feat(#1192): spawn bash tasks with nice(10)

hive-bash-mcp/Cargo.toml

@@ -9,6 +9,7 @@ workspace = true
 [dependencies]
 anyhow.workspace = true
 hive-sh4re.workspace = true
+libc.workspace = true
 rmcp.workspace = true
 schemars.workspace = true
 serde.workspace = true

hive-bash-mcp/src/runner.rs

@@ -358,12 +358,21 @@ async fn exec_cmd(
     timeout: Duration,
 ) -> Result<(i32, bool)> {
     use tokio::process::Command;
-    let mut child = Command::new("sh")
+    // SAFETY: `nice` is async-signal-safe and modifies only the calling
+    // process's scheduling priority before exec. No allocations, no locks.
+    let mut cmd_builder = Command::new("sh");
+    cmd_builder
         .arg("-c")
         .arg(cmd)
         .stdout(std::process::Stdio::piped())
-        .stderr(std::process::Stdio::piped())
-        .spawn()?;
+        .stderr(std::process::Stdio::piped());
+    unsafe {
+        cmd_builder.pre_exec(|| {
+            libc::nice(10);
+            Ok(())
+        });
+    }
+    let mut child = cmd_builder.spawn()?;
 
     let stdout = child.stdout.take().expect("stdout piped");
     let stderr = child.stderr.take().expect("stderr piped");