Fix solver correctness and input-validation issues from code review

- Refuse the uniform contact model when the fills form multiple
  disconnected copper groups that each touch both terminals: the
  prescribed injection split is ill-posed and the grounded system was
  singular, silently returning garbage (e.g. negative gigaohms).
  connected_restrict now reports the component count; a power-balance
  backstop (SolverError) catches any other inconsistent solve.
- Connect via/pad barrels to the nearest fill copper within the pad
  footprint (+1 cell) instead of only the exact center cell, so
  thermal-relief spokes still stitch layers; barrels that reach fill on
  fewer than two layers are warned about. ViaLink gains pad_nm
  (extracted from the padstack, JSON-roundtripped).
- Validate dialog input on OK (layers, current > 0, cell > 0, parseable
  frequency, extra Cu >= 0) with an inline error instead of silently
  substituting defaults; parse_frequency raises on garbage; pipeline
  rejects i_test <= 0; choose_cell_size rejects non-positive overrides.
- Warn when a contact part is dropped by the connectivity restriction;
  floor instead of truncate in cell_of; correct the uniform-model
  summary line; drop an unused variable; refresh plugin.json wording.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

fill_resistance/board_io.py

@@ -355,6 +355,17 @@ def refill(board: Board) -> None:
 
 # --- barrels -----------------------------------------------------------------
 
+def _padstack_pad_nm(item) -> int:
+    """Largest copper pad diameter of a via/pad padstack; 0 if unknown.
+    Used to bound the barrel-to-fill connection search in the solver."""
+    try:
+        sizes = [max(int(l.size.x), int(l.size.y))
+                 for l in item.padstack.copper_layers]
+        return max(sizes) if sizes else 0
+    except Exception:
+        return 0
+
+
 def _padstack_span(padstack, stackup: StackupInfo) -> tuple[int, int]:
     """(z_top, z_bot) of the barrel; falls back to the full stack."""
     try:
@@ -380,7 +391,8 @@ def gather_barrels(board: Board, net_name: str,
         z_top, z_bot = _padstack_span(via.padstack, stackup)
         barrels.append(ViaLink(x=via.position.x, y=via.position.y,
                                drill_nm=drill, z_top_nm=z_top,
-                               z_bot_nm=z_bot, kind="via"))
+                               z_bot_nm=z_bot, kind="via",
+                               pad_nm=_padstack_pad_nm(via)))
     if config.INCLUDE_TH_PADS:
         for pad in board.get_pads():
             if pad.net is None or pad.net.name != net_name:
@@ -390,7 +402,8 @@ def gather_barrels(board: Board, net_name: str,
                 continue
             barrels.append(ViaLink(x=pad.position.x, y=pad.position.y,
                                    drill_nm=drill, z_top_nm=-1,
-                                   z_bot_nm=stackup.z_bot_nm + 1, kind="pad"))
+                                   z_bot_nm=stackup.z_bot_nm + 1, kind="pad",
+                                   pad_nm=_padstack_pad_nm(pad)))
     return barrels
 
 
@@ -411,9 +424,9 @@ def build_problem(board: Board, net: str, layer_names: list[str],
             print(f"note: net {net} has no fill on {name} - layer skipped")
             continue
         if config.COPPER_THICKNESS_UM is not None:
-            t, source = int(config.COPPER_THICKNESS_UM * 1000), "override"
+            t = int(config.COPPER_THICKNESS_UM * 1000)
         else:
-            t, source = stackup.thickness_nm[name], "stackup"
+            t = stackup.thickness_nm[name]
         layers.append(LayerFill(layer_name=name, thickness_nm=t,
                                 z_nm=stackup.z_nm[name], polygons=polys))
     if not layers:

fill_resistance/dialog.py

@@ -96,7 +96,7 @@ class _Dialog(QDialog):
         form.addRow("Extra Cu in openings [µm]:", self.extracu_edit)
 
         buttons = QDialogButtonBox(QDialogButtonBox.Ok | QDialogButtonBox.Cancel)
-        buttons.accepted.connect(self.accept)
+        buttons.accepted.connect(self._try_accept)
         buttons.rejected.connect(self.reject)
 
         lay = QVBoxLayout(self)
@@ -109,13 +109,21 @@ class _Dialog(QDialog):
         note.setWordWrap(True)
         note.setStyleSheet("color: gray; font-size: 10px;")
         lay.addWidget(note)
+        self.error_label = QLabel("")
+        self.error_label.setWordWrap(True)
+        self.error_label.setStyleSheet("color: #b02a2a;")
+        self.error_label.setVisible(False)
+        lay.addWidget(self.error_label)
         lay.addWidget(buttons)
 
