* Align OS argument conversion and syscall handling with Python 3.15
Import canonical os tests through update_lib, retaining existing guards. Preserve raw descriptor validation, errno, audit ordering, signal retries and unlocked sendfile buffers.
Validation: independent source review passed; matching release build and nine bounded canonical cases pending.
Assisted-by: OpenAI Codex:model version unavailable
* Import canonical root-user test support for OS package
Add hash-pinned selective assignment migration within test.support and import the three Python 3.15.0 privilege helpers plus their public exports. Preserve unrelated support helpers and existing test markers.
Validation: 177 host updater tests pass; byte-identical canonical helper provenance verified. Independent source review passed. Native import validation pending integration onto current main.
Assisted-by: OpenAI Codex:model version unavailable
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