Make sequential snapin execution opt-in by default

[Copilot]

Sequential snapin execution was being applied by default, but this behavior should remain off for the new snapin ordering feature unless explicitly enabled. This keeps existing multi-snapin behavior intact while preserving ordered execution for opt-in sequential runs.

• Behavior change

  • Gate one-at-a-time snapin dispatch behind the existing abortOnFail / sequential tasking flag.
  • Preserve legacy behavior when the flag is off by returning all eligible snapins in a single response.

• Sequential execution path

  • Keep per-response single-snapin delivery when sequential execution is enabled.
  • Retain the failure-stop behavior for ordered runs so later snapins are not dispatched after an earlier failure.

• Implementation

  • Update SnapinClient to conditionally break after the first queued snapin only when sequential mode is enabled.

$dispatchSequentially = (bool)$SnapinJob->get('abortOnFail');

if ($dispatchSequentially) {
    break;
}