+        self._selection: Selection | None = None
+
         self._desired1, self._desired2 = contact1, contact2
         self.net_box.currentTextChanged.connect(self._refresh)
         self._refresh()
 
     def _refresh(self):
+        self.error_label.setVisible(False)
         net = self.net_box.currentText()
         layers = [n for n in self._layer_order
                   if n in self._candidates.get(net, [])]
@@ -144,19 +152,39 @@ class _Dialog(QDialog):
                 out.append(item.text())
         return out
 
-    def selection(self) -> Selection | None:
+    def _build_selection(self) -> Selection:
+        """Parse and validate every field; raises ValueError with a
+        user-readable message instead of silently substituting defaults
+        (a typo silently becoming 1 A / DC would mislabel the result)."""
         layers = self.checked_layers()
         if not layers:
-            return None
+            raise ValueError("Check at least one layer.")
+
+        def number(edit: QLineEdit, name: str) -> float:
             try:
-            current = float(self.current_edit.text().replace(",", "."))
+                return float(edit.text().strip().replace(",", "."))
-        except ValueError:
-            current = config.TEST_CURRENT_A
-        cell_text = self.cell_edit.text().strip()
-        try:
-            cell = float(cell_text.replace(",", ".")) if cell_text else None
             except ValueError:
+                raise ValueError(f"{name}: '{edit.text()}' is not a number.")
+
+        current = number(self.current_edit, "Test current")
+        if current <= 0:
+            raise ValueError("Test current must be > 0 A.")
         cell = None
+        if self.cell_edit.text().strip():
+            cell = number(self.cell_edit, "Cell size")
+            if cell <= 0:
+                raise ValueError("Cell size must be > 0 µm.")
+        try:
+            freq = skin.parse_frequency(self.freq_edit.text())
+        except ValueError:
+            raise ValueError(
+                f"Frequency: cannot parse '{self.freq_edit.text()}' "
+                f"(examples: 0, 142k, 1.5M).")
+        extra_cu = 0.0
+        if self.extracu_edit.isEnabled():
+            extra_cu = number(self.extracu_edit, "Extra Cu")
+            if extra_cu < 0:
+                raise ValueError("Extra Cu must be ≥ 0 µm.")
 
         def contact(box: QComboBox) -> str:
             t = box.currentText()
@@ -164,18 +192,23 @@ class _Dialog(QDialog):
                 return "auto"
             return "all" if t == ALL_LAYERS else t
 
-        try:
-            extra_cu = float(self.extracu_edit.text().replace(",", "."))
-        except ValueError:
-            extra_cu = 0.0
         return Selection(net=self.net_box.currentText(), layers=layers,
                          contact1=contact(self.contact1_box),
                          contact2=contact(self.contact2_box),
                          current_a=current, cell_um=cell,
-                         freq_hz=skin.parse_frequency(self.freq_edit.text()),
+                         freq_hz=freq,
                          contact_model=self.model_box.currentData(),
                          include_buildup=self.buildup_check.isChecked(),
-                         extra_cu_um=max(0.0, extra_cu))
+                         extra_cu_um=extra_cu)
+
+    def _try_accept(self) -> None:
+        try:
+            self._selection = self._build_selection()
+        except ValueError as e:
+            self.error_label.setText(str(e))
+            self.error_label.setVisible(True)
+            return
+        self.accept()
 
 
 def ask(candidates: dict[str, list[str]], layer_order: list[str],
@@ -190,4 +223,4 @@ def ask(candidates: dict[str, list[str]], layer_order: list[str],
     dlg.activateWindow()
     if dlg.exec() != QDialog.Accepted:
         return None
-    return dlg.selection()
+    return dlg._selection

fill_resistance/errors.py

@@ -32,3 +32,7 @@ class ConnectivityError(UserFacingError):
 
