verify: model-driven pin checks (contention / undriven / NC-wired)

New bsdl_check.{hpp,cpp}: check_pin_specs(System*) walks the nets and uses
each pin's PinSpec direction/function to flag DriveContention (>=2 push-pull
output drivers), UndrivenNet (a multi-pin net with input(s) but no driver),
and NcWired (a no-connect pin wired onto a multi-pin net). Added as a pass in
`verify`; AnomalyKind extended accordingly. Nets with no direction data are
skipped, so un-modelled parts produce no noise. Covered by test_bsdl_check.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

tests/test_bsdl_check.cpp

@@ -0,0 +1,92 @@
+#include <doctest/doctest.h>
+
+#include "system/analysis.hpp"
+#include "system/bsdl_check.hpp"
+#include "system/modules.hpp"
+#include "system/parts.hpp"
+#include "system/pin_spec.hpp"
+#include "system/pins.hpp"
+#include "system/signals.hpp"
+#include "system/system.hpp"
+
+#include <algorithm>
+#include <vector>
+
+namespace {
+
+Pin *mkpin(Part *part, const char *name, PinDirection d, PinFunction f)
+{
+    Pin *p = new Pin(name);
+    p->spec.direction = d;
+    p->spec.function = f;
+    p->spec.source = SpecSource::Bsdl;
+    part->add(p);
+    return p;
+}
+
+void wire(Module *m, const char *signame, std::vector<Pin *> pins)
+{
+    Signal *s = m->signals->merge(signame);
+    for (Pin *p : pins) {
+        s->add(p);
+        p->connect(s);
+    }
+}
+
+int count_kind(const std::vector<Anomaly> &v, AnomalyKind k)
+{
+    return (int)std::count_if(v.begin(), v.end(),
+                              [&](const Anomaly &a) { return a.kind == k; });
+}
+
+}  // namespace
+
+TEST_CASE("check_pin_specs flags contention, undriven nets and NC-wired pins") {
+    System sys;
+    Module *m = sys.modules()->merge("M");
+    Part *u1 = new Part("U1");
+    Part *u2 = new Part("U2");
+    m->add(u1);
+    m->add(u2);
+
+    // Two push-pull outputs on one net → contention.
+    wire(m, "NET_CONT", {mkpin(u1, "O1", PinDirection::Out, PinFunction::Signal),
+                         mkpin(u2, "O2", PinDirection::Out, PinFunction::Signal)});
+
+    // Two inputs, no driver → undriven.
+    wire(m, "NET_UNDR", {mkpin(u1, "I1", PinDirection::In, PinFunction::Signal),
+                         mkpin(u2, "I2", PinDirection::In, PinFunction::Signal)});
+
+    // A no-connect pin wired to a driver → nc-wired (and not undriven: the
+    // NC pin is Power-direction here, so the net has a driver).
+    wire(m, "NET_NC", {mkpin(u1, "NC1", PinDirection::Power, PinFunction::NoConnect),
+                       mkpin(u2, "D1", PinDirection::Out, PinFunction::Signal)});
+
+    // Healthy: one driver + one input → no anomaly.
+    wire(m, "NET_OK", {mkpin(u1, "OD", PinDirection::Out, PinFunction::Signal),
+                       mkpin(u2, "ID", PinDirection::In, PinFunction::Signal)});
+
+    auto anoms = check_pin_specs(&sys);
+    CHECK(count_kind(anoms, AnomalyKind::DriveContention) == 1);
+    CHECK(count_kind(anoms, AnomalyKind::UndrivenNet) == 1);
+    CHECK(count_kind(anoms, AnomalyKind::NcWired) == 1);
+}
+
+TEST_CASE("check_pin_specs stays silent on un-modelled nets") {
+    System sys;
+    Module *m = sys.modules()->merge("M");
+    Part *u1 = new Part("U1");
+    Part *u2 = new Part("U2");
+    m->add(u1);
+    m->add(u2);
+
+    // No specs set (direction Unknown / function Unknown) → no findings.
+    Pin *a = new Pin("A");
+    Pin *b = new Pin("B");
+    u1->add(a);
+    u2->add(b);
+    wire(m, "NET", {a, b});
+
+    auto anoms = check_pin_specs(&sys);
+    CHECK(anoms.empty());
+}