Cut Windows decode disk I/O from 2.06s/tok to 1.70s/tok (budget=4), meeting the
<=2s/tok target. Two changes on the pread expert-load path:
1. compat.h: replace the posix_fadvise no-op with a real WILLNEED cache-warmer
(overlapped ReadFile into a scratch buffer -> populates the standby page cache
so the later synchronous pread faults from RAM). Re-arms the existing
expert_prefetch/PILOT/next-block prefetch chain on Windows. DONTNEED stays a
no-op (matches macOS; Windows standby-list trimming self-regulates).
Measured: hit rate 16.4% -> 27.6%.
2. glm.c: flip PIPE (async expert-load thread pool) from default OFF to default ON
on Windows. Dispatches expert pread onto worker threads so loads overlap the
matmul, instead of blocking serial load-then-compute. PIPE=0 opts out.
Measured: expert-disk 65.9s -> 54.3s (-18%).
Also adds compat_fadvise assertions to tests/test_compat_direct.c (data integrity
after cache-warmer, safe no-op on bad fd / non-WILLNEED).
mmap (CreateFileMapping/MapViewOfFile) was implemented and tested at length but
reverted: it regressed on Windows (RSS bloat from touched mapped pages collapsed
the expert cache via ullAvailPhys — a fundamental Windows-vs-Linux difference).
Full findings + the dead-end analysis recorded in issue_diskio.md.
woolcoxm
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