Windows: dense-only vindex fails to load (mmap of zero-length file, error 87)

[chrishayuk]

Summary

The dense-only vindex load path fails on Windows only (ubuntu + macos are green). Introduced by #159 (BitNet --dense-only build/load).

test extract::build::tests::dense_only_vindex_loads_without_gate_vectors ... FAILED
thread '...' panicked at crates\larql-vindex\src\extract\build\mod.rs:568:
  dense-only vindex failed to load: Some(Io(Os { code: 87, kind: InvalidInput,
  message: "The parameter is incorrect." }))

Root cause

Windows error 87 (ERROR_INVALID_PARAMETER) is the classic symptom of memmap2::Mmap::map on a 0-byte file: CreateFileMapping rejects a zero size on Windows, whereas Linux/macOS map an empty file fine. The dense-only build skips gate_vectors.bin (and the load path mmaps gate/weight files unconditionally), so a zero-length / empty file reaches an unguarded Mmap::map.

Likely site: crates/larql-vindex/src/format/weights/load/f32.rs (the gate_vectors.bin mmap around the config.quant == None && !opts.skip_ffn branch), but every load-path Mmap::map should be audited — there are several (embeddings.rs, f32.rs).

Suggested fix

Guard the load-path mmaps against zero-length files — skip the mmap (treat as absent / empty) when file.metadata()?.len() == 0. This is correct cross-platform (a 0-byte mapping has no data anyway) and matches how dense-only intentionally omits gate vectors.

Notes

• feat(bitnet): native-ternary 1.58 inference end-to-end (microsoft/bitnet-b1.58-2B-4T) #159 was merged with this red via --admin (all other platforms green) to unblock the bitnet stack; this issue tracks the follow-up.
• Not reproducible on macOS/Linux locally — needs Windows CI to verify a fix.