Check ImpedenceFinder against datasheet SI rules, not a dump table.

Each layout_rules SI requirement (diff/SE Z, skew, max length, spacing,
ref plane, vias, layer, return, series R) is one PASS/FAIL/MARGIN finding
with FACT and REQUIREMENT. USB/HDMI/PCIe/ETH/LVDS/DDR only; I2C GPIO CC
and analog REGN are skipped. No invented 90 Ω.

backend/services/pcb_pipeline.py

@@ -183,15 +183,19 @@ async def run_pcb_pipeline(
 
             _step(project_id, "inventory", "running")
             z0_by_net: dict[str, float] = {}
+            zrep: dict = {"nets": [], "skipped": None}
             try:
                 from backend.periscopex.impedance_traces import analyze_where_needed
 
                 zrep = analyze_where_needed(layout, graph)
+                zpath = ws.local_path("impedance_nets.json")
+                zpath.write_text(json.dumps(zrep, indent=2) + "\n")
+                ws._upload_file("impedance_nets.json")
                 for row in zrep.get("nets") or []:
                     if not isinstance(row, dict) or row.get("error"):
                         continue
                     name = str(row.get("net_name") or row.get("name") or "")
-                    z = row.get("z0_ohm") or row.get("mean_z0") or row.get("z0")
+                    z = row.get("z0_avg_ohms") or row.get("z0_ohm") or row.get("mean_z0") or row.get("z0")
                     if name and isinstance(z, (int, float)):
                         z0_by_net[name] = float(z)
             except Exception:
@@ -215,7 +219,7 @@ async def run_pcb_pipeline(
                 return
 
             _step(project_id, "checks", "running")
-            findings = run_pcb_checks(graph, cmap, layout, plan)
+            findings = run_pcb_checks(graph, cmap, layout, plan, zrep)
             _step(
                 project_id, "checks", "complete",
                 f"{len(findings)} deterministic findings",