feat(core): event queue, Ethernet, switch, ARP, IPv4, ICMP, routing and firewall

First slice of the TypeScript port of the filius-ipad runtime engine,
with 29 tests ported from the Swift suite. Parts not ported yet throw
NotPortedError instead of guessing.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

packages/core/src/runtime/snapshot.ts

@@ -0,0 +1,90 @@
+// Ported from filius-ipad (GPLv2/GPLv3):
+//   State/TopologyNetworkRuntimeEngine.swift (TopologyNetworkRuntimeTopologySnapshot)
+// What the runtime starts from: the topology and every configuration, frozen
+// at the moment the simulation starts. Later protocol slices add their
+// configuration maps here (DHCP, NAT, remote link, wireless).
+
+import { compareIds, type Id } from '../ids.js';
+import type { NodeKind } from '../model/node.js';
+import { canonicalMacAddress } from '../model/node.js';
+import type {
+  DeviceConfiguration,
+  FirewallConfiguration,
+  InterfaceConfiguration,
+  InterfaceKey,
+  ManualRoute,
+  SwitchConfiguration,
+} from './config.js';
+
+export interface PortSnapshot {
+  readonly id: Id;
+  readonly label: string;
+  /** Canonical, or undefined for a port whose MAC address is derived from its id. */
+  readonly macAddress?: string;
+}
+
+export function portSnapshot(id: Id, label: string, macAddress?: string): PortSnapshot {
+  const canonical = canonicalMacAddress(macAddress);
+  return canonical === undefined ? { id, label } : { id, label, macAddress: canonical };
+}
+
+export interface NodeSnapshot {
+  readonly id: Id;
+  readonly kind: NodeKind;
+  readonly ports: readonly PortSnapshot[];
+}
+
+export interface LinkSnapshot {
+  readonly id: Id;
+  readonly sourceNodeId: Id;
+  readonly sourcePortId: Id;
+  readonly targetNodeId: Id;
+  readonly targetPortId: Id;
+}
+
+export interface TopologySnapshot {
+  /** Sorted by id (Swift `uuidString` order). */
+  readonly nodes: readonly NodeSnapshot[];
+  /** Sorted by id (Swift `uuidString` order). */
+  readonly links: readonly LinkSnapshot[];
+  readonly deviceConfigurations: ReadonlyMap<Id, DeviceConfiguration>;
+  readonly interfaceConfigurations: ReadonlyMap<InterfaceKey, InterfaceConfiguration>;
+  readonly manualRoutesByNodeId: ReadonlyMap<Id, readonly ManualRoute[]>;
+  readonly ripEnabledByNodeId: ReadonlyMap<Id, boolean>;
+  readonly firewallConfigurationsByNodeId: ReadonlyMap<Id, FirewallConfiguration>;
+  readonly switchConfigurationsByNodeId: ReadonlyMap<Id, SwitchConfiguration>;
+}
+
+export interface TopologySnapshotInput {
+  nodes: readonly NodeSnapshot[];
+  links: readonly LinkSnapshot[];
+  deviceConfigurations?: ReadonlyMap<Id, DeviceConfiguration>;
+  interfaceConfigurations?: ReadonlyMap<InterfaceKey, InterfaceConfiguration>;
+  manualRoutesByNodeId?: ReadonlyMap<Id, readonly ManualRoute[]>;
+  ripEnabledByNodeId?: ReadonlyMap<Id, boolean>;
+  firewallConfigurationsByNodeId?: ReadonlyMap<Id, FirewallConfiguration>;
+  switchConfigurationsByNodeId?: ReadonlyMap<Id, SwitchConfiguration>;
+}
+
+export function topologySnapshot(input: TopologySnapshotInput): TopologySnapshot {
+  return {
+    nodes: [...input.nodes].sort((lhs, rhs) => compareIds(lhs.id, rhs.id)),
+    links: [...input.links].sort((lhs, rhs) => compareIds(lhs.id, rhs.id)),
+    deviceConfigurations: input.deviceConfigurations ?? new Map(),
+    interfaceConfigurations: input.interfaceConfigurations ?? new Map(),
+    manualRoutesByNodeId: input.manualRoutesByNodeId ?? new Map(),
+    ripEnabledByNodeId: input.ripEnabledByNodeId ?? new Map(),
+    firewallConfigurationsByNodeId: input.firewallConfigurationsByNodeId ?? new Map(),
+    switchConfigurationsByNodeId: input.switchConfigurationsByNodeId ?? new Map(),
+  };
+}
+
+/** The same snapshot with some fields replaced (Swift rebuilds it field by field). */
+export function withSnapshot(
+  snapshot: TopologySnapshot,
+  changes: Partial<TopologySnapshotInput>,
+): TopologySnapshot {
+  return topologySnapshot({ ...snapshot, ...changes });
+}
+
+export const EMPTY_TOPOLOGY_SNAPSHOT: TopologySnapshot = topologySnapshot({ nodes: [], links: [] });