nx_read_file_gate.nx

nx_read_file_gate.nx -- referee for sys_read_file / sys_free_file, the estate's whole-file reader. WHY (debt 1787076780, measured 2026-08-17/19): for a file whose size is UNKNOWABLE (lseek END <= 0 -- /proc files, pipes, and every EMPTY regular file, which reports 0 just the same) the reader reserved 4 GiB of address space per call and the paired free could release only what was read. A daemon that read an empty registry every sweep ballooned its VmSize by 4 GiB per read; the leak screens flagged it. 2026-08-19 the size-unknowable path GROWS (64 KiB window, doubling, exact hand-back). These teeth pin: T1 a known-size file reads whole and byte-exact (the path the compiler itself uses -- unchanged) T2 an EMPTY regular file returns a non-NULL buffer with len 0 (present-and-empty is not absent) T3 THE BITE: reading + freeing an empty file 32 times moves VmSize by < 1 MiB (the old reader grew by 4 GiB per read -- 128 GiB here -- and could not shrink back) T4 a size-unknowable /proc file reads whole (procs_blocked, the LAST line of /proc/stat, is present) T5 a size-unknowable file LARGER than the first window (/proc/kallsyms, MBs) reads whole through the doubling path -- precondition: readable on this kernel; SKIP otherwise, never RED T6 sys_free_file on the exact mapping returns 0 (munmap success) and an absent path returns NULL/0 T7 neg-control: the free of NULL is a no-op (returns 0, never a crash) license_tier: ORIGINAL expect_exit: 0