ci: apply reviewed Stage C backend fix

Author: TheHiddenObserver

.github/workflows/pr126-stage-c-fix.yml

@@ -0,0 +1,81 @@
+name: PR126 Stage C reviewed fix
+
+on:
+  push:
+    branches: [agent/panel-p1-stage-c-covariance]
+    paths:
+      - '.github/workflows/pr126-stage-c-fix.yml'
+
+permissions:
+  contents: write
+
+jobs:
+  patch:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+        with:
+          ref: agent/panel-p1-stage-c-covariance
+          fetch-depth: 0
+      - uses: actions/setup-python@v5
+        with:
+          python-version: '3.11'
+      - name: Remove HC leverage host-vector transfer
+        run: |
+          python - <<'PY'
+          from pathlib import Path
+
+          path = Path('statgpu/panel/_covariance.py')
+          text = path.read_text(encoding='utf-8')
+          old = '''    leverage_np = np.asarray(_to_numpy(leverage), dtype=np.float64).ravel()
+    tol = 256.0 * np.finfo(np.float64).eps
+    if leverage_np.size and float(np.min(leverage_np)) < -tol:
+        raise ValueError("HC2/HC3 leverage is materially negative")
+    if leverage_np.size and float(np.max(leverage_np)) > 1.0 + tol:
+        raise ValueError("HC2/HC3 leverage is materially greater than one")
+    leverage_np = np.clip(leverage_np, 0.0, 1.0)
+    denominator_np = 1.0 - leverage_np
+    if denominator_np.size and float(np.min(denominator_np)) <= tol:
+        raise ValueError("HC2/HC3 covariance is undefined when leverage is numerically one")
+    denominator = xp_asarray(
+        denominator_np,
+        dtype=xp.float64,
+        xp=xp,
+        ref_arr=X,
+    )
+'''
+          new = '''    leverage_min = _to_float_scalar(xp.min(leverage))
+    leverage_max = _to_float_scalar(xp.max(leverage))
+    tol = 256.0 * np.finfo(np.float64).eps
+    if leverage_min < -tol:
+        raise ValueError("HC2/HC3 leverage is materially negative")
+    if leverage_max > 1.0 + tol:
+        raise ValueError("HC2/HC3 leverage is materially greater than one")
+    if _is_torch(xp):
+        leverage = xp.clamp(leverage, min=0.0, max=1.0)
+    else:
+        leverage = xp.clip(leverage, 0.0, 1.0)
+    denominator = 1.0 - leverage
+    denominator_min = _to_float_scalar(xp.min(denominator))
+    if denominator_min <= tol:
+        raise ValueError("HC2/HC3 covariance is undefined when leverage is numerically one")
+'''
+          if old not in text:
+              raise SystemExit('expected HC leverage block not found')
+          text = text.replace(old, new, 1)
+          text = text.replace(
+              '"leverage_min": float(leverage_np.min()) if leverage_np.size else None,\n                "leverage_max": float(leverage_np.max()) if leverage_np.size else None,',
+              '"leverage_min": float(leverage_min),\n                "leverage_max": float(leverage_max),',
+              1,
+          )
+          path.write_text(text, encoding='utf-8')
+          PY
+          python -m compileall -q statgpu/panel/_covariance.py
+          git diff --check
+      - name: Commit reviewed fix
+        run: |
+          git config user.name 'github-actions[bot]'
+          git config user.email '41898282+github-actions[bot]@users.noreply.github.com'
+          git add statgpu/panel/_covariance.py
+          git commit -m 'fix: keep HC leverage backend-native'
+          git push origin HEAD:agent/panel-p1-stage-c-covariance