feat(sim): P2 wiring ERC slice 2 — VCC-to-GND short + shorted-out parts

- Power short (blocking error): a wire joining a VCC-type pin directly to a
  GND-type pin shorts the supply to ground. The current-based short-circuit
  rule only inspects battery/signal-generator/power-supply sources, so it
  misses a board-rail-to-GND short with no such source -> name it structurally.
- Shorted-out part (warning): a 2-terminal part with both terminals on the same
  node has no effect on the circuit.

Both graph-based, run before the solve. Zero false positives across the 69
gallery examples; gallery pre-flight tests still pass (no spurious blocking).

frontend/src/__tests__/circuit-verifier.test.ts

@@ -426,6 +426,41 @@ describe('verifyCircuit — wiring ERC (bad connections)', () => {
       expect(mc, JSON.stringify(result.warnings)).toBeDefined();
     },
   );
+
+  it(
+    'errors when a VCC pin is wired directly to a GND pin',
+    { timeout: 30_000 },
+    async () => {
+      const input: BuildNetlistInput = {
+        components: [{ id: 'o1', metadataId: 'ssd1306', properties: {} }],
+        wires: [w('w1', ['o1', '3V3'], ['o1', 'GND'])], // VCC tied straight to GND
+        boards: [],
+        analysis: { kind: 'op' },
+      };
+      const result = await verifyCircuit(input);
+      const codes = result.errors.map((e) => e.code);
+      expect(codes, JSON.stringify(result.errors)).toContain('power-short');
+    },
+  );
+
+  it(
+    'warns when a part has both terminals on the same node (shorted out)',
+    { timeout: 30_000 },
+    async () => {
+      const input: BuildNetlistInput = {
+        components: [pwr('src', 5), res('r1', '1k')],
+        wires: [
+          w('w1', ['src', 'SIG'], ['r1', '1']),
+          w('w2', ['src', 'SIG'], ['r1', '2']), // both terminals on the SIG net
+        ],
+        boards: [],
+        analysis: { kind: 'op' },
+      };
+      const result = await verifyCircuit(input);
+      const sc = result.warnings.find((x) => x.code === 'shorted-component' && x.componentId === 'r1');
+      expect(sc, JSON.stringify(result.warnings)).toBeDefined();
+    },
+  );
 });
 
 // ── Sanity: shipping examples never trigger errors ─────────────────────────

frontend/src/simulation/verify/circuitVerifier.ts

@@ -36,6 +36,8 @@ export type WarningCode =
   | 'over-voltage'
   | 'reverse-polarity'
   | 'missing-connection'
+  | 'power-short'
+  | 'shorted-component'
   | 'resistor-overpower'
   | 'led-no-current';
 
@@ -211,6 +213,45 @@ export async function verifyCircuit(
     }
   }
 
+  // Power rail tied to ground: a wire directly joining a VCC-type pin and a
+  // GND-type pin shorts the supply to ground. When a board drives the rail and
+  // no battery/signal-generator source is present, the current-based
+  // short-circuit rule (which only inspects those sources) misses it — so name
+  // it structurally here. Blocking error.
+  const VCC_PIN_RE = /^(vcc|vdd|vcc_rail|5v|3v3|3\.3v)$/i;
+  const GND_PIN_RE = /^(gnd|vss|vee|ground|gnd\.\d+)$/i;
+  let powerShortReported = false;
+  for (const wire of input.wires) {
+    const a = wire.start.pinName;
+    const b = wire.end.pinName;
+    const shorted = (VCC_PIN_RE.test(a) && GND_PIN_RE.test(b)) || (GND_PIN_RE.test(a) && VCC_PIN_RE.test(b));
+    if (shorted && !powerShortReported) {
+      powerShortReported = true;
+      errors.push({
+        severity: 'error',
+        code: 'power-short',
+        message: `Power is shorted to ground — a wire connects a VCC pin (${a}) directly to a ground pin (${b}). Remove that connection; it would dump the full supply current through the wire.`,
+      });
+    }
+  }
+
+  // Two-terminal part shorted across itself: both terminals on the same net, so
+  // it carries no voltage and has no effect on the circuit. Non-blocking hint.
+  for (const comp of input.components) {
+    const pins = twoTerminalPins(comp.metadataId);
+    if (!pins) continue;
+    const n0 = pinNetMap.get(`${comp.id}:${pins[0]}`) ?? (pins[0] === '−' ? pinNetMap.get(`${comp.id}:-`) : undefined);
+    const n1 = pinNetMap.get(`${comp.id}:${pins[1]}`) ?? (pins[1] === '−' ? pinNetMap.get(`${comp.id}:-`) : undefined);
+    if (n0 !== undefined && n1 !== undefined && n0 === n1) {
+      warnings.push({
+        severity: 'warning',
+        code: 'shorted-component',
+        componentId: comp.id,
+        message: `${comp.metadataId} ${comp.id} has both terminals on the same node — it is shorted out and has no effect on the circuit.`,
+      });
+    }
+  }
+
   let solve: ElectricalSolveResult | undefined;
   try {
     const cooked = await runSpice(netlist);