feat: add background bash sessions

src/agents/shell-utils.ts

@@ -0,0 +1,41 @@
+import { spawn } from "node:child_process";
+
+export function getShellConfig(): { shell: string; args: string[] } {
+  if (process.platform === "win32") {
+    const shell = process.env.COMSPEC?.trim() || "cmd.exe";
+    return { shell, args: ["/d", "/s", "/c"] };
+  }
+
+  const shell = process.env.SHELL?.trim() || "sh";
+  return { shell, args: ["-c"] };
+}
+
+export function sanitizeBinaryOutput(text: string): string {
+  return text
+    .replace(/[\p{Format}\p{Surrogate}]/gu, "")
+    .replace(/[\x00-\x08\x0B\x0C\x0E-\x1F]/g, "");
+}
+
+export function killProcessTree(pid: number): void {
+  if (process.platform === "win32") {
+    try {
+      spawn("taskkill", ["/F", "/T", "/PID", String(pid)], {
+        stdio: "ignore",
+        detached: true,
+      });
+    } catch {
+      // ignore errors if taskkill fails
+    }
+    return;
+  }
+
+  try {
+    process.kill(-pid, "SIGKILL");
+  } catch {
+    try {
+      process.kill(pid, "SIGKILL");
+    } catch {
+      // process already dead
+    }
+  }
+}