 class GridSizeError(UserFacingError):
     pass
+
+
+class SolverError(UserFacingError):
+    pass

fill_resistance/geometry.py

@@ -87,6 +87,7 @@ class ViaLink:
     z_top_nm: int
     z_bot_nm: int
     kind: str = "via"                         # "via" | "pad"
+    pad_nm: int = 0                           # pad/annular diameter; 0 = unknown
 
     def spans(self, z_nm: int) -> bool:
         return self.z_top_nm - 1 <= z_nm <= self.z_bot_nm + 1
@@ -287,7 +288,8 @@ def problem_from_json(d: dict) -> Problem:
         vias=[
             ViaLink(x=int(vd["x"]), y=int(vd["y"]), drill_nm=int(vd["drill_nm"]),
                     z_top_nm=int(vd["z_top_nm"]), z_bot_nm=int(vd["z_bot_nm"]),
-                    kind=vd.get("kind", "via"))
+                    kind=vd.get("kind", "via"),
+                    pad_nm=int(vd.get("pad_nm", 0)))
             for vd in d["vias"]
         ],
         electrodes1=(

fill_resistance/pipeline.py

@@ -5,6 +5,7 @@ from __future__ import annotations
 from pathlib import Path
 
 from . import config, plots, raster, report, solver
+from .errors import UserFacingError
 from .geometry import Problem
 from .solver import Result
 
@@ -14,6 +15,8 @@ def run(problem: Problem, outdir: Path | None, show: bool = True,
         contact_model: str | None = None) -> Result:
     if i_test is None:
         i_test = config.TEST_CURRENT_A
+    if i_test <= 0:
+        raise UserFacingError(f"Test current must be > 0 A (got {i_test:g}).")
     h = raster.choose_cell_size(problem.copper_bbox(), len(problem.layers))
     print(f"rasterizing {len(problem.layers)} layer(s) at cell size "
           f"{h / 1000:.1f} um ...")

fill_resistance/raster.py

@@ -54,8 +54,8 @@ class RasterStack:
     def cell_of(self, x_nm: float, y_nm: float) -> tuple[int, int] | None:
         """(i, j) of the cell containing the point, or None if outside."""
         ny, nx = self.shape2d
-        j = int((x_nm - self.x0_nm) / self.h_nm)
+        j = math.floor((x_nm - self.x0_nm) / self.h_nm)
-        i = int((y_nm - self.y0_nm) / self.h_nm)
+        i = math.floor((y_nm - self.y0_nm) / self.h_nm)
         if 0 <= i < ny and 0 <= j < nx:
             return i, j
         return None
@@ -81,6 +81,11 @@ def choose_cell_size(bbox_nm: tuple[int, int, int, int], nlayers: int) -> float:
         raise GridSizeError("Copper geometry has a degenerate bounding box.")
 
     if config.CELL_UM_OVERRIDE is not None:
+        if config.CELL_UM_OVERRIDE <= 0:
+            raise GridSizeError(
+                f"Cell size must be positive "
+                f"(got {config.CELL_UM_OVERRIDE:g} um)."
+            )
         h = config.CELL_UM_OVERRIDE * 1000.0
     else:
         h = math.sqrt(w * ht * nlayers / config.TARGET_CELLS)

fill_resistance/report.py

@@ -102,8 +102,11 @@ def write_summary(outdir: Path, problem: Problem, stack: RasterStack,
         f"solver:            {info.method}"
         + (f", {info.iterations} iters, residual {info.residual:.2e}"
            if info.iterations is not None else ""),
-        f"I1/I2 @ 1V:        {result.I1_a:.9g} / {result.I2_a:.9g} A "
+        (f"I1/I2 @ 1V:        {result.I1_a:.9g} / {result.I2_a:.9g} A "
-        f"(mismatch {result.mismatch_rel:.2e})",
+         f"(mismatch {result.mismatch_rel:.2e})"
+         if result.contact_model == "equipotential" else
+         f"solve residual:    {result.mismatch_rel:.2e} "
+         f"(KCL, prescribed injection)"),
         f"timings [s]:       "
         f"{', '.join(f'{k}={v:.2f}' for k, v in result.timings.items())}",
         "",

