v0.8.8 — Tuning Engine Split & Import Hygiene

📦 Release

• Version sync to 0.8.8 (app + frontend + core): root pyproject.toml,
  frontend/ml-canvas/package.json / package-lock.json, and
  skyulf-core/setup.py bumped to 0.8.8.

🧠 Core — F-18: _tuning/engine.py split (finding closed)

• The 1,830-line skyulf/modeling/_tuning/engine.py (largest file in the
  library) is now a ~700-line orchestrator plus six leaf modules:
  params.py (search-space cleaning, param splitting, model instantiation,
  seed overlays), splitters.py (CV splitter builder family), metrics.py
  (metric validation/aliases, resolve_metric/resolve_scorer with
  pos_label pinning), grid_random.py (candidate generation + per-fold
  scoring), refit.py (best-model refit + decision-threshold tuning), and a
  strategies/ package (halving.py, optuna.py with the F-14 lazy
  loader, runner.py).
• Pure code movement — the public TuningCalculator/TuningApplier surface
  is untouched, test-pinned private methods remain as one-line delegates,
  and stale test pins were retargeted to the new modules with the same
  coverage.

🧹 Core — F-11: import cycles & deferred imports (finding closed)

• One real import cycle broken (modeling/base → _evaluation → sklearn_wrapper → base): the four _evaluation modules now import
  SklearnBridge from the leaf engines.sklearn_bridge, so base.py
  imports its evaluation/cross-validation dependencies at module level.
• 173 function-level imports eliminated (ruff PLC0415): 144 hoisted to
  module level (internal, stdlib, hard dependencies incl. all 93 deferred
  polars imports), 29 genuinely optional extras (matplotlib, rich, shap,
  optuna, imblearn, sentence_transformers, vaderSentiment, causallearn, h3,
  scatter_matrix) kept deferred with documented per-site
  # noqa: PLC0415 - <reason> waivers.
• Enforcement: PLC0415 is now in the ruff select set for
  skyulf-core/skyulf/ (backend/tests/entry points exempt), with the ruff
  pin bumped to >=0.15,<1.0 to match the pre-commit hook.
• Monkeypatch-safe: third-party calls patched by tests keep
  module-attribute form (sklearn_metrics.*, scipy_stats.*,
  stattools.adfuller); degradation gates (SKLEARN_AVAILABLE etc.)
  untouched. Failures now surface at import time, and the real module graph
  is visible for the upcoming F-09/F-08 structural work.

🧾 Housekeeping

• Findings tracker: with F-18 + F-11 closed, 3 findings remain open
  (F-30 deferred pending a compat call; structural F-09/F-08).
• README refresh.

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