Tighten PCB findings: actions, stitch gating, real copper.

Fill action on every finding and show it in the report. Stitch/return only
on large HS/power nets. Parse stackup thickness, arcs, and vias from the
board. IC courtyard pad copper is not PE-PLC-004 RULE. Recommended RC/cap
stay REVIEW.

backend/periscopex/parsers_kicad_pcb.py

@@ -5,6 +5,7 @@ No SI/DRC. Schema validation stays complete without this file.
 
 from __future__ import annotations
 
+import re
 from pathlib import Path
 
 from backend.periscopex.models import (
@@ -29,6 +30,24 @@ from backend.periscopex.parsers_kicad import (
 )
 
 
+def _copper_thickness_token(raw: object) -> float | None:
+    """Parse KiCad stackup thickness; units mm/um/mil. Never default 1 oz."""
+    if isinstance(raw, (int, float)) and not isinstance(raw, bool):
+        v = float(raw)
+        return v if v > 0 else None
+    s = str(raw or "").strip().lower().replace(" ", "")
+    m = re.match(r"^([0-9]*\.?[0-9]+)(mm|um|µm|mil)?", s)
+    if not m:
+        return None
+    n = float(m.group(1))
+    unit = m.group(2) or "mm"
+    if unit in {"um", "µm"}:
+        n = n / 1000.0
+    elif unit == "mil":
+        n = n * 0.0254
+    return n if n > 0 else None
+
+
 def _xy(node: object, name: str) -> tuple[float, float]:
     k = _kid(node, name)
     if not k or len(k) < 3:
@@ -128,7 +147,11 @@ def _parse_stackup(tree: object) -> LayoutStackup | None:
         name = str(layer[1]) if len(layer) > 1 and not isinstance(layer[1], list) else ""
         kind = _layer_type(layer)
         thick = _kid(layer, "thickness")
-        height = _fnum(thick[1]) if thick and len(thick) > 1 else None
+        height = None
+        if thick and len(thick) > 1:
+            height = _copper_thickness_token(thick[1])
+            if height is None and len(thick) > 2:
+                height = _copper_thickness_token(f"{thick[1]}{thick[2]}")
         if kind == "copper" or name.endswith(".Cu"):
             if name:
                 copper.append(name)
@@ -147,9 +170,9 @@ def _parse_stackup(tree: object) -> LayoutStackup | None:
                 er=er,
                 height_mm=height,
             ))
-    if len(copper) < 2 or len(dielectrics) != len(copper) - 1:
-        return None
     t = thicknesses[0] if thicknesses else None
+    if not copper and t is None:
+        return None
     return LayoutStackup(
         copper_layers=copper,
         dielectrics=dielectrics,
@@ -291,6 +314,15 @@ def parse_kicad_pcb(path: str | Path) -> LayoutGraph:
                 net=_net_name(node, nets),
             ))
             continue
+        if tag == "arc":
+            segments.append(LayoutSegment(
+                start=_xy(node, "start"),
+                end=_xy(node, "end"),
+                width=_fnum(_val(node, "width") or 0),
+                layer=_val(node, "layer"),
+                net=_net_name(node, nets),
+            ))
+            continue
         if tag == "via":
             drill_el = _kid(node, "drill")
             drill = _fnum(drill_el[1]) if drill_el and len(drill_el) > 1 else None