fill_resistance/skin.py

@@ -59,7 +59,9 @@ def resistance_factor(thickness_m: float, freq_hz: float,
 
 
 def parse_frequency(text: str) -> float:
-    """'0', '100k', '1.5M', '142500' -> Hz. Empty/invalid -> 0 (DC)."""
+    """'0', '100k', '1.5M', '142500' -> Hz; empty -> 0 (DC).
+    Raises ValueError on unparseable or negative input (a typo silently
+    becoming DC would mislabel the result)."""
     t = text.strip().lower().replace(",", ".").removesuffix("hz").strip()
     if not t:
         return 0.0
@@ -72,7 +74,7 @@ def parse_frequency(text: str) -> float:
         mult, t = 1e3, t[:-1]
     elif t.endswith("g"):
         mult, t = 1e9, t[:-1]
-    try:
+    value = float(t) * mult          # ValueError on garbage
-        return max(0.0, float(t) * mult)
+    if value < 0:
-    except ValueError:
+        raise ValueError(f"negative frequency: {text!r}")
-        return 0.0
+    return value

fill_resistance/solver.py

@@ -2,10 +2,12 @@
 
 Each included copper layer is a 2D 5-point sheet with per-layer face
 conductance sigma_s = t/rho [S] (square cells: independent of h); via and
-plated-through-pad barrels add vertical conductances between vertically
+plated-through-pad barrels add vertical conductances between the layers
-aligned cells of the layers they span AND reach copper on. A barrel
+they span AND reach copper on. Per layer the barrel attaches to the cell
-passing an antipad still bridges the layers above/below it with the full
+under it, or to the nearest copper cell within the pad footprint (+1
-barrel length. At freq > 0 the per-layer sheet conductances and the
+cell) - fills joined by thermal-relief spokes still connect. A barrel
+passing a (wider) antipad still bridges the layers above/below it with
+the full barrel length. At freq > 0 the per-layer sheet conductances and the
 barrel walls get the 1D skin-effect correction (see skin.py; AC results
 are a rigorous lower bound - lateral redistribution is not modeled).
 
@@ -44,7 +46,7 @@ from scipy.sparse import csgraph
 from scipy.sparse import linalg as sla
 
 from . import config, skin
-from .errors import ConnectivityError, ElectrodeError
+from .errors import ConnectivityError, ElectrodeError, SolverError
 from .geometry import Problem
 from .raster import RasterStack, electrodes_touch
 
@@ -63,6 +65,8 @@ class Edges:
     b: np.ndarray
     w: np.ndarray                 # conductance [S]
     via_index: np.ndarray         # int32; -1 = in-plane edge
+    dead_barrels: int = 0         # barrels spanning >=2 layers that found
+                                  # fill copper on fewer than 2 of them
 
 
 @dataclass
@@ -159,35 +163,63 @@ def build_edges(stack: RasterStack, problem: Problem, sigmas: list[float],
                 ww.append(2.0 * s_a * s_b / (s_a + s_b))
             vv.append(np.full(len(a), -1, dtype=np.int32))
 
