A rejected background spawn produces no process output, so the observed stderr reader the job registry pumps was empty and the model's job_output after such a failure showed only killed before exit, where master's consuming read rendered [stderr] followed by spawn failed: … with the cause. The local providers now serve the note as the whole observed stderr stream once the spawn rejected, and the consuming read still folds it in exactly once, so the model's first read after the failure is byte-identical to master's. ShellProcess.observed and both of its readers are required: every background process exposes offset readers, and the shell tools' pull sources no longer carry a no-readers branch.
Yichen Jiang
3a03d68891