Expose the bwrap command line at /run/agent-sandbox inside every sandbox

tests/e2e/mounts.rs

@@ -373,6 +373,7 @@ fn blacklist_overlays_survive_absolute_var_run_symlink() {
     // layout inside the sandbox to reproduce on any host.
     let _guard = HostGlobsLock::for_scan();
     let mut bwrap_args = build_bwrap_command(&["--blacklist", "--no-seccomp", "--", "true"]);
+    strip_command_line_bind(&mut bwrap_args);
     inject_absolute_var_run_symlink(&mut bwrap_args);
 
     let output = Command::new(&bwrap_args[0])
@@ -568,6 +569,15 @@ fn rand_suffix() -> String {
     format!("{nanos:08x}")
 }
 
+// The bind reads from an fd that only exists in the agent-sandbox process.
+fn strip_command_line_bind(bwrap_args: &mut Vec<String>) {
+    let start = bwrap_args
+        .iter()
+        .position(|a| a == "--ro-bind-data")
+        .expect("dry-run output should bind the bwrap command line");
+    bwrap_args.drain(start..start + 3);
+}
+
 fn inject_absolute_var_run_symlink(bwrap_args: &mut Vec<String>) {
     assert_eq!(bwrap_args[1], "--ro-bind");
     assert_eq!(bwrap_args[2], "/");