+    h = stack.h_nm
+    dead_barrels = 0
     for vi, via in enumerate(problem.vias):
         cell = stack.cell_of(via.x, via.y)
         if cell is None:
             continue
         i, j = cell
-        present = [li for li, layer in enumerate(problem.layers)
+        span = [li for li, layer in enumerate(problem.layers)
-                   if via.spans(layer.z_nm) and stack.masks[li, i, j]]
+                if via.spans(layer.z_nm)]
-        for la, lb in zip(present[:-1], present[1:]):
+        # Connection cell per layer: the cell under the barrel, or the
+        # nearest copper cell whose center lies within the pad footprint
+        # (+1 cell of rasterization slop) - fills joined to the barrel by
+        # thermal-relief spokes still connect, wider antipads do not (the
+        # barrel then bridges the layers above/below as before).
+        r_nm = max(via.pad_nm, via.drill_nm + 300_000) / 2.0 + h
+        win = int(r_nm // h) + 1
+        i0, i1 = max(0, i - win), min(ny, i + win + 1)
+        j0, j1 = max(0, j - win), min(nx, j + win + 1)
+        xs = stack.x0_nm + (np.arange(j0, j1) + 0.5) * h - via.x
+        ys = stack.y0_nm + (np.arange(i0, i1) + 0.5) * h - via.y
+        d2 = ys[:, None] ** 2 + xs[None, :] ** 2
+        d2 = np.where(d2 <= r_nm * r_nm, d2, np.inf)
+        present = []                            # (layer, i, j) per layer
+        for li in span:
+            if stack.masks[li, i, j]:
+                present.append((li, i, j))
+                continue
+            dc = np.where(stack.masks[li, i0:i1, j0:j1], d2, np.inf)
+            ci, cj = np.unravel_index(int(np.argmin(dc)), dc.shape)
+            if np.isfinite(dc[ci, cj]):
+                present.append((li, i0 + ci, j0 + cj))
+        if len(span) >= 2 and len(present) < 2:
+            dead_barrels += 1
+        for (la, ia, ja), (lb, ib, jb) in zip(present[:-1], present[1:]):
             length = problem.layers[lb].z_nm - problem.layers[la].z_nm
             if length <= 0:
                 continue
             r = via.barrel_resistance(length, problem.rho_ohm_m,
                                       problem.plating_nm) * via_factor
-            aa.append(np.array([la * plane + i * nx + j], dtype=np.int64))
+            aa.append(np.array([la * plane + ia * nx + ja], dtype=np.int64))
-            bb.append(np.array([lb * plane + i * nx + j], dtype=np.int64))
+            bb.append(np.array([lb * plane + ib * nx + jb], dtype=np.int64))
             ww.append(np.array([1.0 / r]))
             vv.append(np.array([vi], dtype=np.int32))
 
     if not aa:
         raise ConnectivityError("No copper found on the selected layers.")
     return Edges(a=np.concatenate(aa), b=np.concatenate(bb),
-                 w=np.concatenate(ww), via_index=np.concatenate(vv))
+                 w=np.concatenate(ww), via_index=np.concatenate(vv),
+                 dead_barrels=dead_barrels)
 
 
 def connected_restrict(stack: RasterStack, e1: np.ndarray, e2: np.ndarray,
-                       edges: Edges) -> bool:
+                       edges: Edges) -> tuple[bool, int]:
     """Keep only components (through-plane AND through-via) touching both
-    terminals. Mutates stack.masks / e1 / e2. Returns True if anything
+    terminals. Mutates stack.masks / e1 / e2. Returns (changed,
-    was dropped (caller must rebuild edges)."""
+    n_components): whether anything was dropped (caller must rebuild
+    edges) and how many disjoint copper groups survive."""
     n = stack.masks.size
     graph = sparse.coo_matrix(
         (np.ones(len(edges.a)), (edges.a, edges.b)), shape=(n, n))
@@ -205,7 +237,7 @@ def connected_restrict(stack: RasterStack, e1: np.ndarray, e2: np.ndarray,
     stack.masks &= keep
     e1 &= keep
     e2 &= keep
-    return changed
+    return changed, len(common)
 
 
 def _assemble(state: np.ndarray, edges: Edges, rhs_extra: np.ndarray | None):
@@ -280,7 +312,7 @@ def solve_system(A: sparse.csr_matrix, b: np.ndarray) -> tuple[np.ndarray, Solve
         x, code = sla.cg(A, b, M=M, tol=config.CG_TOL,
                          maxiter=config.CG_MAXITER, callback=count)
     if code != 0:
-        raise RuntimeError(
+        raise SolverError(
             f"CG did not converge in {config.CG_MAXITER} iterations "
             f"(code {code}). Try a coarser grid or raise CG_MAXITER."
         )
@@ -460,12 +492,31 @@ def run_solve(problem: Problem, stack: RasterStack, e1: np.ndarray,
 
