Integrate ImpedenceFinder closed-form Z0 into the project Impedance tab.

Use the vendored Hammerstad-Jensen/Cohn engine for microstrip, stripline, and coupled-diff advice. Skip OpenEMS/pcbnew and refuse CPWG rather than inventing a number.

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

frontend/src/lib/api.ts

@@ -10,6 +10,9 @@ import type {
   CreditSnapshot,
   DesignGraph,
   DeratingRow,
+  ImpedanceKind,
+  ImpedanceStackupResult,
+  ImpedanceTraceResult,
   EdifSubDesign,
   FindingComment,
   LcscPayload,
@@ -582,6 +585,28 @@ export async function fetchDerating(
   return res.json();
 }
 
+export async function computeImpedance(body: {
+  mode: "trace" | "stackup";
+  kind?: ImpedanceKind;
+  h: number;
+  er: number;
+  t: number;
+  w?: number | null;
+  s?: number | null;
+  target_z?: number | null;
+}): Promise<ImpedanceTraceResult | ImpedanceStackupResult> {
+  const res = await authFetch(`${BASE}/api/impedance`, {
+    method: "POST",
+    headers: { "Content-Type": "application/json" },
+    body: JSON.stringify(body),
+  });
+  if (!res.ok) {
+    const detail = await res.json().catch(() => ({ detail: res.statusText }));
+    throw new Error(typeof detail.detail === "string" ? detail.detail : "Impedance compute failed");
+  }
+  return res.json();
+}
+
 export async function fetchReport(
   projectId: string,
 ): Promise<ValidationReport> {