refactor: extract shared sandbox and gateway plumbing

src/agents/sandbox/test-args.ts

@@ -0,0 +1,15 @@
+export function findDockerArgsCall(calls: unknown[][], command: string): string[] | undefined {
+  return calls.find((call) => Array.isArray(call[0]) && call[0][0] === command)?.[0] as
+    | string[]
+    | undefined;
+}
+
+export function collectDockerFlagValues(args: string[], flag: string): string[] {
+  const values: string[] = [];
+  for (let i = 0; i < args.length; i += 1) {
+    if (args[i] === flag && typeof args[i + 1] === "string") {
+      values.push(args[i + 1]);
+    }
+  }
+  return values;
+}