Resolve passives from catalog, BOM value, and Murata LQW18AN without an LLM.

Skip the model (and the credit gate) when LCSC/DigiKey already list C/V/Z, when the BOM value is a single R/C/L/FB token, or when the MPN is an LQW18AN inductor. Ferrite beads keep impedance, not invented henries; value-only specs stay out of the shared library.

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

tests/test_passive_from_value.py

@@ -0,0 +1,88 @@
+import asyncio
+from pathlib import Path
+
+import pytest
+
+from backend.services.passive_from_value import (
+    is_placeholder_value,
+    specs_from_bom_value,
+)
+
+
+def test_capacitor_picofarads():
+    model = specs_from_bom_value("18pF", "18pF", "C")
+    assert model is not None
+    assert model.specs.specs_type == "capacitor"
+    assert abs(model.specs.value_farads - 18e-12) < 1e-18
+
+
+def test_resistor_kilo_and_euro():
+    k = specs_from_bom_value("4.7k", "4.7k", "R")
+    assert k is not None
+    assert abs(k.specs.value_ohms - 4700) < 1e-6
+    euro = specs_from_bom_value("4k7", "4k7", "R")
+    assert euro is not None
+    assert abs(euro.specs.value_ohms - 4700) < 1e-6
+
+
+def test_inductor_uh():
+    model = specs_from_bom_value("10uH", "10uH", "L")
+    assert model is not None
+    assert abs(model.specs.value_henries - 10e-6) < 1e-12
+
+
+def test_ferrite_impedance_at_freq():
+    model = specs_from_bom_value("600R@100MHz", "600R@100MHz", "FB")
+    assert model is not None
+    assert model.specs.component_subtype == "passive.ferrite_bead"
+    assert model.specs.impedance_ohm == 600
+    assert model.specs.value_henries is None
+    assert "100MHz" in model.specs.value_formatted
+
+
+def test_placeholders_skip():
+    for raw in ("DNP", "NC", "JUMPER", "TBD", "-"):
+        assert is_placeholder_value(raw)
+        assert specs_from_bom_value(raw, raw, "R") is None
+
+
+def test_ambiguous_string_returns_none():
+    assert specs_from_bom_value("mystery", "do not stuff", "R") is None
+
+
+def test_resolve_from_value_skips_llm_when_parseable(monkeypatch):
+    from backend.services.extraction import resolve_from_value
+
+    async def boom(*_a, **_k):
+        raise AssertionError("LLM must not run")
+
+    monkeypatch.setattr("backend.services.extraction.call_with_fallback", boom)
+    tax = Path(__file__).resolve().parents[1] / "taxonomy"
+    model = asyncio.run(
+        resolve_from_value(
+            mpn="18pF",
+            value="18pF",
+            ref_prefix="C",
+            taxonomy_dir=tax,
+        )
+    )
+    assert abs(model.specs.value_farads - 18e-12) < 1e-18
+
+
+def test_resolve_from_value_placeholder_no_llm(monkeypatch):
+    from backend.services.extraction import resolve_from_value
+
+    async def boom(*_a, **_k):
+        raise AssertionError("LLM must not run")
+
+    monkeypatch.setattr("backend.services.extraction.call_with_fallback", boom)
+    tax = Path(__file__).resolve().parents[1] / "taxonomy"
+    with pytest.raises(ValueError, match="Placeholder"):
+        asyncio.run(
+            resolve_from_value(
+                mpn="DNP",
+                value="DNP",
+                ref_prefix="R",
+                taxonomy_dir=tax,
+            )
+        )