: &ProcessTracker) -> Res
         .with_context(|| format!("Failed to spawn: {}", command))?;
 
     let pid = child.id().unwrap_or(0);
+    let kill_guard = KillOnDrop(pid);
     tracker.register(pid, command).await;
 
     // Take ownership of stdout/stderr handles before waiting,
@@ -132,6 +145,8 @@ pub async fn run_bash(args: &serde_json::Value, tracker: &ProcessTracker) -> Res
         }
     };
 
+    // Process completed normally — defuse the kill guard
+    std::mem::forget(kill_guard);
     tracker.unregister(pid).await;
     result
 }