     t0 = time.perf_counter()
     edges = build_edges(stack, problem, sigmas, via_factor, sigma_buildup)
-    if connected_restrict(stack, e1, e2, edges):
+    changed, n_groups = connected_restrict(stack, e1, e2, edges)
+    if changed:
         edges = build_edges(stack, problem, sigmas, via_factor, sigma_buildup)
+    if edges.dead_barrels:
+        print(f"warning: {edges.dead_barrels} via/pad barrel(s) found fill "
+              f"copper on fewer than 2 layers and carry no current (pad "
+              f"copper is not modeled; a finer grid may pick up thermal "
+              f"spokes)")
+    if n_groups > 1 and contact_model != "equipotential":
+        raise ConnectivityError(
+            f"The selected fills form {n_groups} disconnected copper groups "
+            f"that each touch both terminals. The uniform-injection contact "
+            f"model cannot determine the current split between disconnected "
+            f"sheets - switch to the equipotential contact model (bonded "
+            f"lug), or include the layers/vias that join them."
+        )
     if stack.buildup is not None:
         stack.buildup &= stack.masks
-    for _, m in (parts1 or []) + (parts2 or []):
+    for label, m in (parts1 or []) + (parts2 or []):
+        had = bool(m.any())
         m &= stack.masks                     # follow the component restriction
+        if had and not m.any():
+            print(f"warning: contact part '{label}' only touches copper "
+                  f"that is not connected to both terminals - it carries "
+                  f"no current")
     timings["edges_s"] = time.perf_counter() - t0
 
     t0 = time.perf_counter()
@@ -494,6 +545,13 @@ def run_solve(problem: Problem, stack: RasterStack, e1: np.ndarray,
     P_vias = float(Pe[~inplane].sum())
     P_total = i_test ** 2 * R
     balance = abs((sum(P_layers) + P_vias) - P_total) / max(P_total, 1e-300)
+    if not np.isfinite(balance) or balance > 1e-3:
+        raise SolverError(
+            f"Inconsistent solve: R = {R:.6g} ohm with power-balance error "
+            f"{balance:.2e} (sum of edge powers vs I^2*R). The result is "
+            f"not trustworthy - try the equipotential contact model or a "
+            f"different grid size."
+        )
 
     # via reports: max segment current + total power per via
     Ie = edges.w * (Vflat[edges.a] - Vflat[edges.b])   # amps at unit drive

fill_resistance/standalone.py

@@ -16,6 +16,7 @@ from pathlib import Path
 from . import config, pipeline
 from .errors import UserFacingError
 from .geometry import load_problem
+from .skin import parse_frequency
 
 
 def main(argv=None) -> int:
@@ -23,7 +24,7 @@ def main(argv=None) -> int:
     ap.add_argument("dump", type=Path, help="geometry_dump.json from a plugin run")
     ap.add_argument("--current", type=float, default=None,
                     help="test current [A] (default: config TEST_CURRENT_A)")
-    ap.add_argument("--freq", type=str, default="0",
+    ap.add_argument("--freq", type=parse_frequency, default=0.0,
                     help="frequency, e.g. 142k or 1.5M (default: DC). "
                          "AC results are a lower bound (skin per foil only)")
     ap.add_argument("--cell-um", type=float, default=None,
@@ -64,11 +65,10 @@ def main(argv=None) -> int:
                   file=sys.stderr)
             return 1
 
-    from .skin import parse_frequency
     outdir = args.out if args.out is not None else args.dump.parent
     try:
         pipeline.run(problem, outdir, show=not args.no_show,
-                     i_test=args.current, freq_hz=parse_frequency(args.freq),
+                     i_test=args.current, freq_hz=args.freq,
                      contact_model=args.contact_model)
     except UserFacingError as e:
         print(f"ERROR: {e}", file=sys.stderr)

plugin.json

@@ -2,7 +2,7 @@
     "$schema": "https://go.kicad.org/api/schemas/v1",
     "identifier": "th.co.b4l.fill-resistance",
     "name": "Fill Resistance",
-    "description": "DC resistance of a copper zone fill between two rectangle electrodes",
+    "description": "DC/AC resistance of copper zone fills between two contacts (marker rectangles or pads), single- or multi-layer with via coupling",
     "runtime": {
         "type": "python"
     },
@@ -10,7 +10,7 @@
         {
             "identifier": "fill-resistance-run",
             "name": "Fill Resistance",
-            "description": "Select two rectangles marking the contact areas, then run to compute the fill resistance between them",
+            "description": "Mark the contacts (rectangles on the User.1/User.2 marker layers and/or selected pads), then run to compute the fill resistance between them",
             "entrypoint": "fill_res_action.py",
             "show-button": true,
             "scopes": ["pcb"],

tests/test_contacts.py

@@ -3,9 +3,10 @@ import numpy as np
 import pytest
 
 from fill_resistance import raster, solver
-from fill_resistance.errors import ElectrodeError
+from fill_resistance.errors import ConnectivityError, ElectrodeError
 from fill_resistance.geometry import Electrode
-from tests.util import NM, make_problem, rect_mm, sigma_s, strip_problem
+from tests.util import (NM, make_multilayer, make_problem, rect_mm, sigma_s,
+                        strip_problem)
 
 
 def _solve(problem, h_mm, model, i_test=1.0):
@@ -161,6 +162,22 @@ def test_injection_area_partition_first_wins():
     assert total == pytest.approx(1.0, rel=1e-12)
 
