spb/metrika Public

- mlx-swift dependency in ZQGPU (the only module allowed to import MLX)
- Philox4x32-10 as vectorized MLX uint64 ops with the reference key
  schedule: GPU resample indices are bit-identical to the CPU generator
  (asserted per replicate) — the §5 reproducibility contract
- batched gather + float32 cross-products on GPU, float64 Cholesky solves
  on CPU (§5 hybrid); chunked to the memory budget
- conditioning: predictors standardized by fixed full-sample mean/scale
  (exact reparametrization) before forming X'X — raw data with an
  intercept lost 2-3 digits in float32
- MLX workaround: batched GEMM mis-accumulates small k x k outputs at
  batch >= 2 (~6e-4 rel, stride/fusion-independent); X'X is built one
  column at a time through the exact (count,k,n)@(count,n,1) path, with
  regression tests pinning the behavior
- planner: gpuAvailable detected from actual metallib presence (SwiftPM
  CLI cannot compile Metal shaders - swift test skips GPU suites, the
  xcodebuild-built app and tests get the GPU); reps >= 500 dispatches
  bootstrap to .gpu
- engine: backend-aware bootstrap, drops singular resamples, output
  titled 'GPU batched' with gpu scalar
- 68 tests green under xcodebuild (66 + GPU suites under swift test skip)

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

- MetrikaKit SPM package: ZQParser, ZQPlanner, ZQEngine, ZQData, ZQStats,
  ZQGPU, ZQGraphics, ZQPlugins (Swift 6, strict concurrency)
- ZQL parser: lexer, Pratt expressions, factor variables, prefix commands,
  column-cited errors with Levenshtein verb suggestions
- ZQData: DuckDB-backed load/save (parquet, csv, json, arrow)
- ZQStats: OLS via LAPACK QR, HC0-HC3 and cluster-robust SE, summarize,
  t/F distributions accurate in the far tails
- ZQGPU: Philox4x32-10 reference RNG, counter-addressable bootstrap
- ZQEngine: session actor with use/save/gen/replace/drop/keep/summarize/
  regress/count/list/graph/bootstrap/set seed/xtset/log
- SwiftUI app (xcodegen): console with history, variables sidebar,
  Swift Charts plots; sandboxed + hardened runtime entitlements
- Tests: 44 green (parser golden, R fixtures at 1e-10, Philox KAT,
  end-to-end engine); Tests/Fixtures/generate.R; Tests/Bench harness
- scripts: check_headers.sh + pre-commit hook, make_icns.sh, release.sh

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>