CUBELinux-2: WordFlags/tri-channel 16-bit flag field, tag-14 + scan_by_word_flag, cubetrace capture→replay→golden→lineage, CUBE VP-tree balling index (cubecode::ballindex), cubefs-visible WordFlags, and cube-mvw (sharded multi-writer MVCC store with per-shard WALs + group-commit + compaction, impl CubeBackend => CubeStore<MvwBackend> DB). Adds show-flags/scan-word-flags/trace-*/golden-capture CLI; ~ tests green.

cube-mvw/src/main.rs

@@ -0,0 +1,35 @@
+use cube_mvw::MvwBackend;
+use cubecoords::Czyx;
+use std::path::Path;
+use std::time::Instant;
+use std::thread;
+
+fn bench(mode: &str) -> f64 {
+    let b = Path::new("/tmp/mvw-gc");
+    for i in 0..16 { std::fs::remove_file(format!("{}-s{}.log", b.display(), i)).ok(); std::fs::remove_file(format!("{}-s{}.ckpt", b.display(), i)).ok(); }
+    let back = MvwBackend::open(16, b).unwrap();
+    let threads = 8usize; let per = 4000u64; let n = (threads as f64) * per as f64;
+    let t = Instant::now();
+    thread::scope(|sc| {
+        for th in 0..threads {
+            let back = &back;
+            sc.spawn(move || for i in 0..per {
+                let k = Czyx::unpack_u32(((th as u64 * per + i) as u32) << 8 | 1);
+                back.put_shared(k, vec![i as u8; 16]);
+            });
+        }
+    });
+    if mode == "batch" { back.commit().unwrap(); }
+    let s = t.elapsed().as_secs_f64();
+    for i in 0..16 { std::fs::remove_file(format!("{}-s{}.log", b.display(), i)).ok(); std::fs::remove_file(format!("{}-s{}.ckpt", b.display(), i)).ok(); }
+    n / s / 1e3
+}
+fn main() {
+    let per_op = bench("per_op");
+    let batch = bench("batch");
+    println!("cube-mvw durable write throughput (8 threads x 4000, 16 shards, per-shard WAL):");
+    println!("  per-op  fsync    : {:>8.1} k puts/s", per_op);
+    println!("  group-commit     : {:>8.1} k puts/s   ({:.1}x)", batch, batch/per_op);
+    println!("\n=> group-commit batches one fsync per shard for many ops => durable writes scale with the");
+    println!("   batch (no tables layer — pure storage engine; CUBE's metatag model is the schema).");
+}