 
+def test_uniform_multicomponent_raises():
+    """Two disconnected sheets that each touch both terminals: the
+    uniform model would build a singular system (one ground cell, pure-
+    Neumann second component) and previously returned garbage silently
+    (e.g. negative gigaohms). It must refuse; equipotential handles it."""
+    strip1 = [(0, 0), (10, 0), (10, 1), (0, 1)]
+    strip2 = [(0, 0), (10, 0), (10, 2), (0, 2)]   # asymmetric shares
+    p = make_multilayer([[(strip1, [])], [(strip2, [])]],
+                        (0, 0, 1, 2), (9, 0, 10, 1))  # contact 'all', no vias
+    with pytest.raises(ConnectivityError, match="disconnected"):
+        _solve(p, 1.0, "uniform")
+    res, _ = _solve(p, 1.0, "equipotential")
+    assert np.isfinite(res.R_ohm) and res.R_ohm > 0
+    assert res.power_balance_rel < 1e-9
+
+
 def test_touching_ok_uniform_error_equipotential():
     p = make_problem([([(0, 0), (10, 0), (10, 10), (0, 10)], [])],
                      rect1_mm=(0, 0, 5, 10), rect2_mm=(5, 0, 10, 10))

tests/test_geometry.py

@@ -51,6 +51,7 @@ def test_problem_json_roundtrip_v2(tmp_path):
          [([(0, 0), (10, 0), (10, 1), (0, 1)], [])]],
         rect1_mm=(0, 0, 1, 1), rect2_mm=(9, 0, 10, 1),
         contact1="L0", contact2="L1", vias_mm=[(5.5, 0.5)])
+    p.vias[0].pad_nm = 600_000
     f = tmp_path / "dump.json"
     save_problem(p, f)
     q = load_problem(f)
@@ -58,6 +59,7 @@ def test_problem_json_roundtrip_v2(tmp_path):
     assert q.electrodes1[0].contact == "L0"
     assert q.electrodes2[0].contact == "L1"
     assert len(q.vias) == 1 and q.vias[0].drill_nm == p.vias[0].drill_nm
+    assert q.vias[0].pad_nm == 600_000
     assert q.plating_nm == p.plating_nm
     assert np.array_equal(q.layers[0].polygons[0].outline,
                           p.layers[0].polygons[0].outline)

tests/test_multilayer.py

@@ -74,9 +74,10 @@ def test_parallel_vias_halve_barrel_resistance():
 
 
 def test_antipad_bridging():
-    """3 layers; the middle layer has an antipad hole at the via cell, so
+    """3 layers; the middle layer has an antipad hole at the via, WIDER
-    the barrel bridges L0 -> L2 directly with DOUBLE the length."""
+    than the barrel connection search (pad footprint + 1 cell), so the
-    mid_with_hole = [(STRIP, [[(5, 0), (6, 0), (6, 1), (5, 1)]])]
+    barrel bridges L0 -> L2 directly with DOUBLE the length."""
+    mid_with_hole = [(STRIP, [[(4, 0), (7, 0), (7, 1), (4, 1)]])]
     p = make_multilayer(
         [[(STRIP, [])], mid_with_hole, [(STRIP, [])]],
         rect1_mm=(0, 0, 1, 1), rect2_mm=(9, 0, 10, 1),
@@ -88,6 +89,43 @@ def test_antipad_bridging():
     assert res.R_ohm == pytest.approx(r_exact, rel=1e-9)
 
