Add DC-bias C_eff stima to derating and INFO when bulk C has no HF ceramic.

Keep both as labelled estimates: no Murata lot curve and no invented Z(f) target without f_sw.

Co-authored-by: Cursor <cursoragent@cursor.com>

tests/test_derating.py

@@ -0,0 +1,109 @@
+"""DC-bias C_eff stima — not a Murata lot curve.
+
+Favor: C0G stays at C; X7R at 50% Vr loses ~30%; C_eff formatted.
+Against: tantalum uses C_nom (no MLCC model); missing Vr or C skips C_eff;
+C0G is not treated as X7R.
+"""
+
+from __future__ import annotations
+
+from backend.pinscopex.derating import (
+    build_derating_table,
+    dc_bias_remaining,
+)
+from backend.pinscopex.models import (
+    CapacitorSpecs,
+    Component,
+    ComponentType,
+    DesignGraph,
+    Net,
+    NetType,
+    PinConnection,
+)
+
+
+def test_c0g_keeps_full_capacitance():
+    assert dc_bias_remaining("C0G", v_op=16.0, rated_v=16.0) == 1.0
+    assert dc_bias_remaining("NP0", v_op=10.0, rated_v=16.0) == 1.0
+
+
+def test_x7r_at_half_rated_is_about_70_percent():
+    f = dc_bias_remaining("X7R", v_op=8.0, rated_v=16.0)
+    assert f is not None
+    assert 0.65 <= f <= 0.75
+
+
+def test_x7r_at_zero_bias_is_nominal():
+    assert dc_bias_remaining("X7R", v_op=0.0, rated_v=16.0) == 1.0
+
+
+def test_tantalum_has_no_mlcc_bias_model():
+    assert dc_bias_remaining("tantalum", v_op=8.0, rated_v=16.0) is None
+
+
+def test_missing_voltage_or_value_skips_c_eff():
+    assert dc_bias_remaining("X7R", v_op=None, rated_v=16.0) is None
+    assert dc_bias_remaining("X7R", v_op=8.0, rated_v=None) is None
+
+
+def _cap(ref, dielectric, farads, rated, net="3V3"):
+    return Component(
+        reference=ref, value="", footprint="",
+        component_type=ComponentType.CAPACITOR,
+        component_subtype="passive.capacitor.ceramic",
+        mpn=ref,
+        pins={"1": net, "2": "GND"},
+        specs=CapacitorSpecs(
+            value_farads=farads,
+            value_formatted="10uF",
+            voltage_rating_v=f"{rated}V",
+            dielectric=dielectric,
+        ),
+    )
+
+
+def test_derating_row_includes_c_eff_stima():
+    c1 = _cap("C1", "X7R", 10e-6, 16)
+    g = DesignGraph(
+        components={
+            "C1": c1,
+        },
+        nets={
+            "3V3": Net(
+                name="3V3", net_type=NetType.POWER, voltage=8.0,
+                pins=[PinConnection(component_ref="C1", pin_number="1")],
+            ),
+            "GND": Net(
+                name="GND", net_type=NetType.GROUND, voltage=0.0,
+                pins=[PinConnection(component_ref="C1", pin_number="2")],
+            ),
+        },
+    )
+    rows = build_derating_table(g)
+    assert len(rows) == 1
+    row = rows[0]
+    assert row["dc_bias_model"] == "stima"
+    assert row["c_nominal_f"] == 10e-6
+    assert row["c_eff_f"] is not None
+    assert 6.5e-6 <= row["c_eff_f"] <= 7.5e-6
+    assert "uF" in (row["c_eff_formatted"] or "")
+
+
+def test_c0g_row_c_eff_equals_nominal():
+    c1 = _cap("C9", "C0G", 18e-12, 50)
+    g = DesignGraph(
+        components={"C9": c1},
+        nets={
+            "3V3": Net(
+                name="3V3", net_type=NetType.POWER, voltage=3.3,
+                pins=[PinConnection(component_ref="C9", pin_number="1")],
+            ),
+            "GND": Net(
+                name="GND", net_type=NetType.GROUND,
+                pins=[PinConnection(component_ref="C9", pin_number="2")],
+            ),
+        },
+    )
+    row = build_derating_table(g)[0]
+    assert row["c_eff_f"] == 18e-12
+    assert row["dc_bias_factor"] == 1.0

