Single implementation of ptrace helpers (pt_*) and inject-path ELF loading (elfldr_load, elfldr_payload_args, elfldr_spawn, elfldr_raise_privileges).

Authid policy

Do not flip ucred authid around every ptrace syscall.

Elevate once for the inject / attach window with:

set_ucred_to_ptrace();  // → PTRACE_AUTHID 0x4800000000010003

That is Sony's SceTracer-style id. DEBUG_AUTHID (…0006) is not accepted for PT_* — using it causes attach/waitpid failures (e.g. errno ECHILD).

Restore the previous authid after the inject window (see inject_elf).

Consumers

Target	Uses
libNineS	`pt_*`, `elfldr_load`, `elfldr_payload_args`
bootstrapper	`elfldr_raise_privileges`
onion_elfldr_server	`elfldr_spawn`, `elfldr_read`
util	`pt_attach` / `pt_mmap` after `set_ucred_to_ptrace()`
daemon	links via NineS

Headers: <onion/pt.h>, <onion/elfldr.h>. Compatibility shims remain under libNineS/include/{pt,elfldr}.h and bootstrapper/include/.