 
+def test_thermal_gap_via_connects_to_nearby_copper():
+    """The cell under the via is not copper (thermal-relief knockout),
+    but fill copper within the pad footprint (+1 cell) still reaches the
+    barrel: the link lands on the nearest copper cell instead of being
+    silently dropped."""
+    top_with_gap = [(STRIP, [[(5, 0), (7, 0), (7, 1), (5, 1)]])]
+    p = make_multilayer(
+        [top_with_gap, [(STRIP, [])]],
+        rect1_mm=(0, 0, 1, 1), rect2_mm=(9, 0, 10, 1),
+        contact1="L0", contact2="L1",
+        vias_mm=[(5.5, 0.5)], gap_mm=1.0)
+    res, _ = _solve(p, 1.0)
+    sig = sigma_s()
+    # L0 attaches at col 4 (nearest copper, 1.0 mm from the barrel),
+    # L1 at col 5: 4 faces on L0, the barrel, 4 faces on L1 - exact
+    r_exact = (4 + 4) / sig + _r_via(1.0)
+    assert res.R_ohm == pytest.approx(r_exact, rel=1e-9)
+    assert len(res.via_reports) == 1
+    assert res.via_reports[0].current_a == pytest.approx(1.0, rel=1e-9)
+
+
+def test_dead_barrel_is_warned(capsys):
+    """A via isolated from the fill by an antipad wider than the search
+    radius on all but one layer carries nothing and is reported."""
+    bot_with_hole = [(STRIP, [[(3, 0), (8, 0), (8, 1), (3, 1)]])]
+    p = make_multilayer(
+        [[(STRIP, [])], bot_with_hole],
+        rect1_mm=(0, 0, 1, 1), rect2_mm=(9, 0, 10, 1),
+        contact1="L0", contact2="L0",
+        vias_mm=[(5.5, 0.5)], gap_mm=1.0)
+    res, _ = _solve(p, 1.0)
+    sig = sigma_s()
+    assert res.R_ohm == pytest.approx(9 / sig, rel=1e-9)   # L0 alone
+    assert res.via_reports == []
+    assert "carry no current" in capsys.readouterr().out
+
+
 def test_via_short_between_electrodes_raises():
     """Both electrodes over the SAME cell on different layers with a via
     there = direct short, no free copper -> error."""

tests/test_raster.py

@@ -90,6 +90,14 @@ def test_hard_max_cells_guard(monkeypatch):
         raster.choose_cell_size(p.copper_bbox(), len(p.layers))
 
 
+def test_cell_override_nonpositive_raises(monkeypatch):
+    p = strip_problem()
+    for bad in (0.0, -50.0):
+        monkeypatch.setattr(config, "CELL_UM_OVERRIDE", bad)
+        with pytest.raises(GridSizeError, match="positive"):
+            raster.choose_cell_size(p.copper_bbox(), len(p.layers))
+
+
 def test_auto_cell_size_hits_target():
     # large plane: unclamped regime, cell count tracks TARGET_CELLS
     p = strip_problem(length=200, width=100, e_len=5)

tests/test_skin.py

@@ -58,7 +58,10 @@ def test_parse_frequency():
     assert skin.parse_frequency("2meg") == 2_000_000.0
     assert skin.parse_frequency("100000") == 100_000.0
     assert skin.parse_frequency("100 kHz") == 100_000.0
-    assert skin.parse_frequency("junk") == 0.0
+    with pytest.raises(ValueError):
+        skin.parse_frequency("junk")      # must not silently become DC
+    with pytest.raises(ValueError):
+        skin.parse_frequency("-5k")
 
 
 def test_single_layer_ac_scales_exactly():

tests/test_solver.py

@@ -112,6 +112,17 @@ def test_test_current_scaling():
     assert r10.P_total == pytest.approx(100 * r1.P_total, rel=1e-9)
 
 
+def test_nonpositive_test_current_rejected():
+    """i_test <= 0 would divide by zero in the percentage reporting;
+    it must be rejected up front with a clean user-facing message."""
+    from fill_resistance import pipeline
+    from fill_resistance.errors import UserFacingError
+    p = strip_problem()
+    for bad in (0.0, -1.0):
+        with pytest.raises(UserFacingError, match="Test current"):
+            pipeline.run(p, None, show=False, i_test=bad)
+
+
 def test_power_identity():
     """Sum of edge powers equals I^2 R exactly for the direct solve."""
     p = make_problem(