tests/test_eval_report.py

@@ -85,8 +85,9 @@ def test_simple_project_eval_matches_committed_golden():
     assert scores.graph_ok, scores.graph_errors
     assert scores.precision == 1.0
     assert scores.recall == 1.0
-    assert scores.finding_count == 2
+    assert scores.finding_count == 3
     assert scores.by_status["WARNING"] == 2
+    assert scores.by_status["INFO"] == 1
 
 
 def test_simple_project_eval_rejects_truncated_graph(tmp_path: Path):

tests/test_hf_coverage_check.py

@@ -0,0 +1,93 @@
+"""HF coverage INFO when bulk C exists without a 100 nF-class ceramic."""
+
+from backend.pinscopex.hf_coverage_check import check_hf_decoupling_coverage
+from backend.pinscopex.models import (
+    CapacitorSpecs,
+    Component,
+    ComponentConstraints,
+    ComponentType,
+    DesignGraph,
+    Net,
+    NetType,
+    Pin,
+    PinConnection,
+)
+
+
+def _graph(components, nets):
+    net_objs = {
+        name: Net(
+            name=name, net_type=ntype,
+            pins=[PinConnection(component_ref=r, pin_number=str(p)) for r, p in conns],
+        )
+        for name, (ntype, conns) in nets.items()
+    }
+    return DesignGraph(components=components, nets=net_objs)
+
+
+def _ic():
+    return Component(
+        reference="U1", value="", footprint="",
+        component_type=ComponentType.IC, mpn="UTEST",
+        pins={"1": "3V3", "2": "GND"},
+    )
+
+
+def _cmap():
+    return {
+        "UTEST": ComponentConstraints(
+            mpn="UTEST",
+            pintable=[Pin(number=1, name="VDD"), Pin(number=2, name="GND")],
+            absolute_maximum_ratings=[], rules=[],
+        )
+    }
+
+
+def _cap(ref, farads, net="3V3"):
+    return Component(
+        reference=ref, value="", footprint="C_0603",
+        component_type=ComponentType.CAPACITOR, mpn=ref,
+        pins={"1": net, "2": "GND"},
+        specs=CapacitorSpecs(value_farads=farads, value_formatted="x"),
+    )
+
+
+def test_bulk_only_is_info_ps_esr_001():
+    g = _graph(
+        {"U1": _ic(), "C1": _cap("C1", 10e-6)},
+        {
+            "3V3": (NetType.POWER, [("U1", "1"), ("C1", "1")]),
+            "GND": (NetType.GROUND, [("U1", "2"), ("C1", "2")]),
+        },
+    )
+    findings = check_hf_decoupling_coverage(g, _cmap())
+    assert len(findings) == 1
+    assert findings[0].rule_id == "PS-ESR-001"
+    assert findings[0].status == "INFO"
+
+
+def test_bulk_plus_100n_is_silent():
+    g = _graph(
+        {"U1": _ic(), "C1": _cap("C1", 10e-6), "C2": _cap("C2", 100e-9)},
+        {
+            "3V3": (NetType.POWER, [("U1", "1"), ("C1", "1"), ("C2", "1")]),
+            "GND": (NetType.GROUND, [("U1", "2"), ("C1", "2"), ("C2", "2")]),
+        },
+    )
+    assert check_hf_decoupling_coverage(g, _cmap()) == []
+
+
+def test_unknown_cap_value_is_not_guessed():
+    c = Component(
+        reference="C1", value="", footprint="",
+        component_type=ComponentType.CAPACITOR, mpn="C1",
+        pins={"1": "3V3", "2": "GND"},
+    )
+    g = _graph(
+        {"U1": _ic(), "C1": c},
+        {
+            "3V3": (NetType.POWER, [("U1", "1"), ("C1", "1")]),
+            "GND": (NetType.GROUND, [("U1", "2"), ("C1", "2")]),
+        },
+    )
+    assert check_hf_decoupling_coverage(g, _cmap()) == []